Part 17 - - Offline - Dibble Sticks Donkeys and Diesels

Part 17 - - Offline - Dibble Sticks Donkeys and Diesels
A project of Volunteers in Asia
By: Joseph K. Campbell
Published by: The lnternational Rice Research Institute
P.O. Box 933
Manila, Philippines
Available from: The International Rice Research Institute
P.O. Box 933
Manila, Philippinos
Reproduced with permission.
Reproduction of this microfiche document in any form is subject to the same
restrictions as those of the original document.
,. .
Department of Agricul&l
Biological Engineering
Cornell University
Ithaca, New York, USA
International Rice Research Institute
PO. Box 933, Manila, Philippines
The International Rice Research Institute (IRRIj was es?ablished in 1960 by the Ford
and Rockefeller Foundations with the help and approval of the Government of the
Philippines. Today IRRI is one of the 13 nonprofit international research and training
centers supported by the Consuhative Group on International Agricultural Research
(CGIAR). The CGIAR is sponsored by the Food and Agriculture Organization
(FAO) of the United Nations, the International Bank for Reconstruction and
Development (World Bank), and the United Nations Development Programme
(UNDPI. The CGIAR consists of 50 donor countries, intematioaal and regional
organizations. and private foundations.’
IRRI receives support, through the CGIAR, from a number of donors including
the Asian Development Bank, the European Economic Commimity. the Ford
Foundation, the International Development Research Centre, the International Fund
for Agricultural Development, the OPEC Special Fund, the Rockefeller Foundation,
the United Nations Development Programme, the Worid Bank, and the international
aid agencies of the following governments: Australia, Belgium, Brazil, Canada,
China, Denmark. Finland. France, Federal Republic of Germany, India, Iran, Italy,
Japan. Republic of Korea, Mexico. The Netherlands, New Inalond. Norway, the
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The responsibility for this publication rests with the International Rice Research
[email protected] International Rice Research Institute 1990
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ISBN 971-104-185-5
To Signd, Sabine, i)liuer, ma’ Midori, thank you
Tbads also to Eric &lcCcw.
Why mechanization? 1
Units and their use 3
Human and Animal
Engine power 41
Tractor horsepower 44
Single-axle pedestrian tractor 45
Double-axle pedestrian tractor $50
Compact tractor 51
Farm tractor 53
Single-wheel pedestrian tractor 66
Motorcycle tractor 67
Winch systems 68
Rotary power from animals
Relationships among energy, work, and power
Human power 7
Animal power 9
1.3.1 builocks 14
1.3.2 Water buffalo 21
1.3.3 Elephants 23
1.3.4 Horses 23
1.3.5 Mules 32
1.3.6 Donkeys 33
1.3.7 Camels 33
Climate, soil, and farming Fystems 73
Shifting cultivation 74
Polyculture 77
Monoculture 79
Cropping calendars 81
Soil tilth and compaction 81
4.1 Tillage tool classification 89
4.2 Hoes 90
4.3 Spades and shovels 91
4.4 Foot plows 93
4.5 Ards 94
4.6 Chisel plows 96
4.7 Field cultivators 99
4.8 Subsoilers 99
4.9 Moldboard plows 101
4.13 Disk plows 110
4.11 Laying out a field for plowing
4.12 Rotary tillage tools 111
4.13 Harrows 115
4.14 Puddlers 124
large seeds 129
small seeds 136
cuttings and tubers
seedlings 147
Rate of manure production by animais 154
Hand tools for applying manure 154
Machines for spreading manure 155
6.3.1 Box spreaders 155
63.2 Flail spreaders 158
6.3.3 Closed-tank spreaders X58
Machines for applying chemical fertilizer 159
6.4.1 Dry fertilizer 160
6.4.2 Liquid fertilizer 163
Weed Control
for planting
for planting
for planting
for planting
Mechanical weed control 167
7.1 .I Manual tools 16s
7.1.2 Animal- and tractor-pox+:ered machines
Chemical weed control 174
Insect and Predator Control
8.1 Mechanical control 183
Chemical control
[email protected]
9.1 Grain harvesting 189
9.1.1 Hand tools 190
9.1.2 Reapers 196
9.1.3 Threshers 199
9.1.4 Combines 205
9.2 Root and tuber harvesting 211
9.3 Forage harvesrtny 217
9.3.1 Hand tools 217
9.3.2 Mowing machines 218
9.3.3 Conditioners and rakes 221
9.3.4 Forage harvesters 227
9.3.5 Hay balers 231
9.4 Fiber harvesting a,nd field processing
9.4.1 Cotton 235
94.2 jute 238
Kenaf 239
9.4.4 Fiax 239
9.45 Coir 241
9.4.6 Sisal 241
9.4.7 Abaca 243
Grain Drying
and Storage
Basic principles 247
Cribs 251
Dryirig with heat 253
Drying with forced air 257
Resistance of grain to airflow 258
Fan characteristics 260
Combined forced-air and heat drying systems 261
11.1 Manual transport 273
11.1. I Carrying pole 274
11.1.2 Bicycles 277
11.1.3 Wheelbarrows and handcarts
11.2 Animal transport 281
11.3 Tractors 285
Social Consequences
Mechanization and agricultural employment
Mechanization and crop yield 293
Mechanization and farm income 295
Affordable technology 295
Mechanization and quality of life 297
13.1 Estimating the cost of field machinery 301
13.2 Multipurpose machines 313
13.3 Examples of estimating the cost of field w-Lm*eP
Metric-English conversions 319
Rates of work, draft, and power 321
Bullock training 326
Nebraska ‘Tractor Test 328
I.>ihhk Sticky Dodxy,
ad ,Lksel.s:Macbi~ws i tx c’,7rlI~Pm-
drrc:tiorl is :I lmxid study of qgricultural nxxhanization. from
simple hand tools to self-propelled harvesters. l‘he Ixmk is
for the non-a~riciiltural engineer who wmts to learn at~joutthe
wide diversity of power and machines cased by kumers
produce our staple food :!nd fiber crops, It proviclcs the reader
with ird&Illatir)il needed to bYigh the :Iclv~lnt:rgesand clisadvantages of specific types of nl;~chine~. For es:lnl~:le. what are
the trade-offs IWtvcen ;i pedestrian tT;Ictor and ;I hyc!roti!ltrr?
short-handled hoes used
in .M’ric:l? For human
cmying stick of
transport of Ioads, why is the litnbcr l~m~nhoo
Asia suptxior to the rigid poles used in some other ccxmtries?
The author.Josepll li. Cxiiplwll.
xnswers these :ind nun)
other questions in this survey of technological cle\:c!cqx~lent
in crop production. O\vr the last 100 yexs. the shilt from
muscle to engine power h;u clxing~d
agric7.ilture cirmiatic~all~.
Often ignored. however, is thz ~-LcTthat most of the fxm~rs
in the world still clcpcncl on x%ni:il power 2s their nuin sourc‘e
of draft energy.
The lessons learneci in recent ciecxles are importmt to
document. We now know that direct transfer of knowleclg~
from one environment to mother often leads to mmng
solutions to critical prot%ms. At the same time. it is most
to li~iow
where. and whv teclinologic:d
took place.
With this information, the adaption of
knowledge and the cle\~~lopnler~t of technological solut:iims
accorcling to loc:il needs are easier I:0 achieve.
Not many people toti:iy li;i\~
conit~ineci skills to
compile the kind ofinform;~tion lhincl
in this lmok. Prof~:ssor
c:[email protected] has more than .tO years d wtxlclwicic expericncc in
He wis
born into ;I Fumily of Penns$vania
~farmers and learr-4 about crop production literally from the
ground up. He chose agricultural engineering as his profession, earning his bachelor’s degree at Pennsylvania State University and his ii:aster’s at Cornell University. Since 1967 he
ins been on the faculty of Cornell, where he is Professor of
Agricuitural Engineering. He worked as an in-house consultant at the Int&national Potato Center in Peru and spent two
years at the International Rice Research Institute in thr [email protected] Short-term consultancies have taken him t.o Bangladesh, Ecuador, Egypt, Ghana, Kenya, Nigeria, Pakistan,
Paraguay, and Zaire. Professor Campbell has also had extensive practical experience as a design engineer for a leading
manufacturer of agricultural implements.
Dibble Stictq Don&vs, and Diesels will be a valuable
resource for development workers, economists, extension
officers, administrators, students! and agriculturalists throughout the developed and developing world.
Klaus Lampe
Director General
Why mechanization:
In industrinl countries, mechanization lowers crop production
costs by replacing labor with machines. It is therefore
reaonable to question the desirability of mechanization in
less developed countries (LDCs), which ~~sualiy have barge,
unl:ipped sources of labor and small farms.
Crops are producec! by the iilteraction of sunlight, water,
and nutrients. Man can utilize energy to improve conditions
for crop growth. For example. the manipulation of plant
spacing can affect the efficiency of sob energy in producing
food through photosynthesis. However, 3 small plot utilizing
mechanization may produce no more than the same plot
farmed solely by sufficient human energy.
Increased food production is often linked to mechanization. linlike ;L factory. :I farm is at the mercy of natural
phenomena such as water, temperature, and daylength. over
which the farmer has little control. The f’armer’s ability to
cultivate within the time provided by the rhythms ant! whims
of nature determines the xlecp~y
of crop yield. Approximately the s;m~e amount of work is required to prepare the
soil for planting, whether accomplished by ;I man fueled by
rice, 3 w23ter buffalo fueled by forage, or a tractor fueled by
petroleum. In many countries, tillage must be carried out
during the rainy season hecause txither farmers with hoes nor
animal-drxvn plo~vs have sufficient power to tiil hard, dry
soil. Mechanization in the form of an animal&awn steel plow
or ;i tractor, however, can prepare the soil tiefore the rains to
permit either a longer growing period or more than one
annual crop.
The relationship between social structure and mechanization is not always obvious. Substituting a 100-horsepower
(hp! tractor with a seven-bottom plow for a 50-11~tractor with
a three-bottom plow makes sense to a New York dairy farmer
on a family farm where the work force consists of the father,
two or three children, and a hired man. Dairy cattle require
care throughout the year, but at peak periods there is
increased demand for labor for fieldwork, plowing, planting,
and harvesting. The large machines allow this farmer to plow
seven furrows simultaneously instead of three, and to harvest
maize for forage at a rat.e of 40 tons per hour (t/h) instead of
15 t/h. This farmer’s use of power and mechanization is economically advantageous, since planting can be accomplished
during the few days the soil is suitable in the spring, and
harvesting can be completed before fall rains cause crop
losses. Of course, a farmer’s capital or a nation’s resources can
be wasted through inappropriate mechanization.
Mechanization of small holdings in LDCs with high rates
of unemployment OTunderemployment is a difficult problem.
Often the extended family is the primary social system. A
person is responsible not only for his parents and siblings, but
for aunts, uncles, and cousins. Since there is little opportunity
to earn a wage away from the family farm in this type of social
system, labor is often augmented by ciistant relatives. The
farmer must provide them food and shelter whether or not
they work. What matters to the workers is not iack of
employment, but lack of food.
What determines their
standard of living is not underemployment, but the total farm
production. In such cases, mechanization benefits all concerned if it increases total farm prodilction.
In addition to improved plant varieties, water management, fertilizers, credit, and government food pricing policies,
appropriate mechanization plays an essential part in increasing food production and the standard of living in rural areas.
Climatic conditions in the developed countries of the
temperate zone generally permit only one grain crop per year.
In the north temperate zone, much of the land is dormant from
the first frost in October to the last frost in May. These
conditions are not worldwide.
One should not consider
agricultural problems with a bias in favor of the agricultural
practices of one area. Although one grain crop per year is the
norm in the temperate zone, in the sunny, frost-free tropics,
food crops can be grown throughout the year.
Where more than one crop per year is cultivated, it is
important to reduce the time between hariest of one crop and
planting of the next. For example, a 125-d rice variety,
yielding 3,000 kg/ha per crop, has a cost of 24 kg/ha for each
day the land is idle. Therefore the use of machinery to speed
land preparation and plantin of the next crop provides an
additional 24 kg rice/ha for Cdl day saved in establishing the
next crop.
IJnits and their use
Metric or English? In general, North American farmers use the
English system of measurement, and European farmers use
the metric system. Mixtures of the two systems and local units
of measurement are used throughout the world. For example,
Peru is officially metric, but its citizens use hectares, meters:
and kilograms (r.etricj as well as board feet, horsepower. and
national fine and national course screw threads (English).
Adding to the confusion is the existence of more than one
metric system. For many years, the word kilogram has been
used as the unit for borh lwass and force. This caused few
practical problems for agriculturists, since they work on the
earth’s surface where gravity is 11g, and kilogram mass (kg)
and kilogram force Ckgf) are numerically the same. In 1960,
however, the 11th General Conference of Weights and
Measures adopted an expanded metric system called “Le
Syst,eme Internatiotial d’Unites” (3). SI expresses mass in
kilograms, but force is expressed in newtons.
In the interest of universal comprehension, when non-S1
systems of measurement are used in this book (either for
understanciing or because the original research w:ls conducted in such units), the Si equivalent is given in parentheses. For example, a test of a compact tractor revealed that
under specific conditions the tractor provided a pulling foric
of 948 pounds. This will be expressed as 948 lb (4,217 N,
430 kgf).
These primary units of measurement are used in this
Metric St
Metric kg force
degree Celsius
kilogram of mass
kilogram of force
degree Celsius
foot-pound or calorie
British thermal unit
degree Fahrenheit
pounds/square inch
Time is expressed in minutes (min13 hours (I$, days (d),
weeks (wk>, month (mo), and years (yr).
English-to-metric conversion factors are listed in Appendix A.
IH uman
animal po
Land cannot be tilled, seed cannot be planted, and crops
cannot be harvested without energy. The various forms of
human and animal power and the means of harnessing them
for agriculturel as well as their characteristics, advantages, and
limitations, are discussed ir! this chapter.
1.1 Relationships
among energy, work,
and power
This book ‘uses the words force, work? power, and energy in
the engineering sense.
A.fbrce can be visualized as a pull or push that tends to
move an object. For example, a force of 2500 N (255 kgf, 562
lb) is required to move a plow through the soil. In tillage tools,
this force is usually referred to as drajt. Whether the plow is
pulled a meter or a rnilel the required draft in this example is
2500 N.
The term UJCX%includes the dimensions of force and
distance. Work equals force multiplied by distance. The
metric SI unit of work is the joule (I), and the metric kiiogrdm
force unit is kilogram-meter (kg-m). The English unit is the
foot-pound (ft-lb). The time required to do a job is not part
of the definition of work. To plow one hectare of land
requires the Same amount of work whether the job is
completed in a day or an hour. However, the power
requirements are very different.
Pou:cr is the rate at which work is performed. The faster
the work is done, the greater the power requirement. In the
English system. horsepower is the power unit. One horseHorsepower is the rate at
power equals 33,000 ft-lb/min.
which a large draft horse can perform work. When the l&h,
century Scotsman, James Watt, was designing steam engines,
he was faced with prospective customers insisting on know-
ing the precise number of horses that could be replaced by
one of his engines. Accordingly, Watt experimented with
draft horses and determined the power generated by a horse
exerting a constant 150-lb pull while walking 2 l/2 miles per
hour (mph). Watt called this amount of power “one horsepower.”
The common units of power in the metric system are the
kilowatt (kW) and the metric horsepower. Metric horsepower
is also knoy>.-qas pferde star& (ps). One metric horsepower
(ps) equals 4500 kg (force)-m/min.
1 kW
1 hp
1 Ps
1 hp
1 hp
1 Ps
1,000 N-mlsec
550 ft-lb/set
7.5 kgf-mlsec
745.7 N-m/set
1.014 ps = 0.746 kW
0.966 hp = 0.735 kW
For example, if the plow in our example is pulled with
a force of 2500 N (255 kgf, 562 lb) for a distance of 500 m
(1640 ft) in 10 min, the power expended at the plow would
kw = 2500 Nx500m
600 set
hp =
255 kg x 500 m
600 set
5621bx 1640R
600 set
+ 1000 N-m/set per kW = 2.08 kW
+ 75 kg(force)-m/set
per ps = 2.83 ps
+ 550 ft-lb/set per hp = 2.79 hp
Metric horsepower and English horsepower are nearly
equal. This book will therefore use the term honepower
rather than kilowatt, since it is easier to visualize a large draft
horse than 0.746 kW.
Energy, heat, and work are expressed in joules in the SI
system. However, it is common to express energy and heat
ir, special units - the calorie (c> in the metric kilogram force
system and the British thermal unit (BTU) in the English
system. The BTU is the quantity of heat required to raise the
temperature of 1 lb of water 1 “F. The kilocaiorie is the
quantity of heat required to raise 1 kg of water 1 “C. The
calorie (l/1000 kilocalorie> is used in some disciplines and is
represented by a lowercase “c.” The kilocalorie is represented
by a capital “C.”
1.2 Human power
Man develops a total power of 0.5 hp from the food he eats.
However, only, 0.1 hp is available for usefill work. The
remainder is expended on bodily functions-, (~basal metabolism). This norm is based on an adequately fed 35-year-old
male European laborer working an 8-h day and a 48-h week.
A mar; of 20 can generate approximately 15% more useful
energy than the norm, and a 60-year-old about 20% less.
&sed on the above norm, an equ”tion for use&i1 power
for work lasting from 4 min to 8 h can be expressed by the
equation: hp = 0.35 - 0.092 Iog 1 where t is in minutes.
Work period
4 min
15 min 30 min 1 h
Power (hp)
0.16 0.13 0.11
The equation predicts that a man can prov~ide work at the
rate of nearly 0.3 hp for 5 min, but at only 0.1 hp over 8 h. A
muscles also provide an overload en.ergy capability of
appro.ximately 0.6 hp-min. For bursts of energy for less than
one second, up to 6 hp may be expended.
Pedaling makes use of thr large leg muscles (Fig. I.1 ). For
periods of time from 1 to 100 minutes, a man pedaling can
generate useful power of 0.27-0.53 hp. This is expressed by
the equation: hp = 0.53 - 0:l.Y log t where t is in minutes.’
Work period
1 min 10 min 15 min 30 min 45 min 1 h
Power (hp)
1.5 h 1.7 h
0.30 0.28 0.27
A person can exert approximately 55 kgf (120 lb. 540 N)
by pushing or pulling. Using carrying support.~, :I person can
carry a load equal to his own weight for short distances of
about 50 m (165 ft). For long distances, the load should not
exceed half a person’s weight.
Humans require energy in the form of food. Food energy
of 2000 C per day is minimal input. Conversion efficiency is
the ratio of useful energy from the person to the food energy
consumed. The higheb: conversion efficiency is 25%. Human
work efticiency decreases under hot and humid conditions,
for humans as well as machines conform to the laws of
Human efficiency decreases when the
1.1. Human-powered treadle
pump in Bangladesh.
ability to dissipate heat through evaporation. convection, or
radiation is diniinished by tropical climate. Humans cannot
compete successfully with animals or engines as a source of
power for repetitive jobs such as pumping water for irrigation.
A human is at a disadvantage because of low power output.
A person is unique, however, because of intelligence. For
jobs having low pot.-er requirements but demanding decisionmaking and manual dexterity, humans are well adapted.
For example, transplanting vegetables or rice demands dexterity of hand as well as thought. Does the transplant have
sufficient roots? Is the spacing correct? A person transplants
better than machines or animals.
Although the reader will probably not be called upon tcr
act as an energy source in agriculture! an attempt to under-
stand the position of the Third World farmer, whose own
energy is the power source for the farm, would be informative . The farmer is probably underfed, suffering from
parasites, working under the hot sun, and aware that the work
will be hard not only today, hut also tomorrow, the day afteii,
and the day after that. A water pump designed for poor
farmers in LIXs may be a lark to operate at an exhibition in
Washington, D.C., where the visitor operates it for only
several minutes, but it will not be viewed so idealistically by
farmers in the LLXs.
1.3 Animal
The large domesticated four-footed animals commonly called
draft animals are an essential source of power in agriculture.
Dr:lft animals provide approximately 80% of the world’s
agricultural draft requirements. Table 1.1 lists the world’s draft
animal and tractor population by regiorl.
Drclfi is a suitable term for animals used in agriculture, for
the animai’s strength is nearly always convert.ed to useful
work by the animal pulling against a load, whether it be an
ox pulling against a head yoke or a horse against its collar or
breaststrap. Oxen, water buffalo, horses, and mules are the
primary draft animals. Camels and donkeys are more typically
used as pack animals, although they are used for pulling carts
and plows in some countries.
An animai can do four things that a tractor cannot do: feed
itself, maintain itself, be trained for automatic control, and
Table 1.1. Total number of tractors and selected animals in the world.2
Central America
South America
'USA population is included in North and Central America.
bUSSR population is not included in Asia or Europe.
reproduce itself~ Viewing the draft animal as a machine, we
see a jointed framework held together with ligaments and
muscles. The engine consists of the digestive organs, while
the excretory system carries away waste products. The brain
and nervous system provide a control system with a memory
bank and logic circuits. Joints and moving parts have a sealed
lubricating system. ~Protecting the mechanism is a skin and
hair covering resistant to damage, and self-healing if the
damage is minor.
The energy efficiency of animals is the subject of considerable disagreement. The Food and Agljculture Organization
(FAO) states that the energy efficiency is 9-10% for bovines
and lo-12% for the horse family.3 P.S. Rose, on the other hand,
states that the horse has an efficiency of about 20% and man
19.6%.4 The difference between these authorities is probably
due to the means by which work is obtained from the animal,
whether by draft or by a treadmill. The efficiency of energy
conversion is 20-35% for gasoline and diesel engines.
Generally, a draft animal’s force is approximately 10% of
its weight. I-lorses have a higher output than other animals.
Unlike a tractor, an animal cannot be worked continuously.
The period during which an animal can be worked daily
usually varies from 8 to 10 h for horses and mules, and from
6 to 8 h for adult oxen. Table 1.2 lists the normal draft and
power of various draft animals. It is impossible to provide
precise data for draft animals, since performance depends on
individual characteristics such as breed, weight, sex, age,
health, training, and quality of feed.
Just as an internal combustion engine requires high
quality petroleum fuel to perform well, an animal requires a
sufficient amount of high quality fuel in the form of feed in
order to develop maximum power. The availability of feed
affects the choice of draft animal. For example, the horse is
usually preferred to the ox because of the former’s greater
speed, maneuverability, and power output. Oxen can work
satisfactorily on low quality forage, however. A horse must
have grain to perform well. Slither van Bdth, in 7beAgrartan
History of Western Europe, states that in Europe, when tools
and social conditions made possible a shift from a two-course
rotation (land left fallow in alternate years) to a three-course
rotation (where land lay fallow one year out of three), a larger
oat harvest could be produced, making it possible to feed a
Table 1.2. [)Lrafland horsepower of various animals.5
in kgf (ib)
500 - 900
60-80 (130-l 75)
Water buffalo
400 - 600
400 - 900
50-60 (110-130)
50-80 (110-175)
Light horse
400 - 700
60-60 (130-i 75)
350 - 500
50-60 (110-I 30)
200 - 300
450 - 500
30-40 ( 65 90)
40-50 ( 90-l IO)
80 - 90
30 ( 65)
greater number of horses.’ He further notes that during times
of increasing agricultural prosperity a shift occurs from oxen
to horses. He lists several explanations for this:
l The pace of an ox is slower than that of a horse, so an
ox does much less work. But the ox is cheaper to feed.
The ox saves food, while the horse saves man-hours.
Sixteenth century French writers stated that one horse
could do as much work ir, a day as three or four oxen.
Especial!y in a damp climate, the speed at which certain
tasks can be accomplished is of vital concern.
Newly reclaimed land is often poorer and lig:~tcr and
therefore easier to work.
The higher cash profit for cereals during a period of
reclamation allows farmers to spend more on haulagepower.
l During a boom, social prestige pkiys a greater part.
farmer with horses stands higher in the social scale than
one who keeps only oxen.*
Neither high draft nor high speed by itself indicates high
power output. Power is the product of draft and speed.
= draft (lb) x speed (mph)
375 lb-mph
draft (kgf) x speed (km/h)
270 kg-km/h
For example, a particular ox may pull a load with a force
of 80 kgf (176 lb, 785 N), while a horse may pull with a force
of only 60 kgf (132 lb, 588 N); but the horse with that particular
load moves at 3.5 kmih, while the ox moves at 2 km/h. IJnder
these conditions the horse provides 0.8 hp and the ox 0.6 hp. can, over a short period of time, develop much
higher power than that produced during normal work. For
example, a good pair of draft horses can develop 20-25 hp for
10 sec. while a yoke of good oxlzn can generate 20-30 hp over
a distance of 100 m. Excessive overloading, however, will
harm the animals.
The energy of the animal is converted to useful WOI-K by
the harness. A poorly designed and ill-fitting harness not only
reduces the power available from the animal, but causes the
animal to suffer by chafing or interfering .with breathing.
When draft greater than can be provided by one animal
is required, two or more animals are harnessed t.ogether to
pull as a team. An efficiency loss for the individual animal
res:rlrs when harnessed in a team. When harnessing animals
of equal strength together, the draft of the individual should
be multiplied by 1.9 for two animals, 2.5 for three, 3.1 for four,
3.5 for five, and 3.8 for six. For example, if one ox can provide
a draft of 600 N (61 kgf, 135 I$I: then a yoke of 2 oxen can
provide 1.9 x 600 N or 1140 N. If 6 oxen are yoked together,
the draft is 2280 N-only dou’:,le that of 2 oxen. Ar:imals of
the same breed, age, fitness, ;md training should be used in
a ream. Otherwise, the weak or ill-trained individual will
reduce the team’s output.
Figure 1.2 shows an evtaner used to hitch three draft
animals to one implement. ‘I‘:?e points where the sing!etrees
pivot on the cvener provide :~:everJlclosely spaced holes for
the pins securing the single trees. These holes allow for
adjustments in the length of the lever arm against which an
anim;ll is pulling. Allowances can thus be made for weaker
or stronger members of the team so the evener is not pulled
It is easier to pull a bdci on the level than up a slope, since
on a slope the !oad must be lifted as well as pulled forward.
The draft of an animal is therefore reduced when pulling a
load up a slope. The angle of the slope is usually referred to
as percent grade, which is defined as units of vertical rise per
100 units of horizontal distance. For example. a rise of 1 m
1.2. Evener for a team.
per 100 m horizontal distance is a 1% grade. The draft of a
horse is reduced by 10% on a 1% grade, 20% on a 2% grade,
35% on a 3.3% grade, 60% on a 5% grade, and 75% on a 10%
grade.” Draft requirements for scme fanning operations are
given in Appendix B.
Brody has examined data on men and horses working at
various levels of effort. His work enables one to estimate the
power output of draft animals of various sizes and conditions.
If the power a draft animal can produce during heavy work
over a 6- to 10-h day is considered 1, the maximum power
maintained for 5-320 mimtes is 4 times as great, and the
maximum power that con be exerted over a few seconds is 25
times as great.”
In general, power produced by draft animals such as
bullocks, horses, water buffalo, and elephants can be estimated by their mass in relation to man.
hpA = hp, x
A = animal
Using the previously
M = man
stated estimate for man’s power
hp, = (0.35 - 0.092 log t) x
Tractors develop less ti lan their designed capacity because of mechanical maladjustments or failures. Draft animals
are subject to biological problems and breakdowns. Horses
and cattle cannot be used in one-fourth of Africa, for example,
because of the disease trypanosomiasis, which is spread by
the tsetse Ry, a bloodsucking insect of the genus Glossina.‘l
The tsetse and its accompanying trypanosomiasis parasites
affect Equatorial Africa south of the Sahara in a band from
about 15” N to 20’S latitude. Trypanosomiasis (popularly
known as sleeping sickness) debilitates and kills thousands of
humans and animals each year. In animals, the parasites are
Trypanosoma brucei, Typanosoma congolense, and Typanosoma vivax. In humans, the parasites are Trypnnosoma
gambiense and Typanosoma rhodesiense. Although zebu
cattle are susceptible to trypanosomiasis, some breeds such as
N’dama and Muturu have some tolerance for the disease.
Foot and mouth disease kills both cattle and water buffalo.
In 1975, an outbreak in the Philippines, accompanied by
government guaranteed loans for agricultural machinery,
resulted in very rapid spread of pedestrian tractors to replace
the affected animals.”
1.3.1 Bullock The terms ox, bullock, and steer are used to
describe a castrated bovine (Fig. 1.3). The terms ox and
bullock apply to animals trained for draft purposes. Uncastrated bulls are strong, but frequently unmanageable. Cows
lack strength. The bullock, therefore, with its strength and
manageability, is preferred.
It is important that bullocks
selected for purchase have good temperament. Sound feet
and legs with free action are also necessary attributes. The
1.3. Nomenclature of an ox.
feet should be large with solid, hollow-soled hooves.
An ox to be used with a head yoke requires a short,
powerful neck and thick nape. Its horns should be medium
length, angled forward, and set in a wide head. If the animal
is to be used with a shoulder yoke, its shoulders should be
solid rather than sloping, and it should have a hump to help
keep the yoke in place.
Bullocks should be trained for draft work when 2-3 yr old.
A typical training program is shown in Appendix C. If well
managed, a draft bullock should perform satisfactorily for
about 17 yi
Cukivation trials using N’dama bullocks in Gambia revealed tha’r work in excess of 5 h/d can be sustained only over
a few days. After 3 h of heavy morning work, each bullock
lost an average of 25 kg. With adequate pasturing, the
bullocks normally recovered, but at times the losses were
cumulative and affected the bullocks’ health. A double head
yoke was used in the trhls. The work and power output of
a bullock depend on body weight, hours of continuous work,
and climate.*j
At the International Crops Research Institute for the SemiArid Tropics (ICRISAT) in Hyderabad, India, tests”’ revealed
that trained and adequately fed Indian bullocks (Bos indictls)
of the Hallikar breed, 8-14 yr old, could pull maximum draft
loads of 13-16%of their body weight for a 6-h period. During
a 6-h working day, the average speed, power, and work
output were 3 km/h, 0.9 hp, and 14.0 megajoules (5.2 hp-h1
of work per pair.
The speed, power, and work output increased with body
weight. Although power and work output increased with
additional draft load, there was a proportionate rate of
decrease in speed. At maximum draft load, moreover, the
bullocks could not wofk as many hours per day. Speed and
power decreased as the hours of continuous work increased.
At the end of 6 h of continuous work, speed and power were
reduced by 75%.
The vertical force of a yoke on a pair of draft bullocks
should be kept below 60 kgf (575 N, 132 lb) to prevent
excessive stress.
The Indian bullocks also performed better in a cool, dry
climate (26 “C, 35% relative humidity [RH]) than in a warm,
humid climate (29 “C1 57% RH).
Bullocks for draft purposes are usually harnessed in pairs
or multiple pairs.
The harness is the means by which the animal is connected to the tool so that work may be accomplished. In some
regions, the harness is used principally as a me:lns of animal
control, and energy transmission is secondary. In other
regions, the harness is principally for energy transmission,
while control. of the bullock is accomplished by good training,
well-fitted yokes, traces, and verbal commands.
In gene:al, pairs of oxen are yoked side by side by either
of two devices: the double head yoke (Fig. 1.4) or the double
shoulder yoke (Fig. 1.5).
There is some disagreement as to the nomenclature of
these two types of yokes. Some call a head yoke a neck yoke
while others refer to shoulder yokes as neck yokes or withers
yokes. The terms head yoke and shoulder yoke are usecl here.
since they are the most descriptive.
The double head yoke is suitable only for strong, shortnecked bullocks. The yoke is fixed at the front or back of the
head and held rigidly by thongs that bind the yoke to the
bullocks’ horns.
The double head yoke fixed to the back of the head is used
iu Spain and Latin America. Because it is tied to the horns, the
yoke must be shaped anti fitted to the individual bullocks.
Since the yoke is not fastened to the animals’ necks, there is
no problem with chafing caused by ill-fitting neck yokes. The
double head yoke, when securely fastened to the horns,
provides the means by which the bullocks can pull, push, 01
brake the vehicle or tool being drawn. Should the implement
1.4. Double head yoke.
1.5. Double shoulder yoke.
strike an obstaclel however, the bullock can be injured unless
there is a device between the yoke and the implement, to
absorb shock.
The double head yoke w’ds not designed for the comfort
of oxen. They are unable to shake their heads when flies
annoy them. In fact, they cannot move their heads at all
except in unison.
The double shoulder yoke is common in Africa, the Near
East, India, and the Mediterranean. It was also the type used
by North American pioneers. In some countries of the Near
East, the double shoulder yoke is also used for donkeys.
horses, and mules. Pads and collars are required when the
yoke is fitted to these animals.
The double shoulder yoke used in North America is a
wooden beam 1.2-2 m long and shaped to fit the top of the
oxen’s necks in the shoulder region. In Africa, the yoke
consists of a pole with fleece shoulder padding. The yoke is
prevented from moving transversely by chains, rope, steel or
wooden U-pins, or by vertical pins on each side of the neck.
The lag pole (tongue) of the implement is attached to a steel
ring or notch in the center of the yoke. If the yoke slips
rearward, the fasteners tend to choke the animal.
Unlike the double head yoke, the dotible shoulder yoke
permits the bullock freedom of movement. In addition, it
allows the line of draft to be applied lower to the ground and
more in line with the backbone of the builock.
advantages are that it does not require a pair of bullocks of
identical size; it can be fitted to hornless bullocks; and it is
simpie to shape and easy to fabricate.
The double shoulder yoke has disadvantages as well,
however. The primary disadvantage is that it can compress
the windpipe and blood vessels in the bullock’s chest. Sores
are apt to be more frequent, especially around the shoulder
blades. Also, the yoke has a tendency to slip rearward
because of the line of draft. Many people consider this yoke
more difficult for driving bullocks, but I believe driving
control results from training rather than the type of yoke.
Implements or vehicles are hitched by long poles or ropes
to the center of the double yoke. The team is usually directed
by the farmer using a long pole or whip in combination with
verbal commands. In some regions a nose rope used as a jerk
line is used to indicate commands. In societies where work
animals are not well trained or are provided with insufficient
food and care, it is sometimes necessary for one person to lead
the team while another operates the plow or implement.
Bullocks are usually harnessed in pairs for heavy work;
but for lighter work, a single animal is often sufficient. A single
head yoke, a simple shoulder yoke, or a collar can be used to
harness a single bullock. Instead of connecting the implement
or vehicle to the bullock with a single heavy pole, pairs of
wooden shafts, ropes, or leather traces with a singletree are
The single shoulder yoke (Fig. 1.6) is used in Southeast
Asia, China, and some European countries. The singletree
(also called swinglrtree, whiffletree, or whippletree~) is essential when hitching a single animal to an implement. Traces
1.6. Singie shoulder iyoke.
connect the singletree to the shoulder yoke. The singletree
provides rotational movement between the implement and
the draft animal. Single head yokes are used in some areas
of Europe. The traces connect the singletree to the outboard
ends of the head yoke.
A collar harness is occasionally seen on a bullock, but
since collars are more expensive than traditional yokes and
have little advantage other than comfort, they are rarely used
in LDCs.
An improvement is the padded shoulder harness (Fig.
1.71,which provides the advantage of a collar harness at lower
cost. The traces are pulled tight only while the animal is
pulling. Unless the traces are used in combination with a wide
single yoke, it is necessary to use a surcingle to support the
traces when not under tension; otherwise they will hang
down and trip the animal. The surcingle is usually a length
of leather or webbing about 8 cm wide with a ring or loop on
each end. It fits over the bullock’s back, and a trace passes
through each ring. The surcingle should be adjusted so that,
when the traces are tight, a straight line exists between the
1.7. Improved shoulder
harness for an ox.
point where the traces pass through the surcingle ring and the
trace attachment points on the yoke and the singletree.
Individual bullocks may be harnessed to pull a single load
with single yokes connected by joining the singletrees. The
center fastening ring of each singletree is fastened to the
opposite ends of a wooden piece called a doubletree. If more
than two oxen are to be hitched parallel, the singletrees are
attached to an evener.
Double yokes of oxen are often hitched together. For
example, six oxen may be hitched to a load by placing three
pairs of oxen in tandem.
Oxen exert draft by friction between their hooves and the
ground. If oxen are to be used extensively on hard pavement,
they should be fitted with shoes. Since bovines have cloven
hooves, they cannot be shod with a one-piece shoe like
horses. To shoe oxen, two half-plates must be fitted to each
A balanced diet and sufficient calorie consumption are as
important for draft animals as they are for people. It is
surprising, however, that many farmers believe that bullocks
can sustain themselves solely on forage. On the contrary,
draft animals must be fed grain to supplement their forage.
The ration a bullock receives depends on its age, its feed,
and the work. The following five daily rations are typical for
feeding draft bullocks in India.
For a 375-kg bullock working an 8-h day:
4.5 kg rice straw
9.0 kg green sorghum
1.0 kg mustard (Brassicajuncea) or 7.0 kg sorghum
0.5 kg rape (Brasica napus)
For the same bullock as above:
if the bullock grazes at least 7 h/d and rests in the shade
when not working, it consumes approximately 25 kg
mixed pasture grass, which supplies sufficient energy
and protein.
For a 450-kg bullock plowing 6 h/d in the hot season:
2.5 kg wheat bhusa (wheat straw chopped into l-cm
11 kg jowar (Andropogon sorghum vulgare) and quara
CQamopsis psomloide$
2 kg gram (Phaseolz&
Normal working ration:
4 kg of fodder/O.45 kg body weight
0.5 kg grain/h of work with a daily maximum of 4 kg
0 Nonworking day’s ration:
4 kg of fodder/O.45 kg body weightI
Most lndian bullocks are fed less than recommended.
Typically, they are fed 15 kg fodder and 1 kg grain daily.
A bullock should have access to about 30 liters (8 U.S. gal)
of water per day. It should be watered twice during each work
pej-iod. Twice daily is sufficient during the idle season. The
fee,iing and care of a bullock are related to its work output.
Large, well-fed bullocks of the Hariana breed provided 8.6 hph of work over a 9-h day, while smaller, poorly fed bullocks
provided only one-fourth that amount.‘”
13.2 Water buffalo. The water buffalo (Bubalus bubalis) is
usually associated with rice production in Asia, but is also
used in Egypt, the Soviet Union, Bulgaria, and Italy. Approximately 200,000 exist in Brazil, where they are raised as a
source of meat rather than power. More than 126 million
water buffalo exist worldwide.
The large, fierce African
buffalo (Syncerus caffer) should not be confused with the
more common and useful water buffalo.
The water buffalo is important to tropical agriculture
because it is a gentle, domesticated animal that provides
power as well as milk and meat, while subsisting on fodder.
It does well in hot, humid climates, and its bulky body, large
feet and slow, steady pace make it particularly useful in
flooded ricefields. Water buffalo can be divided into two
major groups: swamp buffalo and river buffalo.
The swamp buffalo is found in the Philippines (where it
is called the carabao) and other Southeast Asian countries. It
has an ox-like appearance and is gray to slate in color. It is
distinguished by its large, swept-back horns and a white band
across the neck slightly anterior to the brisket.
The river buffalo is more common in India, Egypt, and
eastern Europe. It is usually black and resembles a large milk
cow but is distinguished by its c,>iled horns. The horn is
triangular in cross section from the basal to the middle
portion. River buffalo are better milk producers than swamp
buffalo. In India, there are half a dozen well defined breeds
of river buffalo.
Although the water buffalo is related to the domestic cow
and the American bison, it is not possible to crossbreed them.
Buffalo have 48 chromosomes, while domestic cattle and
bison have 60. The water buffalo’s ability to regulate body
temperature is inferior to that of tropical cattle. The buffaio
has few sweat glands, and its hair is sparse and coarse. It
requires protection from both intense sun and cool winter
winds. Water buffalo enjoy submerging in water or wallowing
in mud during the heat of the day. If arrangements are not
made for the buffalo to have access to a stream or water spray
during the hot season, its health deteriorates rapidly.
The buffalo compares favorably to the bullock in certain
respects, but unfavorably in others. As a draft animal on a
road, the water buffalo is inferior to the bullock. The buffalo
cannot withstand dry heat and direct sun as well as oxen, and
its feet are not as tough. Early castration of males intended for
work not only makes them docile, but results in a neck
conformation that facilitates fitting the yoke. In this regard,
water buffalo are more convenient than bullocks, which do
not have a neck well suited for the yoke if they are castrated
too early.
The same type of harness is used with both the water
buffalo and the bullock. Whereas bullocks are most commonly harnessed in pairs, water buffalo usually work singly
with the single shoulder yoke.
Tests were conducted in the Philippines using six SOO-kg
male cardbdo. Pulling loads
on grass for 2-h periods, each
carabao provided draft power of 0.5-1.3 hp. The animals’
speed of 3.5 km/h remained constant over the test periods
under draft test loads of 40, 60, and 100 kg (88, 132, 220 lb;
or 392,588,980 N). The highest power output occurred while
pulling the loo-kg draft load. At the end of the 2-h, IOO-kg
draft load tests, the animals’ body temperatures were elevated
and they required a rest.”
The water buffalo usually maintains itself by grazing.
Lactating animals are sometimes provided with grain or oil
meal cake.
Water buffalo are subject to the same diseases as cattle:
foot and mouth disease, rinderpest, haemorrhagic sel?ricaemia, and anthrax. They frequently host the larger cam:r::
parasites but exhibit little evidence of their presence. ?~‘ile
productive life of a water buffalo is approximat.ely 6 yr.
1.3.3 Elephants.The elephant is the largest domesticated draft
animal. An adult elephant weighs approximately 3 t. Because
of their great weight, elephants have a stiff-legged walk,
which for a working elephant varies from 3.4 to 3.7 km/h (2.I2.3 mph).*8 As a prime mover, the elephant has a barely
adequate cooling system. Because of its smaller ratio of
surface to bulk compared with other animals, the elephant is
not able to dissipate heat well. In tropical climates the
elephant is usually warked only 3 h in the morning and 3 h
in late afternoon to avoid the hottest pan of the day.19
Research on using elephants for tillage was conducted at
the Neelgaon Farm near Sidhauli in Unuu Pradesh, India.
Using a special elephant harness and pulling a two-bottom
moldboard plow, an elephant easily plowed 1 ha of land 15
cm deep in 4 h. Another animal turned over 2 ha in 4 h with
a disc harrow.*” Elephants can provide draft power of 4-5 hp
and can lift approximately 700 kg. As a beast of burden the
elephant can carry approximately 500 kg. The active life of
an elephant is about 60 yr, but the best work years are
between the ages of 20 and 40. Unfortunately, an elephant
needs a large supply of fodder and t.hus is inexpensive to use
only where fodder is inexpensive. An elephant requires
approximately 125 kg of fresh material and 50 kg of dry
material per day. The Indian amry ration for medium-sized
elephants consists of 6.8 kg grain, 80 kg dry fodder, 180 kg
green fodder, 56 g salt, and 28 g of oil, plus about 200 liters
(50 US gal) of fresh water per day.”
Indian elephants are used for transport and log handling.
Although African elephants are not domesticated, in 1925 and
again in the I95Os, African forest elephants (Loxodonta
afticana cyclotis) were trained f:>r work in the Belgian Congo
(now Zaire).zz Unfortunately, the elephants and their trainers
disappeared during the civil war in the early 196Os.‘j
3.3.4 Hams. The horse (Equus caballus) used for draft is
usually broad and massive. It has a thick neck, heavily
muscled shoulders and legs, a wide chest, and coarse legs. In
Europe and North America, horses used for farming are of
larger breeds and are better fed than those in LDCs. Farm
horses range from 350 to 1,000 kg in weight and I50 to 175
cm in height. The height of a horse is the vertical distance from
the ground to the withers, The withers is :he ridge between
the horse’s shoulder bones (Fig. 1.8). A linear measurement
equal to four inches (10 cm> and called a hand is used to
express the heig:ht of a horse in English-speaking countries;
farm horses range from 15 to 17 hands in height.
Horses are usually put to work when 2-3 yr old and can
continue to work until about age 20. Mares, stallions, and
geldings (castrated males) are all useful as draft animals.
Geldings are quieter and easier to handle than stallions. Colts
are usually castrated as yearlings or 2-yr-olds.
Draft horses are not well adapted to the hot humid tropics.
since the ratio of body mass to surface area limits cooling even
though horses utilize sweating to cool themselves. Horses are
used in the tropical highlands, which are cooler than the
lowlands. However, above 3,000 m (10,OOOft) altitude, horses
develop enlarged hearts and other problems because of the
thin air.
Working horses are fed and watered three times a day.
One-fourth of the horse’s daily feed is given at least 1 h before
work. At midday, after about 5 h of ,work, the horse is watered
and fed another fourth of its daily ration. When the horse is
stabled after the afternoon’s work, it is watered and fed half
its daily ration. The horse should be watered before and after
each meal. The type and amount of feed a horse requires
depend on the work. Horses should be provided with 2.2 kg
1.8. Nomenclatureof a
Point of shoulder
of feedstuff for every 100 kg of body weight (2.2 lb/100 lb
body weight); 1 kg grain and 1.2 kg hay/100 kg is ample for
ordinary farm work. Maize, Wats, and barley are the grains
most commonly fed to horses. Barley should be crushed. Hay
should be of good quality and, if possible, alfalfa hay should
constitute one-third to one-half of the ration. A 650-kg horse
or mule requires 6.5 kg grain and 7.8 kg hay per day. If horses
are turned out to a good mixed pasture during rest time, they
will eat about 50% less hay.
The daily feed requirements of draft horses can be
expressed in tenns of total digestible nutrients (TDN) by the
following equation:
TDN = 0.043 W”.73+ 0.215 H
where: TDN = kg,
W = body weight in kg, and
H = work output in MJ
in English units. the equation is:
TDN = 0.053 W”.7a + 1.27 H
TDN = lb,
W = body weight in lb,
H = work output in hp-h”’
The first term represents maintenance requirements,
while the second term represents energy for work output.
For example, a 500-kg (1100 lb) horse with a work output of
13 MJ/cl requires 6.8 kg (15.0 lb) of TDN per day. These
estimates are in general agreement with the values provided
by Gee ancl McDo~ell.“~
Horses, mules, and donkeys have well-developed shoulders and chests, but weak withers. Collar harnesst.s 01
breastband harnesses are therefore used. Collar harnesses are
requireci for heavy draft work SLICII as plowing, while hreastband harnesses are satisfactory for light work such as pulling
a light buggy. The several types of harnesses for horses,
mules, ant1 donkeys vary according to the implement or
vehicle, the training of the animal. the number of animals
hitched together, and the owner’s idiosyncrasies. Harnesses
are usually made of leather. If properly fitted and maintained,
a good harness can be serviceable for 20 yr,
The following description of harnessing a horse also
applies to mules and donkeys. Harnesses are illustrated for
three situations: single horse with breastband harness (Fig.
1.9, 1.10) and 2:, 5-, and lo-horse teams with collar harnesses
(Fig. 1.12, 1.14, 1.15).
The breastband harness places the load against the horse’s
breast by means of a wide leather strap called the breastband
or breast collar. The traces connect to the implement. Traces
are made from either leather or steel chain. The bridle is the
headgear used to govern the horse. It consists of the bit,
noseband, front, cheekpiece, and throat latch. The bit is made
of steel and is placed in the horse’s mouth. The reins are
leather straps fastened to the bit on one end and held by the
driver on the other. By means of a pull on one or both of the
reins-often ticcompanied by a voice command-the
controls the horse. The reins are prevented from falling to the
ground and becoming entangled in the horse’s legs by means
of a metal ring called a terret, which is shown fastened to the
Blinders are stiff leather pieces that prevent the horse from
seeing sideways and that direct its attention straight ahead.
The blinders prevent the horse from becoming aware of
movement TOthe side. When harnessing a horse, me bridle
is first slipped over the horse’s head, while the bit is placed
in the mouth. The throat latch, which is a strap passing under
the horse’s throat, is then adjusted so that it is snug enough
to prevent the horse from pulling off the bridle, but loose
1 .Q. Simple breastband
enough so as not to bind and cause discomfort. The backstrap
and the neckstrap of the breastband harness support the
breastband at the proper height. Just as a suit of clothes or a
backpack should be fitted to the human individual, a harness
must be fitted to each horse.
The simple breastband harness shown in Figure 1.9
cannot be used to pull a buggy or an implement with a line
of draft high enough to lift the harness off the horse’s back.
A buggy requires an attachment for the shafts and a means to
prevent the buggy from pushing rhc Larness forward into the
horse when descending a hill.
By placing a bellyband on the simple breastband harness,
loads with a higher line of pull can be drawn without lifting
the harness off the horse. A buggy can be hitched to the
harness illustrated in Figure 1.10 by attaching the shafts
(sometimes called thills) to the saddle. A flat leather strap,
called breeching, keeps the buggy from running into the
horse while descending a hill by preventing the harness from
moving forward. The shafts are attached to the saddle, and a
strap secures the saddle to the breeching, so that when the
buggy pushes on the shafts and the shafts on the saddle, the
strap fastened between the saddle and the breeching transfers
the load to the breeching, and this to the animal’s rump. The
crupper goes around the tail to prevent the harness from
sliding off the horse.
The check rein is used when the driver wants to prevent
the horse from lowering its head to graze.
1 .lO. Breastband harness
with bellyband and
Horses, mules, and donkeys need to use collars for pulling
heavy loads (Fig. 1.111. Horse collars are manufactured in
specific sizes to assure proper fit. When fitting a collar to a
new work animal, different sizes should be tried until one that
fits is found. Horse collars come in three types: regular. half
Sweeney, and full Sweeney. The regular is for long, flat,
slender necks; the half Sweeney is for a neck that is a bit
heavier and slightly thick at top; and the full Sweeney is for
a neck very thick at the top. The size of a collar is determined
by its inside length measured from top to bottom. For
example, a size 20 collar measures 20 inches (50.8 cm> from
top to bottom just inside the rim. Small draft horses require
size 16 or smaller, while very large draft horses need size 24
or 1arger.l” Collars are sometimes further characterized by a
measurement of the cross-section circumference at the collar’s
widest point. This measurement is called the draft size.
To fit a collar, the horse is moved forward against a load
until t~hecoliar is firmly against its shoulders. Alternately, a
strong person can pull back on the traces. Correctly fitted, the
collar should allow only sufficient space between the sides of
the neck to pass the flat of the hand.
When the collar is forced back, there should be about 5cm clearance between the collar and the animal’s throat. A
short collar causes a sore neck, chokes the horse by pressing
1.11. Horse collar.
1.12. Harness for a team of
two draft horses.
against the windpipe, and sets the point of draft too high. A
long collar places the point of draft too low and causes
shoulder sores. Once a collar is fitted, it should not be taken
apart each time the horse is harnessed. Instead, the collar
should be kept buckled and slipped over the horse’s head
duri!lg harnessing.
Collars fitted prior to heavy work often become too
too wide-as the horse becomes thinner
from hard work. If this occurs, a collar pad of quilted cotton
should be inserted to improve the fit.
The traces are not attached directly to the collar, but to a
separate steel or steel reinforced rib called a hame. A hame
fits on each side of the collar, and the paii of hames are tightly
strapped, top and bottom, to the outside groove of the collar.
The hame consists of three rings and a metal bolt. The trace
attaches to the bolt, the breast strap to the bottom ring, and
the back strap to the second ring. The rein passes through the
top ring. An ornamental metal ball is usually attached to the
top of the hame.
Figure 1.12 depicts a harness for a typical team of two
horses or mules. The two-animal team is the most common
draft configuration.
Note that the wagon or implement is
pulled forward by the interaction of various connecting parts.
First, the animal pushes against the collar, to which the hames
are attached. Second, the traces, which are attached to the
hames, transmit the pull to the singletrees. Third, the pdi is
transferfed from the singletrees to the doubletree, which is
attached to the wagon tongue.
When the team must hold back a wagon while descending
a hill, the force is transmitted in reverse, since the wagon
pushes the tongue forward. First, the tongue transmits the
forward force to the neck yoke. Second, the force moves from
the neck yoke to the jockey yokes. Third, the jockey yokes
transfer the force to the harness, which moves forward until
the breeching moves into contact with the animal’s rear
When driving a team, the reins are attached to the outside
of the animals, and cross check lines are crossed between the
animals to pr?vide maximum control. The cross check lines
(Fig. 1.13) enable one rein to turn both animals.
When greater horsepower is required, horses and mules
can be hitched in larger teams. In constructing hitches for
multi-horse teams, it is important that the geometry of the
1.13. Team and cross check
hitch be such that 1) the load is equalized so that no animal
can loaf, 2) side draft is minimized, and 3) each animal has as
much space and comfort as possible.L’ A typical 5-horse hitch
is illustrated in Figure 1.14. In this configuration, the retr team
has sufficient air space and the driver has a good view of all
the horses. There is also plenty of room for lines and less
opportunity for crowding and trampling during sharp turns.
The IO-horse hitch shown in Figure 1.15 has an advantage
in that the driver needs to control only the two lead horses.
Since the lead team sets the pace, they should be well
Eveners are made of steel-reinforced wood 5-10 cm thi&
and about 1 m long. In a multi-horse hitch, the singletrees and
doubletrees attach to the eveners. These attach to other
1.14. Five-horse team (left).
1.15. Ten-horseteam
eveners and eventually to the implement. The purpose of the
evener is to balance the forces. For example, the j-horse team
in Figure 1.14 has the forward right and center horses hitched
so that their combined pull is exerted through a doubletree
attacher1 to one end of an evener. The left front horse is
attached to the same evener. Since the left front horse can pull
only half as much as the other two, its singletree a,ttachrnent
to the evener is twice as far from the draft chain on the evener
as is the doubletree from the other two horses (80 cm as
opposed to 40 cm>.
To guide the horse, the farmer uses a pair of reins fastened
to a bit in the horse’s mouth as well as verbal commands. In
North America, common temls are *‘whoa” to stop. “steady”
to move more slowly, “gitty-up” to begin moving forward,
“gee” to turn to the off-side or right, and “haw” to turn to the
near-side or left.
If the horse is working on soft ground, horseshoes are not
necessary. But if the horse is to be driven WI hard roads or
slippery streets, it should be shod.
The blacksmith must
custom-fit each shoe. For ordinary conditions, a plain shoe
without talks and sufficiently heavy to carry the animal’s
weight should be used. Shoes should be reset every 6 wk. If
possible, horses that are kept shod most. of the year should
have their shoes removed for 1 mo and be allowed to work
on soft ground in order to allow the hoof to recover its natural
ZJ.,5 MU/IX A mule is the general term for the offspring of
a horse and a donkey. Actuallyl t!le offspring oi a mare and
a jackass is called a mule, while the offspring t~:fa stallion and
a jennet is called cl hinny. The mule is more valualk,
it i,s larger than the hinny.
The mule is preferable to the horse as ;I work animal
because it is less afflicted by disease and can utilize inferior
feedstuffs. However, it is more discriminating of certain feeds
than the horse. Mules are often chosen over horses for hot,
humid climates, a for terrain requiring steacliness and surcfootedness.
Mules weigh 300-600 kg (6X-1300 lb) and are of‘ variolus
colors. In height they vary from Ii0 to I75 cm. Mules ;ire
harnessed in the same manner as horses. It is not uncommon
to hitch horses and mules together as a team.
Mules are usually put to work at 3-4 yr of age, but they are
at their peak at 6-10 yr. The mule has a long life. Some have
lived to be 70 yr old.
If a mammal’s lifetime is measured by the number of
heartbeats, all have approximately the same life span of 800
million heartbeats and 200 million breaths. The cow and
elephant have the same number of heartbeats per lifetime as
all other mammals. The exception is man, who has three
times as many heartbeats per lifetime as other mamn~dls.*x
1.3.6 Donkqs The donkey is also known as the domestic ass
(E~~uusc~‘nms). The small ass or burro is also known in some
regions as a donkey. The donkey is primarily a pack animal,
and can travel about 30 km/d, but it is also used in some
regions as a draft animal. Like horses and mules, donkeys
must be shod. Males are called jacks or jackasses! while
females are called jennets. Donkeys range in height from
about one meter to the size of small horses. The ass is noted
for its endurance, surefootedness, docility, and ability to
subsist on feedstuffs inferior to those required by horses. As
pack animals, asses carry from SOto 135 kg (110-300 !b) over
distances of 25 to 32 km (15-20 mi) per day.
1..3.7 Camels. Camels are
used primarily
as pack animals“baggers”-but
are also employed for riding and for draft.
There are two species of camels. The Arabian camel ( C,zrnek,l.s
cjrom&zr-iusj has one hump and thrives in the tropics, while
the Bactrian camel of Asia (Camelus hacttia~zms) has two
humps and can live in cold climates. The single-humped
Arabian camel is the anima! discussed here.
Riding. baggage? and draft camels differ in body conformation and qualities, just as sadd!e horses differ from work
horses. The riding camel is an efficient means of communication in remote areas. A riding can& ;kould be slender and
long-legged, with a strong but fine bone structure. A thin,
supple skin and a dropping rump of medium length are
characteristic of a riding camel. The baggage camel should be
robust, heavy. and m,ell furnished with bone and muscle. The
hump should be well developed. Legs should be heavy, and
the hooves should be large and flat. The draft camel has the
same qualities as the baggage camel, since it is used for its
brute strength and ability to work on sandy or loose soil. Draft
1.16. Camel plowing.
camels are used singly or in pairs, and are sometimes yoked
with bullocks or donkeys.*YJ Figure 1.16 illustrates a camel
Most animals regulate body temperature by a metabolic
activity that keeps body temperature nearly constant even
when they are engaged in physical activity. An increase in
physical activity produces excess heat, which must be
dumped to maintain bodv temperature.
Excess heat is
dumped through evaporative cooling by panting or sweating.
Evaporation is an effective means of cooling, particularly
under low humidity, but the process consumes body moisture.
The camel is one of the few large mammals (the giraffe is
another) that allows body temperature to fluctuate 3-10 “C
during the day. Passive heating and coo!ing conserve a large
amount of water.g” The camel’s regulation of body temperature is andlogou~ tcJ the regulation of house temperature
during summer in the temperate zone. For example, the
desired house temperature may be 25 “C. Rather than turning
on the furnace during the cool early morning, the house is
allowed to heat slowly by passive heating from rising outside
air temperature as the sun rises in the sky. If the house
temperature rises above the desired 25 ‘C, it may be necessary
to dump excess heat from the house by turning on an air
conditioner. Had the house been heated to 25 “C in early
morning and the temperature kept constant, it would have
been necessary to :urn on the air conditioner before noonanalogoils to sweating or panting in an animal to dump excess
Prior to the American Civil War, camels were used for
transport in the southwestern United States. The U.S. Army
imported 74 Arabian camels between 1856 and 1857. These
animals were used primarily in Texas, New Mexico, and
California. In 1861, a private company imported 20 Bactrian
camels from Central Asia. These animals were used to
transport salt in Nevada.
Camels are ruminants. They often prefer to eat shoots or
twigs rcirher than grass. A general rule is that camels should
be allo\\-ed at least 6 h/d for foraging, and another 6 h for
rumination. Where conditions do not permit foraging, camels
can be fed the same feedstuff as that fed to cattle. Table 1.3
lists daily rations for baggage camels.
The camel is noted for its ability to endure long periods
without water. Whenever possible. however, it should be
waterer’ iiaily. A camel drinks up to 35 liters daily. A camel
deprivtci of water for a long time may drink up to 90 liters (24
US gal) of water at one time ! Males, females, and castrated
males art: used for draft work. The castrated male is preferable
if castrati<)n does not occur before the animal reaches full size
at 4-6 VI-,
Camvis used on the plains are usually long-legged and
rangy, and may attain 2.12 m height at the withers. Camels
used in rough and hilly areas are smaller, heavy-boned, and
Table 1.3. Rations for camek3’
Camel type
Walking camel
No grain, but some salt
Trotting camel
Working baggager
20 lb (9 kg) straw, 4 lb (1.8 kg) gram,
some salt
Working baggager
30 lb (13.5 kg) straw, 6 lb (2.7 kg) gram,
some salt
10 lb (4.5 kg) grain each watering day,
some salt
only 1.75-2 m high. Baggage camels can carry 150-300 kg at
a speed of 4 km/h for 24 km/d.
The camel can plow at a speed of about 2.5 km/h but is
usually worked no longer than 6 h/d--4 h in the morning and
2 h in the afternoon. The rate at which a camel can plow has
been reported variously as 11-20 hi/ha when plowing to a
depth of 16 cm (6.3 in>.32 The difference is probably due to
soil variance, plowing depth, type of plow, method of
hitching, condition of the camel, and skill of the operator.
A saddle is used for pulling a cart and quite often for
plowing. The saddle consists of a wooden frame with pads
that rest on &her side of the animal’s backbone. Arches
clearing the backbone and on each side of the hump are
fastened to the padded vertical frame. A single girth holds the
saddle in position. The shafts attach to the sides of the saddle
for pulling a cart.
A belly yoke is used for plowing. If the yoke were placed
on top of the saddle, the camel’s height would place the line
of draft at too steep an angle. A padded single yoke in front
of the hump is often used instead of a saddle. Alternately, long
traces can be attached to the padded single yoke in front of
the hump. The length of the traces is such that the plow point
may be up to 5 m behind the camel. This extraordinary trace
length is necessary to obtain a proper line of draft.
Plowing with a camel usually requires two people-one
to lead the camel and one to handle the plow. The camel is
controlled by a nose peg and head rope.
Camels can be put to heavy work from about 6 to 20 yr
of age. If properly managed, camels may live up to 45 yr.
1.3.8 Llamas. The llama (Lamaglama) and the alpaca (Lama
paces) are American relatives of the camel. They are raised
and used in the Andean countries at high altitudes (2,6004,600 m; 8,000-14,000 ft).
The llama is raised for wool, meat, and use as a pack
animal (Fig. 1.17). The alpaca is smaller than the llama and
is raised chiefly for its wool. It is seldom used as a pack
animal, since it cannot carry as much as a llama. Llamas reach
maturity at about 2 yr and weigh 85-120 kg.
Only males 3-7 yr old are used as pack animals. Castrated
males of 4-6 yr are preferred. The average mature male llama
can carry 35-45 kg (75-100 lb) over short distances. On
1.17. Pack llama.
caravan treks, however, drovers limit loads to about 25 kg (55
lb) to reduce fatigue.
Cargo carried by llamas is usually grain, potatoes, or salt.
Bags are half-filled with cargo and draped across the llama’s
back. A rope secures the bag to the llama. The top of 11llama’s
back is about 1.2 m high, so llamas are loaded while standing,
unlike camels. Although a g;)od pack llama can travel 40 km/
d over a period of 3-4 wk, a typical llama caravan traveling 6
h/d between morning and late afternoon grazing will cover
-:bout 300 km in 22 d, including 7 rest days.jj This is an
average of 20 km/d over arid plateau, mountain trails, and
high valleys.
1.4 Rotary power
Animals are best suited for work by pulling. To operate
machines such as irrigation pumps, threshers, and grinding
mills, however, rotary power is required. Sweep powers and
tread mills are devices that can convert animal power to rotary
Sweep power (sometimes called circular horsepower,
power-gear, or a horse-gin) is used in many countries to
power pumps, threshers, and sugarcane presses (Fig. 1.1.8).
Many sweep power machines are wasteful of the draft
animal’s energy, since the units utilize roughly cut gears and
1 .18. Horse with sweep
made from automotive axle
and differential.
and wheel
.~ L..I71,
for machine
lo be
poody lubricated high-friction bearings. Manufactured units
are more efficient because of machined gears and pinions,
and proper lubrication.
Treadmills are made in sizes ranging from those powered
by a dog to those requiring several oxen or horses. ,A treadmill
consists of a slatted floor or belt that is inclined and mounted
on bearings. The animal walks forward and lifts its weight
against the force of gravity. The floor of the treadmill should
have a pitch of one vertical unit for each four horizontal units.
Thus, the animal constantly lifts one-fourth its weight. The
faster the animal walks, the greater the power output.
Because of the number of bearings and sliding surfaces in
these machines, it is imperative that they be well lubricated.
1. Baumeister T, ed. (1987) Marks’ standard handbook for mechanical
engineers. 7th ed. McGraw-Hill Book Co., New York. p, 9-209, 210.
2. Food and Agriculture Organization of the United Nations (1985) FAO
production yearbook. Vol. 38. FAO Stat. Ser. 61. Rome.
3. Food and Agriculture Organization of the United Nations (1972) The
employment of draught animals in agriculture. Rome.
4. Bailey L H (1908) Cyclopedia of American agriculture. The MacMillan Co.,
London. p. 217.
5. Hopfen H J (1969) Farm implements for arid and tropical regions, FAO
Agric. Dev. Pap. 91. Food and Agriculture Organization of the United
Nations, Rome. p. 10.
6. Williamson G, Payne W (1965) An introduction to animal husbandry in
the tropics. 2d ed. Longmans, Green & Co., London.
7. Van Bath S B H (1963) The agrarian history of Western Europe, AD 5001850. Edward Arnold Publication, London.
8. Ibid.
9. Marks L S. ed. (1951) Marks’ mechanical engineers’ handbook. 5th ed.
McGraw-Hill Book Co., New York. p. 1080.
10. Brady S (1945) Bioenergetic and growth. Reinhold Co., New York.
11. Desowitz R S (1977) The fly that would be king. Natural History 86(2):
Fell 1977.
12. Juarez F, Duff J B (1977) Changing supply and demand patterns for
power tillers in the Philippines. Paper No. 77-03. Philippine Society of
Agricukural Engineers, Manila.
13. Matthews M D P, Pullen D W N (1975) Cultivation trials with ox-drawn
implements using N’damd cattle in the Gambia. National Institute of
Agricukurdl Engineering, S&c&, England;
14. Shiv Chandler Lal Premi, (1979) Performance of bullocks under varying
conditions of land and climate. Thesis No. AE-79-5. Asian Institute of
Technology, Bangkok.
15. Williamson and Payne, op. cit.
16. BalisJ (1964) A study of farm power uni!s: their performance and cost.
Aiklhabad Agricultural Institute. Allahabad, India.
17. Lantin R M 11984) Energy expenditure and work capacity of the
Philippine work carabao while pulling loads. MS thesis, Ilniversity of the
Philippines at Los Barios, Ldguna, Philippines.
1X. Falvey J L (1987) An introduction Io working anin&.
Melbourne. p. 162.
MPW AWdia.
19. Ibid.. p. 164.
20. Sin& S B (1955) The elephant comes into farming. Indian Farming S(2):
May 1955.
21. Singh H (19X0) Domestic animals. 2d ed. Kational Book Trust, New
Delhi. p. 114-116.
22. Grzimek B (1957) Where Africa’s elephants become tame. Pages 136155 inNo room for wild animals. Thames and Hudson Publishing, London.
23. Personal communication from Dr. John King of the International
Livestock Center for Africa, Addis Ababa, 1I May, 1982.
24. Brody S, Cunningham R (1936) Comparison between efficiency of horse,
man, and motor, with special reference to stze and monetary economy.
Growth and development. XL Univ. of Missouri Res. Bull. 244. p. 45-50.
25. Goe M F, McDowell R E (198O)Animal traction, guidehnes for utilization.
Cornell University, Ithaca, New York.
26. Horse and Mule Association of America (no date) Collar, hames and
harness fitting. Leaflet 276. Chicago.
27. Horse Association of America (1928) Horses, mules, power-profit.
Leaflet 190, Chicago.
28. Gould S J (1982) The panda’s thumb. W.W. Norton Sr Co., New York.
p. 303-304.
29. Mukasa-Mugerwa E (1981) The camel (Camelus clmme&rrius):
bibliography review. The International Livestock Center for Africa, Addis
Ababa. p. 70-79.
30. Langman V A (1982) Giraffe youngsters need a little bit of maternal love.
Smithsonian 122(10):102.
31. Mukasa-Mugetwa, op. cit., p. 42.
32. Ibid., p. 79.
33. West T L (1981) Llama caravans of the Andes. Natural History 90(12X62-
Lampe K J (1982) Animal traction and mechanization. Paper presented at
a Seminar on Mechanization of Small Scale Farming, Jun 1982, Hangzhou,
People’s Republic of China. 30 p.
Makhijani A, in collaboration with Poole A (1775) Energy and agriculture
in the Third World. Ballinger Publishing Co., Cambridge, Massachusetts.
168 p.
Munzinger P (1982) Animal traction in Africa. German Agency for Technical
Cooperation, Eschbom, Federal Republic of Germany. 470 p.
Singh H (1980) Domestic animals. 2d ed, i%itiORdBook Trust, New Delhi,
India. 156 p.
Stout Li A, Myers C A, Hurand A, Faidley L W (1979) Energy for world
agriculture. FAG Agric. Ser. 7. Food and Agriculture Organization of the
United Nations, Rome.
The word “trxtor” derives from the Latin trahere, meaning “to
draw.” The first tractors were designed only for draft, but later,
devices such as belt pulleys and power-take-off (PTO) shafts
were added so that the power unit could furnish rotary powei
as well AS draft power. Tractors can be categorized by the
following characteristics.
= Means
of traction (Itracklxyer or wheeled)
l Type of paver
plant (diesel> q’ark ignition, or steam)
* Number of driving wheels (one. two. or four)
* Horsepower Cfrom few to several hundred)
0 Operator’s position (riding or walking)
Tractors are generally categorized into three groups: farm
tractorsl compact tractors, and pedestrian tractors. Farm
tractors include tracklayers as well 21swheeled tractors. The
FAO data in Table 1.~Iinclude ail riding tractors and tracklayers of 8 hp or greater that are used for farm work. In North
America, only tractors of more than 20 hp are normally
considered farm tractors. Riding tractors less than 20 hp are
called compact or garden tractors. Pedestrian tractors are also
called w4king tractors or tillers. They range from 2.5 to 15 hp
and are controlled by the operator, who walks behind.
2.1 Engine power
Most +ricultural tractors have four-stroke cycle engines. In
:I four-stroke cycle engine. the piston must traverse the length
of its cylinder in a cycle of four .<trokes--intake, compression,
power, and eshaust--for each power stroke.
In a two-stroke cycle engine, each piston traverses the
cylinder twice for each power stroke. At the start of the first
stroke, fuel is taken into the cylinder and the air-fuel mixture
is compressed before the end of the stroke. The work
performed in two strokes (the intake and compression
strokes) of the four-stroke cycle occurs within a single stroke
in the two-stroke cycle. At the start of the second stroke,
burning and expanding gases push against the piston face,
providing engine power. Toward the end of this stroke, the
gases of combustion are exhausted. Thus, the second stroke
fulfills the functions of both the power and the exhaust strokes
(the thirci and fourth strokes) of the four-stroke cycie engine.
In small gasoline engines for pedestrian tractors (10 hp or
less), the average two-stroke cycle engine provides a better
ratio than the average four-stroke
cycle engine. The fuel efficiency of the two-stroke cycle
gasoline engine, however, is poorer in this horsepower range.
Where flotation is a consideration, such as working in a
ricefield, or where a man must carry an engine-powered piece
of equipment such as a sprayer or mower, two-stroke cycle
gasoline engines are used because of their smaller size. One
of the chief problems encountered when using small, twostroke cycle gasoline engines is that, since the lubricating oil
is usually mixed with the gasoline, spark plug fouling is
Two-stroke cycle diesel engines are sometimes used on
farm tractors of more than 100 hp. In a diesel engine, the
initiation of combustion is controlled by the injection of the
fuel. Since superchargers and exhaust scavengers are used on
large, two-stroke cycle diesel engines, fuel efficiency is better
than in small engines.
The average fuel requirement for a farm tractor with a
standard transmission and a four-stroke cycle engine of more
than 20 hp may be estimated if the maximum PTO hp is
known. To estimate average fuel consumption, the following
formulas can be used.
Liters gasoline/h = 0.227 x (max PTO hp at sea level)
Liters diesel/h
= 0.1665 x (max PTO hp at sea level)
The above estimates are based on the average of the
“Varying Power and Fuel Consumption” portion of the
Nebraska Tractor Test, rather than on fuel consumption at
maximum power (see Appendix D).
Altitude affects power. An internal combustion engine, in
which air is sucked into the cylinders by the pistons, creating
a partial vacuum during the intake stroke, is called a naturally
aspirated engine. A gasoline engine requires an air-to-fuel
ratio by weight of 15:1. The ratio varies from about 19:1 to 8: 1
depending on engine speed and fuel setting (lean or rich). At
high altitudes, air is less dense, containing less oxygen than
at sea level. Human beings and draft animals are similar to
naturally aspirated engines because they respond to thinner
air by delivering less power. The reduction in power of a
naturally aspirated internal combustion engine can be described by the equation:
hp, =
where P = air pressure in inches of mercury
T = temperature in degrees Rankin
(Rankin = degrees Fahrenheit + 459.67)
x = altitude
s = sea level
In Peru, farming occurs over a wide range of altitudes. A
60-hp tractor sold in Lima (sea level) will not deliver 60 hp on
the nulnerous high-altitude farms in the country. Table 2.1
reveals the difference in a tractor’s PTO hp in various
agricultural regions of Peru.
The human body partialiy compensates for high altitude
by increasing the number of red corpuscles, thus increasing
the oxygen-bearing capacity of the blood. Similarly, the
addition of a turbocharger or supercharger to a tractor’s
engine can return the horsepower output to its sea level
Table 2.1. Effect of altitude upon tractor power in Peru.
Altitude (m)
Lima (sea level)
La Molina (coastal desert)
Power of 60-hp
tractor (PTO hp)
Ticlio (mountains)
Huancayo (mountain valley)
San Raman (high jungle)
Yurimaguas (Amazon Basin)
rating. The advancement of spark nrning in a spark-ignited
engine also provides a slight improvement of power output
at high altitudes.
2.2 Tractor
The word horsepower is somewhat confusing when applied
to tractors, because there are various terms that refer to tractor
horsepower, namely, engine brake, PTO, belt, and drawbar
Engine brake horsepower does not include the losses that
occur between the engine flywheel and the wheels or PTO
shaft. For this reason, engine brake horsepower is represented by larger numbers than other forms of tractor horse
power. Engine brake horsepower measurements are sometimes made with the fan, water pump, and alternator connect~ed to an auxiliary source of power so that the engine
under test will indicate a high horsepower on the dynamometer. Automobile engines are often tested in this Fashion.
Have you ever wondered why a passenger car engine is
rated at several hundred horsepower, while a farm tractor
with an engine of the same +?e may be rated at less than 100
hp? Belt horsepower or PTO horsepower is the net power
available at the PTO shaft, and is measured while the tractor
is stationary. Belt horsepower or PTO horsepower is always
less than engine brake horsepower. The power required by
oil and coolant pumps, gear losses, and other power losses
between the engine crankshaft and the belt pulley or PTO
shaft represents the difference between engine brake horsepower and PTO horsepower. Maximum belt or PTO horsepower is numerically the highest reading taken from the
complete tractor. Farmers use a belt pulley or PTO to power
such implements as irrigation pumps, forage blowers, and
hammer miils. The relative performances of such implements
can be visualized by comparing maximum PTO horsepower.
Drawbar horsepower is a useful measure of horsepower.
since it provides a direct comparison with draft animals, as
well as with other tractors used for draft work. Drawbar
horsepower, however, varies with changes in soil conditions,
Drawbar tests are dually
tire size, and tractor weight.
performed on tarmac.
In the United States, the Nebraska Tractor Tz:;ts are the
srandard farm tractor tests. Nebraska tests are currently
conducted only for tractors of 20 hp or greater. A typical
Nebraska Test report is shown in Appendix D. Engine brake
horsepower tests are usuaiiy conducted in accordance with
the Standards of the Society of Automotive Engineers (SAE) in
the United States, or with Deutsche Industrie Norm (DIN)
standards in Germany.
Tractor engines are fueled by diesel, gasoline, kerosene,
or liquefied petroleum gas (LPG!. The cost and availability of
fuel often determine the type of engine used. Most farm
tractors produced today
are diesel powered.
In some
countries where gasoline or diesel is not readily available,
pedestrian tractors frequently use kerosene.
2.3 Single-axle
pedestrian tractor
2.1. Single-axlepedestrian
Pedestrian tractors or tillers are usually classified as single-axle
or double-axle units. Single-axle units (Fig. 2.1) have one
powered axle, while double-axle units have two powered
When single-axle tractors are used for draft work such as
pulling a plow or a cart, the drive wheels are attached to the
axle. For rotary tillage, the drive wheels are removed and tines
are fastened to the axle. The tines both till the soil and propel
the tractor forwarci. A retarding bar at the rear of the tractor
controls travel speed and depth of tillage. To till deeper, the
retarding bar is placed deeper into the soil to provide
increased drag. As a result, forward motion is reduced and the
rotating tines make a greater number of slices per area of earth
tilled, thus working the soil deeper.
Single-axle tractors are usually equipped with wide cage
wheels and a moldboard plow in order to accomplish primary
tillage in ricefields, which are usually flooded at plowing time.
Secondary tillage of a ricefield is usually accomplished with
a comb harrow, a puddler, or both.
The major components of a single-axle tractor are the
frame, engine, transmission; and axle. The frame is a
weldment fabricated .from structural or formed steel shapes.
The transmission case is usually an integral part of the frame.
The engine is air-cooled. The type of fuel and the engine
manufacturer are determined by economics.
The most
popular single-axle tractors use spark ignition engines in a
range of 5-10 brake horsepower.
The transmission performs two functions. The primary
function is to reduce the engine crankshaft speed of approximately 3600 rprn to an axle speed of approximately 50 rpm.
The transmission’s secondary function is to provide one or
more speed reduction ratios, thus allowing slow speed for
field work and greater speed for highway travel. A V-belt is
generally used instead of a chain or gear drive for the first
speed reduction step from the engim, since it not only can
transmit power, but is used as an engine clutch. The operator
uses a belt tightener as a clutch. The belt tightener is moved
away from the belt to disengage the engine. The belt shps in
the engine sheave so that no power is transmitted. A V-belt
should operate at high speed and low tension, while a roller
chain and sprocket drive should work at low speed and high
tension. Double sheaves are often used on the V-belt drive
of the single-axle tractor to provide two speed ranges. One
set of sheaves provides field speed; the other set provides
highway speed.
The transmission consists of the transmission case and the
gear sets or chain and sprocket sets it encloses. The
transmissions on most single-axle tractors make two speed
reductions in the transmission case. The transmission case is
liquid tight and contains oil to lubricate the gears or chains.
Bearings at the bottom of the case support the axle.
Three types of wheels are used on pedestrian tractors:
pneu,matic tire, steel upland, and paddy. Lugged pneumatic
tires are used where the tractor is to be used on dry fields, or
roads. In many parts of the world, steel upland wheels are
preferred because they are less expensive than pneumatic
tires. A typical steel upland wheel for a single-axle tractor is
75 cm in diameter and 20 cm wide, with 13 blades. The padcly
wheel is preferred for work in wetland fields. A typical paddy
wheel for a single-axle tractor is 45 cm in diameter and 50 cm
wide, with 12 blades per wheel. Not only does the wide
paddy wheel provide better flotation than the narrower steel
upland wheel, but it performs an acceptable job of puddling.
In the temperate zone, it is undesirable to smear the soil
by the action of a wheel, since impervious layers adversely
affect plant development. Soil consisting of crumbly partic!es
allows oxygen intc the soil.
A ricefield is entirely different. To retain water in the
ricefield and to provide a favorable environment for the rice
roots, the bottom of the field is worked into an impervious
layer of small particles. This process is called puddling. The
bottom of a ricefield is oxygen-deficient, but the rice plant has
the ability to oxygenate the roots through the stem. Most,
weeds do not possess this unique feature, and thus are
eliminated by drowning.
Tractor weight affects performance. In general, a heavy
tractor can convert more of its engine horsepower into
drawbar pull than can a light tractor. In a ricefield, however,
a lightweight tractor has an advantage because it has better
flotation and is more easily maneuvered by the operator, who
may be up to his knees in mud.
Most single-axle tractors are not equipped with steering
clutches or a differential on the axle. The operator turns by
grasping the handle and pulling sideways. Both wheels are
Iwiving, but one is forced to skid, and the turn is accomplished. This type of turn requires extra effort, but single-axle
tractors are not heavy. One model, LandmasteP, has a
reversing device for making a left turn, whereby actuation of
a handlebar lever reverses the axle rotation. The left-hand
wheel moves rearward, while the right-hand wheel remains
stationary, since it is secured’ to the axle with a nonreversing
clutch. The tractor thus makes a leftward pivot about the righthand wheel.
Figure 2.2 shows the relationships between drawbar pull,
slip, and horsepower for a typical single-axle pedestrian
tractor. Note that the tractor weighed 175 kg (385 lb) for the
2.2. Drawbar horsepower
and slip vs draft.’
2.0 1
-Slip (%)
Draft (kg)
test and that steel upland wheels were used. The gasoline
engine was rated at 7.25 maximum brake horsepower.
Some pedestrian tractors can perform a variety of functions Figure 3.3 is an exploded view of a single-axle tractor
such as the LandmasterrM or the IRRI PT-5 with tools and
A recent development from the Philippines is a range of
floating rotary tillers for wetland rice production.
machines-the Turtle Tiller from an floilo manufacturer and
the Hydrotiller series from IRK1 (Fig. 2.4i, have single or twin
hull floats, respectively, that help support the front-mounted
high-speed rotor. These machines have been rapidly accepted in Southeast Asia because they can work in ricefieids
with water so deep (~e.g.,0.5 rn) to the hardpan that a singleaxle tractor cannot be used, and even a water buffalo and
plow would find it hard going.’ They perform the functions
of simultaneously puddling, leveling (hydrotiilers only),
2.3. Single-axle pedestrian
tractor and attachments.
2.4. Hydrotiller, a floating
rotary tiller (IRRI twin-hull
Weight with engine
Horsepower (brake hp)
diesel or gasoline
195 cm
75 cm
Rotor diameter
and width
325 rpm
Rotor speed
Field capacity,
first pass (puddling
and incorporating) 1.8 ha/8 h
weeding, and green manure incorporation. They can worl
right to the edge of the field and even trim levee sidewalls
which is valuable benefit for weed control and roden
management. A drawback is that these are single-purpost
machines that are not balanced for transport purposes on hart
surfaces. For transport between sites, att~achahie outrigge
wheels, a trailer, or a sled is needed.
2.4 Double-axle
pedestrian tractor
The double-axle tractor (Fig. 2.5) is usually larger, morn
powerful, and more expensive than the single-axle tractor. i
is used primarily for rotary tillage. It also serves as the po\\-e
unit for a multitude of uses, from timwing trailers to pumping
water. One axle propels the machine from the front, while the
rear axle acts as a rotary tiller. There is a large variety 01
features for double-axle tillers. The remarks in this section
refer primarily to the 8- to :IS-hp modeis commonly used fol
farming in Southtiist Asia.
A double-axle tractor is two tc) three times heavier than ;
single-axle tmcror. However, since doul~le-axle tractors arc
equipped with steering clutches and the forward speed of tht
drive wheels is independent of the rotor speed, the units art
2.5. Double-axle pedestrian
270 kg
Weight with engine
1.5-l 0 km/h
Travel speed
Field capacity
1.2-l .5 ha/8 h
Horsepower (brake hp) 8-l 2
33 cm
Tiller diameter
75 cm
Tiller width
often less tiring to operate than single-axle tractors. In some
double-axle tractors, the tiller shaft rotation is such that the
blades tend to move the tractor forward at a high speed but
are prevented from doing so by the drive wheels, which move
the tractor forward at a speed selected by the operator.
Tractors such as the Troy-bilt in the United States are easy to
control when tilling unflooded land, even with one hand. To
provide sufficient traction, these tractors are usually rearheavy, with most of the weight being carried by the driving
Double-axle tractors used in flooded ricefields perform
better when the direction of rotation of the rotor shaft is the
same as that of the drive wheels. The tiller blades assist in
moving the tractor forward.
Double-axle tractors have various transmission arrangements. A common arrangement includes six forward speeds,
two reverse speeds, and two rotor shaft speeds. Disc clutches
are usually used instead of a V-belt and idler combination.
Since the double-axle tractor is usually of greater horsepower
than the single-axle tractor, the stronger (though more
expensive) plate clutch provides better service than does the
V-belt and idler type clutch.
2.5 compact
Compact tractors (often called garden tractors> are 4-wheeled
tractors of less than 20 brake hp. In the USA, compact tractors
are generally used more for lawn mowing than for agricuLura1
work. A typical compact tractor is illustrated in Figure 2.6.
Two compact tractors designed primarily for agricultural
work are the Self Help?‘” and the Agro-UtiF”. Tests at Kansas
State University revealed that these tractors, equipped with
single 12-in (30-cm) moldboard plows, could plow 1 ha of
wheat stubble in 11-14 h. This figure includes time for turning,
adjustments, and stoppages due to clogging.”
The range of hours required to plow a hectare was caused
by differences in soils (which ranged from clay loam to silty
clay loam), the moisture content of the soil, and wheel
weights. The Agro-litil“” was equipped with a Wisconsin
Model S-12D air-cooled gasoline engine, which develops 12.5
brake hp at 3600 vrn. The Self HelpT” tractor had a Wisconsin
Model EY44W, which develops 10.5 brake hp at 3600 rpm.
The governed engine speed for these tractors was 2800
rpm. Plowing was conducted in second gear at approximately
2.6. Typical compact
(brake hp)
350 kg (772 lb)
A 00 cm
Travel speed
Field capacity
of Deere
8.50 x 12 rear
6.50 x 8 front
1.5-l 2 km/h
(0.9-7.5 mph)
1 ha/12 h
& Company
4 km/h (2.5 mph).. The fuel consumption during piowing
ranged from 21.5 to 42 liters gasoline/ha (2.3-4.5 U.S. gal/
acre). Most compact tractors use gasoline engines, but a few
use diesel.
Examination of the data in Table 2.2 illustrates the general
principle that additional weight on a tractor’s driving wheels
will enable the tractor to convert additional engine power to
Table 2.2. Draft, drawbar horsepower, and wheel slip vs rear wheel
weight for Agro-Utilm.a
Static weight on
rear wheels (kg)
Wheel slip
Drawbar power
a Basic tractor weight on rear wheels was 451 kg, including weight of operator,
water in tires, and concrete wheel weights. Drawbar tests conducted on firm soii
with moisture content of 6.1% (dry basis).
b Figures in parentheses are values in N.
’ Engine overloaded and not up to governed
2.7. Compacttractor with
additiondl drawbar horsepower. In other w-ords, the limit of
engine power is reached when excessive slippage occurs.
Some compact tractors have the engine over the rear wheels
for additional weight (Fig. 2.7).
Without tools, tractors are useful only for transportation.
Standards enable manufacturers of various compact tractors
to use interchangeable implements. The American Society of
Agricultural Engineers (ASAE) has established standards for
drawbars, 3-point hitches, and 2000 rpm PTOs for compact
Farm tractor
The FAO data in Table 1.1 specify as farm tractors all riding
tractors used for farm work. Since I have used the North
American convention of designating riding tractors of less
than 20 hp as compact tractors, I shall use the term farm
tractors for riding tractors of 20 hp or more. When referring
to farm tractor horsepower, maximum PTO horsepower is
used unless another horsepower measurement is specified.
The State of Nebraska-home
of the famous Nebraska
Tractor Tests-requires the University of hk?bnSkd
to test at
least one tractor of each model sold in the state. Results are
published. A farmer can then use the test data to decide which
tractor is best for his situation.
The Nebraska Tractor Tests originated during the early
days of farm tractors, shortly after World War i. A Nebraskan
farmer who was also a member of the Nebraska legislature
purchased a tractor that did not perform up to its advertised
claims. The farmer-legislator therefore introduced a bill
providing that no farm tractor could be sold in Nebraska
unless it had been tested at the llniversity of Nebraska. and
unless the manufacturer had made spare parts available in the
Since no tractor manufacturer can afford to produce a
special version of its tractors for sale in Nebraska, the
Nebraska Tests became the standard performance tests for
farm tractors sold in North America. A typical Nebraska Test
is shown in Appendix D.
A rubber-tired farm tractor like the one shown in Figure
2.8 is generally more desirable than a tracklayer (Fig. 2.‘)),
since it is less expensive, has high rodd and field speed, can
be operated on asphalt highways without~ damaging t~he
highway surface, and costs little to maintain. A tracklayer is
preferred when farming is conducted on steep slopes or
where very loose soils or organic soils require a high draft
from a small tractor,
The rear wheels of f&111 tractors ~UKI most compact
tractors can be btilked indepezdctntly if desired. The foot
brake pedal is sp!it so that if only the right rear wheel is to be
braked, the driver pushes against the right-hand sick of the
pedal. To brake the rear left wheel. the left side of the pedal
2.8. Two-wheel drive farm
80 hp
3,200 kg
5,000 kg
(max PTO)
(no ballast)
(max ballast)
1.520 km/h
of Deere
& Company
400 cm
200 cm
200 cm
16.9 x 36 rear
7.5 x 16 front
2.9. Tracklaying farm tractor.
Power (max PTO)
Length of track on ground
Speed, forward (max)
256 hp
287 cm
273 cm
30 km/h
of Caterpillar
5.7 m
330 cm
Width of .track
62 cm
Inc., Peoria,
is depressed. By pressing equally against the fxe of the split
foot brake pedal, both re;u wheels xe txsked. Independent
rear wheel brakes are ;\ great aid in making short turns and
steering in muddy fields. Most farm tractors do not have front
To convert engine horsepower into draft, high frictial is
teyuirecl at the interface of the soil and the part of the tire
contacting the std. An extreme exan~ple of the principle is 3
rubber-tired tractor on ice. Although the tractor has a
powerful engine, there is little friction. Therefore, the wheels
spin, and draft and drawbar horsepower are 7cr(:. Traction is
uaaiiy oiuined
by increasing the weight on the drive
wheels. When the soil no longer supports the wheels, they
sink further into the soil, and rolling resistance increases while
draft decreases.
A tractor with front-wheel assist (Fig. 2.10) is ;I ktsic twowheel drive tractor equipped with powered front wheels. The
front wheels of most front-wheel assist tractors are driven
through the same transmission as the rear wheels, The front
wheels are driven at a speed that provides ;1tire speed equal
to or about 1.05 times the speed of the rear tires. A few twowheel drive tractors that have been retrofitted for front-wheei
2.10. Farm tractor with
front-wheel assist.
of Deere&Company
xssist use hydraulic motors to driv,c1the front wheels. Mcchanical drive is usuaily better than hydraulic drive, since the
front and rear tire speeds remain in synchronization better
with mechanical drive. All front-wheel assist tractors can he
operated in either the two-wheel drive or the front-wheel
assist mode with all four wheels powered.
On a hard surface a properly weighted two-wheel drive
tractor will perform as well as the same tractor with frontwheel assist and the same gross weight with regard t,o wheel
slip and drawbar power. In soft field conditions. the frontwheel assist tractor can develop greater drawbar power than
the two-wheel drive tractor. A study in Nelxaska used XI 80hp farm tractor equipped with front-wheel assist mcl operated
in both the powered and nonnowered front,-wh4 modes on
disked silty clay loam wheat stubble and on the fame soil after
it had been plowed to a depth of 20 cm and disked again.”
Tractor gross weight was kept at 5,105 kg (,1,1,255 lb) in all
tests. When in two-wheel drive. 74% of the weight WIS carried
by the rear tires. In the front-wheel assist mode, the tractor
weights were shifted so that 59?6 of the weight was carried by
the rear tires. The tests showed that tractor weight distribution
is very important when in the two-wheel drive mode: the drive
wheels must carry most of the t,ractor’s weight to reduce wheel
slip. In the front-wheel assist mode, weight distribution is not
very important. On the firm surface of disked wheat stubble,
the maximum clrawbar power was about 65 hp for both
:ilodes, but on the soft surface of plowed and disked wheat
sttibble the tractor produced about 10% more clrawbar power
when in front-wheel assist mode. The advantage that a frontwheel assist tractor offers over a two-wheel drive tractor is
dependent upon field conditions and the ballast weight
distribution of the two-wheel drive tractor.
A basic difference between wheeled tractors designed for
mo-wheel drive and four-wheel drive is the location of the
tractor’s center of gravity relative to the axles. The two-wheel
drive tractor has two-t~hirds of the tractor weight on the rear
axle so that the,weight is on the driving wheels; a four-wheel
drive tractor places two-thirds of the weight on the front axle
so that, under a heavy draft load, all tires will be equally
loaded because of “weight transfer” due to the geometry of the
hitching of the tractor to the load (see Fig. 2.11~.
Worldwide standards help t.o make farm tractors versatile.
Standards for three-point hitches, rear PTOs, and hydraulic
couplers, and specifications for hydraulic cylinders for implements make it possible for implements from various manufacturers to match with tractors made by other manufacturers
throughout the world (Fig. 2.12). Farm tractor three-point
2.11. Four-wheel drive farm
Power (max PTO)
325 hp
Weight (no ballast)
121.250 kg
Weight (max ballast)
15,500 kg
Speed, forward
5-30 km/h
of Massey-Ferguson,
a business
of Varity
650 cm
245 cm
330 cm
350 cm
16.9 x 38 rear,
7.5 x 16 front
2.12. Rear 3-point hitch and
PTO of a farm tractor.
hitches are classified as Category I, II, III, or IV depending
upon tractor power. Table 2.3 lists important dimensions and
hitch lift capacity of the ASAE standard.5 By using hitch pin
and hitch stud adapters, it is possible to use an implement of
a lower category on a tractor of a higher category. For
example, a category I implement can be hit.ched to a category
II tractor by using adapters.
The two lower hitch links are powered by a hydraulic
cylinder inside the tractor chassis. Lift height is controlled by
a lever, which is usually mounted on the side of the fender or
cab wall next to the driver. The upper link is not powered and
Table 2.3. Important rear 3-point hitch dimensions.
in hp (kW)
20- 45 (15-35)
40-l 00 (30-75)
80-225 (60-l 85)
180-400 (135-300)
Upper link
hitch pin diameter
in inches (mm)
314 (19)
1 (25)
1 i/4 (32)
1 3/4 (45)
Lower link
hitch stud diameter
in inches (mm)
718 (22)
1 1!8 (28)
1 7/‘16 (36)
2 (51)
Lift force
of hitch in
lb (kN)
1040-2340 (4.6-l 0.8)
2080-4810 (9.3-21.7)
4160-8060 (18.6-36.1)
’ 6890-12,610 (31 .O-56.6)
ser~cesonly to keep the implement stable as the lower links
lift or lower the implement. Mosi farm tractors have rear
three-point hitches that can also be set in a draft control mode.
In draft control, the three-point hitch will keep constant the
amount of draft force exerted by an implement such as a plow
by lifting the implement to reduce draft when the draft limit
set by the driver is exceeded. If the draft falls below the
setting, the hitch automatically lowers the implement further
into the soil to increase the draft. Draft control will prevent
stalling a tmctor when plowing a field with varying soil
resistance, but in soil with great variation in resistance, a
tractor in draft control mode will plow shallower than desired
under some conditions and deeper under others.
Some three-point hitches are designed so that, by means
of linkage, a downward force from the lower lift arms can be
transferred to a trailing implement such as a disc harrow.
Fann tractors come equipped with both a rear threepoint hitch and a swinging drawbar hitch. Depending upon
the implement, the swinging drawbar may be removed from
the tractor when using the three-point hitch, and the lower
and upper links of the three-point hitch may be secured out
of the way when using the swinging drawbar. A drawbar hitch
consisting of a steel bar with several drawbar pin holes at
midsection and a stud at each end to fit the lower links is also
commonly used with a three-point hitch. To meet [email protected] standards, tractor drawbars must withstand a minimuln stat,ic load
at the hitch point ranging from 3.34 kN (750 lb) for a 20 dwvb
hp tractor to 24.5 kN (5500 lb) for 500 dwb hp.”
Important dimensions of the ASAE standard 7 for rear
PTOs and swinging drawbar hitches for farm tractors are listed
in Table 2.4. The direction of rotation of all farm tractor real
PTOs is clockwise when standing behind the PTO and facing
in the direction of forward travel. Some tractors have both
type I(540 rpm) and type 2 (1,000 rpm) rear PTOs so that both
540 rpm and 1,000 rpm implements may be used with one
tractor. It is not possible to operate an implement designed
for 540 rpm by a tractor with a 3,000 rpm PTO or vice versa.
Some farm tractors are equipped with front three-point,
hitches and PTOs. In general, the dimensions of the front
three-point hitches are the same as those of rear three-point
hitches, but there is no general agreement yet on the direction
of rotation and spline dimensions for front PTOs.
Table 2.4. Important rear PTO and drawbar hitch dimensions.
diameter in
inches (mm)
1 3/8 (35)
1 3/8 (35)
1 314 (45)
Hitch pin
diameter in
End of PTO
shaft to hitch
pin hole in
inches (mm)
Height of
above ground in
inches (mm)
314 (19)
314 (19)
1 l/4 (32)
14 (356)
16 (406)
20 (508)
13-22 (330-559)
13-22 (330-559)
13-22 (330-559)
To convert the energy developed by a tractor’s engine into
useful draft, sufficient friction must be developed between the
driving tires and the roadbed or soil surface. If the frictional
force is too small, excessive wheel slip and an attendant loss
of power result. To increase drawbar pu11,the driving wheels
are usually weighted and equipped with lugged tires, which
grip the soil.
Tmctor drive tires are made in four basic classes designated by the tire industry with an R code: R-l, regular
agricultural tire; R-2, rice and cane tire; R-3, sand and industrial
tire; and R-4, industrial lug. A class of low pressure tires
sometimes referred to as a “terra-tire” does not have an R
R-l (regular agricultural) is the basic agricultural tractci
drive tire with widely spaced lugs for general farming.
R-2 (rice and cane> is the same tread design of R-l except
it has lugs that are twice the depth of R-l lugs in order to
provide traction in very muddy conditions. Because of lug
height, tires with R-2 tread are less stable and wear less well
on the road than R-l tires.
R-3 (sand and industrial) has closely spaced buttons in
place of the traditional lugs. The R-3 tread depth is 60% of the
depth of R-l lugs. The tires are used on sandy soils and
conditions such as golf courses where minimum lug penetration is necessary.
R-4 (industrial) lugs are wider, more closely spaced, and
only 70% of the lug depth of the R-l tread. The tire is used
for abrasive conditions and is often seen on tractors used in
highway construction.
The low pressure terra-tire has a wide tread that provides
a large “footprint” for low ground pressure and good flotation.
The low inflation pressure and the tire’s construction provide
high shock a,bsorbing capability. The tires can be identified
by their very low ratio of tire diameter to width.
Front tires for two-wheel drive farm tractors come in
three basic classes, F-l, F-2, and F-3.
F-l (single rib) has a single rib.
F-2 (regular agricultural) is available in the greatest
number of sizes Andyis the one most commonly seen on twowheel drive tractors.
F-3 (industrial multiple rib) is the front tire analogous to
the R-4 tractor drive tire.
Tractor tires are available in both bias and radial constnrction. Most tractor tires are of the bids type. Radial tires have
slightly improved traction, resist sidewail torque buckling,
and last longer than bias tires; but radial tires are usually more
costly than bias tires. A radial tire is identified by an R after
the tire size, which is molded into the tire sidewall.
Drawbar pull is developed when the tire lugs penetrate
the soil surface and tend to shear the soil. Different soils have
different shearing strengths. The amount of moisture in the
soil also affects shearing strength. The shearing strength of the
soil depends on the cohesion of the soil particles and the
weight of the wheel on the soil. Increasing the weight of the
wheel interlocks the soil particles more tightly, and the
shearing resistance is increased. Drawbar pull can increase to
a point where the shearing resistance of the soil is no longer
great enough to withstand the increased force from the tire
lugs. At this point, wheel slip becomes excessive. Actually,
there will always be some wheel slip, and the greater the
drawbar pull, the greater the wheel slip.
Maximum drawbar pull is obtained when wheel slip is as
high as 50-70%. Since high slip causes high loss of power,
however, most farm tractors are weighted and tired so that
wheel slippage does not exceed 15%.
Since wheel slip and loss in forward speed are in direct
proportion, wheel slip can be easily calculated in the field.
First, a mark is made on one of the tractor’s drive wheels.
Second, with the tractor pulling an implement at working load
or working depth, the distance traveled by the tractor in 10
revolutions of the wheel is marked off on the ground. Third,
the load is disconnected, and the number of revolutions of the
wheel over the same distance is counted. Since there is no
drawbar pu!l during the second part of this test, there will be
less wheel slippage, and fewer revolutions (revs) are required
to travel the distance. Wheel slip can be calculated as follows:
% wheel slip
10 revs - no-load revs x , o.
10 revs
Rolling resistance of a wheel tmust first be overcome
before the wheel will move (Fig. 2.13). Rolling resistance
occurs primarily because the weight of the tractor causes the
wheel to sink into the ground. As a result, when the wheel
is moved forward, it must run up the small incline formed as
it moves ahead. A heavily loaded wheel on soft soil sinks in
deeply, and the rolling resistance increases. Subjec: to the
same weight, a tire with a large diameter will geoerally have
less rolling resistance than a tire with smaller diameter, a wide
tire less rolling resistance than a narrow tire, and a tire with
low pneumatic pressure less rolling resistance than the same
tire at high pressure.
The generalities delineated above refer to machines
operating on soil. On a rigid surface such as concrete, where
no sinkage occurs, decreasing tire pressure may in fact
increase rolling resistance because of increased tire deformation. As illustrated in Figure 2.13, there is a constant trade-off
between increasing weight to reduce slip and decreasing
weight to reduce rolling resistance.
Traction aids are sometimes used with wheeled farm
tractors to improve draft capability in difficult conditions. A
2.13. Orawbar power loss
vs tractor weight.
study of traction aids for a typical 45-hp farm tractor was
conducted at the University of Guelph, Ontario, Canada.”
Tmction aids were tested on five land conditions: dry and
loose, cultivated sandy loam; damp, cultivated medium loam;
wet and green stubble on medium loam; frozen alfalfa sod on
medium loam; and sparse hay aftermath on wet heavy clay.
Figure 2.14 presents the findings of the study.
Soil conditions is one of the primary variables affecting
traction, but the relative effectiveness of the various traction
aids remains in the same ranking for all five soil conditions.
The Canadian tests revealed that traction aids increased
drawbar pull up to 2 l/2 times that obtained from the
unballasted, 2-wheel drive farm tractor. The tests further
showed that tire chains do not irnprove traction on sandy soils.
On frozen sod, chains provide about 17% additional drawbar
pu!l. About 6% additional draft can be obt.ained on the other
soil conditions.
Large diameter tires improve traction. By increasing tire
diameter from 13.6 x 28 to 14.9 x 28, traction is increased by
14%. The 13.6 x 28 tire has a loaded radius of 59.7 cm, while
the 14.9 x 28 has a loaded radius of 62.2 cm. The larger tires
in this test showed least traction improvement in dry sandy
2.14. Performance of
traction aids on a 45hp
2-wheel drive farm tractor.
13.6 x 26 tires
Sofubon-filled 13.6 x 26 hms 6 chains
Dud s&tion-6lW
1 Soluton
‘-. hlkd
13.6 x 26 tires
13 6 x 26 hre$ 6 half lrscks
(2165 ke)
(1616 kg,
1’ 6
loam and greatest improvement in sparse hay aftermath on
heavy clay.
Unwkighted dual tires will provide about l/3 more
traction than unweighted single tires. The unweighted duals
exhibited least traction improvement on dry sandy loam and
the greatest improvement on sparse hay aftermath on wet
heavy clay.
Half-tracks in this test were endless steel tracks 50 cm wide
fitted over each rear drive tire, and a spring loaded idler wheel
mounted ahead of each rear wheel. The half-!.racks doubled
the drawbar pull on all five soils.
Weight is the most common and one of the most effective
traction aids. If weight is added, drawbar performance can be
increased by half. Dual tire equipped tractors and half-track
equipped tractors also produce greater drawbar pull if weight
is added to the drive wheels.
As illustrated in Figure 2.14, a farm tractor equipped with
solution-filled single tires can pull a greater load than the same
tractor equipped with dual tires without weights. Weight can
be added to a tractor by bolting weights onto it, by placing dry
ballast such as lead shot inside the+ires, or by filling the tires
75-90% full with a solution of calcium chloride and water. The
calcium chloride keeps the water from freezing. If a pneumatic tire is filled to more than 90% with a water solution, the
tire will lose its performance characteristics, since -tiY;:teris not
Pedestrian tractors respond to additional weight and
various wheel and tire configurations in a manner similar to
four-wheeled farm tractors. Figure 2.15 illustrates the effect
of various types of wheels and tires on the draft of a singleaxle pedestrian tractor operating on upland clay soil with a
moisture content of 22%. A ballasted weight of 286 kg was
used for the tests. The normal weight of this tractor is 112 kg.
The tires v+.ith town and country tread were 6-13.00, 6-ply
pllrurilatic, while those with bar tread were 5-12.00, 2-ply
pneumatic. Both sets of tires were inflated to 145 kPa (21
An examination of Figure 2.15 reveals that heavily ballasted pedestrian tractor operation on upland soil provided
draft with the least amount of slippage when equipped with
pneumatic tires with the town and country tread. At 150 kg
of drawbar (dwb) pull, the town and country tires had a wheel
tires, town and country
tires, bar tread
cage wheel
Ford DNT spade wheel
slip 1%)
2.15. Wheel slip vs drawbar
pull for a single-axle
pedestrian tractor?
pull (kg)
shp of approximately 25%, while the tractor equipped with
lowland cage wheels had a wheel slip of 40%. Although the
draft was identical in each case (150 kg), the tractor with the
greater wheel slip had slower forward speed. The drawhar
horsepower of the tractor with the lower wheel slip was
higher, since
dwb hp = (speed x draft) x (a factor)
Thus, the tractor equipped with town and country tires
provided a higher drawbar horsepower than the tractor
equipped with lowland cage wheels.
Traction in conditions providing poor flotation, such as
flooded ricefields, presents a different problem. In such
conditions, weight is a hindrance, since additional weight
sinks the tractor deeper into the mud, thus increasing its
rolling resistance. This situation calls for a lightweight tractor.
Lowland cage wheels for a pedestrian tractor and wheel
strakes for a farm tractor will also improve traction and, in the
case of tilling flooded ricefields, will aid in puddling the soil.
Oversized tractor tires inflated to a low pressure will also aid
flotation and traction. Researchers at Centro fnternacional de
Agricultura Tropical (CIAT) have found that the performance
of 60- to 80-hp 2-wheel drive tractors working in mud can be
improved by using oversized tires.‘” By purchasing the rims
normally used with the next largest class of tractor, it is
possible to install the high lug rice and cane tires of sizes,23.1
x 26 or 23.1 x 30. These tires are inflated to 34.4 kPa (5 [email protected]
No water ballast is added to the tires, and no rear wheel
weights are attached. These low-pressure, oversized tires
provide much better flotation and mobility in the mud of
ricefields. Disadvantages of this system are the high cost of
the large rims and tires, and the need to space the tractor
fenders upward so they are not struck by the tires. If a tractor
equipped with oversized tires is used for dryland work, the
tires must be inflated to normal air pressure. When inflating
tractor tires to only 34.4 kPa (5 psig), it is necessary to use a
water manometer to measure tire pressure, since the common
tractor tire gauge is not accurate at low pressure.
A rotary tiller has negative draft and may actually push the
tractor forward. A rotary tiller as used on a double-axle
pedestrian tractor or a farm tractor is usually designed so that
the tine action moves the tiller fot,ward as it rotates. Thus the
tractor can be lightweight, since it serves only as a chassis and
steering mechanism for the engine. This is one of the primary
reasons for using rotary tillage in flooded ricefields.
2.7 Single-wheel
2.16. Single-wheel
pedestrian tractor.
The single-wheel pedestrian tractor (Fig. 2.16) is powered by
a 5-brake hp, air-cooled, gasoline engine and is used primarily
as a self-propelled cultivator and a power unit for drawing a
small trailer. Although the unit is characterized by its large,
single drive wheel, the machine actually has two wheels in
contact with the ground during cultivation. The second wheel
is a small guide wheel in front of the tractor. The guide wheel
provides depth control and resistance to side thrust when
cultivating with a single curved shovel, which throws earth to
the side.
2.8 Motorcycle
The motorcycle tractor (Fig. 2.17) is primarily a transportation
vehicle that can be used as a small agricultural tractor. The
two-wheel drive motorcycle tractor is preferred to the onewheel drive model because the former provides better
traction. When used with an outrigger wheel to provide
stability and operator comfort, the unit is actually a tricycle
tractor. The motorcycle tractor is useful in siash-and-burn
agriculture (shifting cultivation), where it is necessary to work
around trees. It is possible to add weight to some models by
filling the center portions of the wheels with water or fuel.
2.17. Two-wheel drive
motorcycle tractor.
9 hp at 8,000 rpm
Power (brake hp)
85 kg (187 lb)
Weight (no ballast)
2 cycle gasoline
Engine type
gasoline and oil, 2O:l ratio
200 cm
80 cm
6.70 x 15.2 ply @ 24 kPa (3.5 psig)
0.8 - 60 km/h
Speed, forward
200 kgf (1960 N, 440 lb)
Drawbar pull
The motorcycle tractor is not suitable for ricefield cultivation because the engine is set low to the ground and would
be damaged by water or mud. Furthermore, it is impossible
to use cage wheels with the unit.
2.16. Plowing with cable.
drawn plows.
In the ‘i3ritish Isles during the 18OOs, some plowing was
accomplished by using steam-powered winches to draw
plows across a field as shown in Figure 2.18.” That is why we
refer to the grades of wire rope as plow steel. In the early
19OOs,plowing by cable systems was carried out in Californian sugar beet fields and Hawaiian sugarcane fields.
Several types of cable systems were used during the
1800s. The most successful was the double engine and cable
method. Two steam tractors equipped with wicrhcs w-cm
aligned on opposite ends of a field. Each winch drum
contained 300-420 m of cable. A plow, harrow, or other t,ool
was attached to the cable. While one engine played out the
cable, the other engine wound it in, thus drawing the plow
across the field.
When a pass across the field was completed, both steam
tractors were advanced a distance equal to the width of the
gang of plows. Two-way plows were used so that the furrows
were thrown properly regardless of dim&on in which the unit
was drawn.
In England, master-slave rigs were used which required
only one steam tractor with a winch and a double cable. The
slave was a heavy wheeled vehicle equipped with a large,
anchored pulley. The steam tractor (master) was set up on
one side of the field and the pulley (slave) on the other. The
endless cable would be wrapped several turns around the
winch drum. As the master winch rotated in one direction, the
cable drew the implement across the field.
When the
implement reached the slave, the master stopped the winch,
and the operator of the implement reversed the direction of
the tools. Both master and slave moved forward a distance
equal to the width worked by the implement. The operator
of the master then engaged the winch in reverse, thus drawing
the implement back toward the master.
The cable system used in the 1800s utilized the heavy,
massive steam engines of the day as a source of drawbar
for tillage. With the cable system it was possible to
plow boggy lands where heavy tractors would sink. The land
was not compacted by a heavy tractor, and the entire brake
horsepower as measured at the winch was available for
drawing the implement. There were also disadvantages, the
primary one being the high investment cost. Also, because of
the length and weight of the cables, the system was restricted
to small fields of rectangular shape.
A third type of cable system was the roundabout system.‘* In this system, the steam engine and winch were either
positioned in one corner of the field with anchors deployed
to hold large pulleys placed in the other corner; or the engine
was located in the center of one side of the field while four
anchors with pulleys were placed in the corners of the field.
The cable was run around the field’s periphery, and the
implement was drawn back and forth across the width of the
field. After each pass, the two anchors directly in line with the
implement were moved d distance equal to the width of the
Cable systems utilizing a single cable wound onto a winch
and side-mounted on a four-wheel farm tractor are in use in
European vineyards today. The system makes it possible to
cultivate very steep slopes with mechanical power. The
tractor, with its side-mounted winch, drives up the slope
following the contour of the land. The implement to he drawn
is placed at the bottom of the slope. When the tractor is in
position, the operator of the implement takes the free end of
the cable, pulls it down the slope, and attaches it to the
implement. The tractor driver then engages the winch and
draws the implement and its operator up the slope. The
tractor moves across the slope to a point between the next pair
of trellises, and the procedure is repeated.
A winch and cable system using a pedestrian tractor has
been adapted for use in LDCs. The system is called the Snail
tractive syst.em.i3 The Snail system consists of a self-propelled
winch that looks like a pedestrian tractor, a 30-m cable, and
a modified ox-drawn implement. The system requires two
operators. One operator drives the self-propelled winch
forward, stops it, engages the winch, and draws the tool
toward the winch. The second operator guides the tool as he
would using oxen. Since one operator rests while the other
is working, fatigue is relieved.
The Snail uses a 3-brake-hp gasoline engine as a power
source. The unit is able to achieve a draft of 400-500 kgf (3.94.9 kN, 880-1100 lb) at a cable speed of about I.5 km/h. A
sprag plate acts as an anchor and prevents the lightweight selfpropelled winch from moving toward the tool. The cable
from the Snail is near the ground and parallel to it, so some
adjustment to the hitch point of the ox-drawn implement is
required, because the line of pull from an ox yoke to the
implement is at a steep angle.
Nylon rope was used for cable in the early tests, but it was
unsuitable because of excessive stretch and short life. Furthermore, the sudden release of energy and the whip of the
rope when it breaks is very dangerous and can cause serious
injuries t.o equipment operators. Steel cables are now utilized
almost exclusively.
If fossil fuels become more expensive, cable systems
powered by electric motors-either by battery or direct power
be economically feasible in some agricultural
1. Throngsripong M, Phongsuprasamit S, Buyawanickul S (1974) Design
and testing of a small power tiller. Project Report A743. Khon Kaen
University, Thailand.
2. Villaruz M S (11986)The floating power tiller in the Philippines. Pages
173-178 in Small fxm equipment for developing countries. International
Rice Research Instit:ne, P.0. Box 933, Msnila.
3. Larson G I-I, Jensen J C, Schirld V L (1976) Evaluation of small 4-wheel
riding tractors for developing countries. ASAE Paper 76-IOl4. American
Sncietv of Agricultural Engineers, St. Joseph, Michigan.
4. Bashford L (1985) Axle power distribution for a front-wheel assist tractor.
Trans. Am. Sot. Agric. Eng. 28(5):1385-1388,
5. American Society of AgrIcukurai Engineers (1985) Three-point free-link
attachment fcr hitching impIements to agIiCulNm1wheel tractors. Pages
133-135 in ASAE standards. 32d ed. St. Joseph, Michigan.
6. American Society of AgricuIturaI Engineers (1985) Operating requirements for tractors and power take-off driven implements. Pages 112-113 in
ASAE standards. 32d ed. St. Joseph, Michigan.
7. American Society of AgricuIturaI Engineers (1985! Rear power take-off
for agricultural tractors. Pages 107-110 in ASAE standards. 32d rd. St.
Joseph, Michigan.
8. Southwell P H (1954) An investigation of traction and traction aids. Trans.
Am. Sot. Agric. Eng. 7(2):190.
9. lnternationai Rice Research Institute, Agricultural Engineering Department (1977) Semiannual progress repon no. 24. P.O. Box 933, Manila. p. 23.
10. Johnson L, Alfonso D D (1974) A continuous rice production system.
Info. Bull. 2-E. Cenrro lnternacional de Agricuitura Tropical, Cali. Colombia.
11. Ellis L W, Rumely E A (1911) Power and the plow. Doubleday, Page &
Co., Garden City, New York.
12. Fussel G E (1952) The farmers’ tools. Mayflower Press, London.
13. Crossley C Pi,Kilgour J (1378) Field performance of a winch-powered
cultivation design in Central Africa. J. Agric. Erg. Design 23385396.
American Society of Agricultural Engineers (1983) AgricuIturaI engineers
yearbook. St. Joseph, Michigan.
Branch D S, ed. (i978) Tools for homesteaders, gardeners and small scale
farmers. Rodale Press. Emmaus, Pennsylvania.
Kline D E, Bender D A, Le Pori W A, Schueller J K (1985) Optimization of
automated cable-drawn tillage systems. ASAE Paper 85-1521. American
Society of Agricultural Engineers, Chicago.
Sullivan H D (1988) Role of the U.S. tractor industry in O.E.C.D. testing.
ASAE Paper 881509. American Society of AgricuIturaI Engineers, St.Joseph,
Michigan. 30 p.
Visagie A (1977) Tractor performxice. Eng. Ser. B.3/1977. Department of
Agriculture. Technical Services. Siiverton, Transvaal, South Africa.
Wahlen, D J 11988) Rating of engines for outdoor power equipment. ASAE
Paper 881527, American Society of Agricultural Engineers, St. Joseph,
Michigan. 14 p.
Westley S 8, Johnston B F, eds. Proceedings of a workshop on farm
equipment innovations for agricultural development and rural industrialization. Occasional Paper 16. Institute for Development Studies, University of
Nairobi, Nairobi.
It is in the agricultura! prod,uction system where land, vagaries
of nature, energy, tools, and machines are brought together
to grow food and fiber. For an agricultural production system
to produce crops in a dependable and economical manner,
the various components must be complementary. It is not
easy to obtain a good relationship at the interface betwrcn
mechanical devices requiring uniformity, land, and plants
with biological diversiry, but it is not difficult to mismatch rhe
elements and degrade an agricultura! production system. On;:,
must understand the agricultural production system before
recommending a tool or machine for that system.
Agricultural production systems, cropping systems, soil,
and soil compaction are discussed in this chapter.
Climate, soil, and
farming systems
Climate and soil conditions vary enom~ously throughout the
world, and farming systems successful in one region sometimes prove disa,strous in another. A certain amount of
regional prejudice concerning farming techniques is therefore
quite understandabie. For example, the techniques used in
the soils of Illinois cannot be successfully duplicated in
Latosols of West Africa. Similarly, the evenly spaced rains of
the northeastern IJnited States provide dramatically different
farming conditions from the monsoons of western India.
Because of differences in soils, rainfall patterns, telllperdture, and social structr~lre throughout tht? world, three primary
types of agricultural prociuction systems have developed:
shifting cultivation, polyculture, and monoculture. ‘Mechanization varies according to the agricultural production system
When faced with an agricultural system foreign to one’s
experience, it is wise to learn how it evolved. it is equally
important to consider the advantages and disadvantages of
the system’s adaptation to the specific conditions where it is
Shifting cultivation is a farming system in which a plot of land
is cultivated for several years, after which it is temporarily
abandoned and another plot is cleared and cultivated.
not under cultivation, the first plot is alloxved to rejuvenate.
The rest phase is usually longer than the growing phase. The
temporarily abandoned land is returned to cultivation when
its fertility is restored, or sooner if population pressure makes
new land unavailable. About 36,000,OOOkm’ under shifting
cultivation are currently producing food for 8% of the world’s
people. Shifting cultivation is most extensively practiced in
Africa but is also common in South ,Ameriq Oceania, and
Southeast Asia.’ Shifting cultivation as a method of farming
developed naturally in response to the need to produce f&d,
but without the benefit of soil replenishment by commercial
fertilizers, manure, or alluvial cieposition.
Shifting cultivation was employed by North American
pioneers during the 18th and 19th centuries. As farmers wore
out the soil, they packed up and moved westward to virgin
kdnd. Evennlally, the lack of new land, and improved land
husbandry nearly eliminated shifting cultivation in North
America. It is stilt practiced today, however. in drylancl
fann..!g areas. Wheat growers in the dry areas east of the
Rocky Mountains, where annual rainfall is 300 mm, fallow half
their land in order to conserve moisture. This pattern of
shifting cultivation is dictated by insufficient rainfall. The
farmer annually shifts half his field from wheat to fallow, and
the other half from fallow to wheat. During a field’s falkjw
year, its groundwater is recharger!.
Today, shifting agriculture 1s practiced mostly in the
tropics. -rht2 shifting agric&ure farming system and its
variations are sometimes referred to as slash and burn,
alternate husbandry, citemene system, bush fallow rotation,
land rotation, recurrent cultivation, and swidden cultivation.
In returning fallow land to cultivation in traditional
sh,ifting agriculture, the bush is cleared of vegetation by the
use of axes, knives, and fire. The lancl is then prepared for
planting with a minimum of tillage. The hand hoe disturbs the
soil veq little. The surface soil is sometimes heaped into small
mounds, and several compatible plants, such as maize, yam,
or okra, are planted in each mound. In other cases, an entire
field will be planted to a single crop, such as maize. The
cultivated crop will be weeded as long as this is no more
iaborious than clearing a new site.
The traditional shifting agric&tire system does not result
in excessive erosion because
1. the land is without vegetative cover only after a burn;
2. clearing is usually not done in unbroken tracts of land
over an entire watershed;
3. the root systems, which are not consumed entirely by
the burn, stabilize the surface; and
4. once the first crop is established, the soil remains fairly
well covered.
It does appear that repeated cycles of cropping followed
by fallow periods too short for the ecological balance of the
system can result in severe erosion.
Rotations representative of those in use under shifting
cultivation in equatorial Africa are shown in Table 3.1.
To determine the effect of shifting cultivation on soil, we
must consider separately the systems in forests and in
savannas (grasslands). Studies in equatorial Africa show that
soil erosion is very low under forest fallow, a bit higher under
grass fallow. and very high on cultivated land.
Organic matter in the soil increases during the Follow
period, depending on the state of vegetative cover. It is
estimated that in a typical forest regrowth, the annual production of litter and root materials can be as high as G-8 t/ha. In
grass fallow, the annual amount of plant material added to the
soil does not exceed 1 t/ha, since the annual growth is less and
the aerial parts of the vegetation are lost during the burns.
Table 3.1. Typical crop rotation for shifting cultivation.
1 millet
2 guinea maize
3 cassava
4 6-10 yr of fallow 3-20 yr of fallow
millet and legumes
millet and legumes
millet and legumes
5 yr of fallow
3-10 yr of
A study’ in equatorial West Africa, found that in a forest
. more nutrients accumulate in standing vegetation than
in soil-nitrogen
increases annually by 60 kg/ha in the
vegetation and by 30 kg/ha in the soil; and
trees, with their deeper root penetration, are able to
pump nutrients from the subsoil to the topsoil.
In a savanna fallow, the nitrogen increase is approximately 10 kg/ha per yr in soil and 25 kg/ha per yr in the
When the population density exceeds 25 persons/km?,
population pressure tends to extend the cropping period and
shorten the fallow period. This upsets the ecological balance
of inciigenous shifting cultivation systems, resulting in lcwer
yields and soil degradation. Such a system is exploitative,
since more soil nutrients are removed than the system can
replace. Because of overpopulation, the rational use of
fertilizers and other forms of crop and soil management must
be instituted if the food grown per capita is not to spiral
downward to an inadequate level.
The land tenure system in Africa encourages shifting
cultivation. The individual is frequently less inclined to make
long-term agricultural improvements, since the land is owned
by the entire cammunity. Unlike farmland in North .i\merica,
which is owned by an individual or corporation and can be
used by the owner as he wishes, band in mar:y parts of Africa
where shifting cultivation is practiced is owned by the tribe
and doled out by the chief and his advisors. Although this
practice results in a fairly stable social system, the only
investment in the farm is labor itself.
Land tenure far’ors certain types of agricultural systems. In
North America, private ownership Favors long-term investment in fertilizers, drainage systems, and other investments to
increase crop yield. In equatorial Africa, on the other hand,
the land tenure system, which is part and parcel of the social
system, encourages a shifting type of agriculture with little or
no capital investment.
It is not easy to mechanize shifting cultivation as it is
practiced in forest regions. New approaches must be explored. Mechanization in savannas is easier because there are
not as many roots and stumps in the ground, and not as many
trees to dodge. Minimal tillage, coupled with the rational use
of selective herbicides, is necessary to exploit the benefits of
mechanization in forested areas. In addition, gradual selection and controlled tree cutting to permit the use of machine;);
in straight plots between a grid of permanent trees may prove
Shifting culti\=ation must employ elements of
polyculture and agri-silviculture. Agri-silviculture is a system
in which trees are planted and raised in combination with
crops. In Myanmar (Burma), where the practice of raising
trees with crops on the same land has been studied and
reported, agri-silviculture is referred to as tat~~~ti.
Specific conditions allowed farmers even in prehistoric
times to modify the micrqclimate and move from a system of
shifting to permanent cultivation. The chinampa system in
Mexico utilized muck from canals surrounding the fields as
fertflizer for the fields. The muck, containing decaying
organic matter and minerals, renewed essentials nutrients and
soil tilth. Meanwhile the canals controlied the water table in
the fields. Along the shores of Lake Titicaca, a system of raised
beds known as catneliones was devised to counter flooding,
drought, waterlogging, and frost damage. The raised beds
ranged from 20 to 75 cm above the water, 4 to 10 m wide, and
up to 50 m long, with canals between the beds. Lake Titicaca
is in the tropics but at an altitude of 3803 m, so there are warm
days but sometimes frost at night. The average seasonal lake
level fluctuation is 60 cm, so the low-lying lake plain is often
flooded. The raised beds surrounded by water modified the
microclimate to reduce frost damage, while the height of the
beds prevented waterlogging or flooding of Ihe crops but
ameliorated drought conditions so that potato, oca, and
quinua could be gro\+n3
Polyculture is a cropping system in which two or more useful
plants are grown on the same land. Variations within the
system are multiple cropping, mixed cropping, intercropping,
relay planting, interplanting, and interculture.
Mrdfipie cmpy%r~gis the growing of more than one crop
on the same land in ‘1 yr. For example, buckwheat may be
planted after harvesting peas. Roth crops are grown as
monoculture crops, but they are planted and harvested within
1 yr.
,Mixed cropping is the growing of two or more crops
simultaneously and intermingled, with no row arrangement.
Intercropping is the growing of two or more crops in
alternate rows! for example, maize alternating with soybean.
Rehy planting is the practice of interplanting of the
maturing crop with seeds or seedlings of the following crop.
(If the flowering period of one crop overlaps that of the other,
the practice is intercropping, not relay planting.)
Znterfkmting is the practice of planting a short-term
annual crop with a long-term annual or biennial crop. Oats
and alfalfa, for example, are commonly interplanted in the
temperate zone.
Intercz&ure is the cultivation of one crop underneath a
perennial crop, such as rice under coconut palm.
Although polycultural practices were utilized to some
extent in North America before World War II, mechanization
and the advent of herbicides tended to favor monoculture.
Polyoulture is the dominant farming system in many areas of
the tropics, where the degree of mechanization and the use
of agricultural chemicals relnain low.
It is more difficult lo conduct experiments in a poiycukural
cropping system than in a monocultural system. One study
makes the following observation.
What does emerge from a consideration of the literature,
however, is the realization that most of the supposed advantages
or disadvantages of polyculture are poorly documented. Experiments were generally run over a limited range of environmental
and cultural variables and insufficient data are presented to
conclude whether a specific mechanism was indeed operating.
Adequate characterization of the soils in the experiments was
also generally lacking.4
Polyculture is the typical farming system in traditional
communities in the tropics. If the food output of these
communities is to ii?crt?dSe7the polyculturat farming systems
in use must be improved or altered. Polycutture provides a
stability of yield that is crucial to many farming communities.
Kass sums up the advantages and disadvantages.
the literature generally indicates that polyculture is beneficial. However, the choice of crops and other environmental
variablss will, to a considerable extent, determine whethe: the
practice is advantageous in specific situations. Assuming that
the experimental work carried out thus far represents an adequate sample of the situations in which polyculture is practiced,
it can nonetheless be concluded that definite advantages over
monoculture exist. In terms of withdrawal of nutrients from the
soil, economic return, improvement of the nitrogen status of the
soil-plant system when one of the crops is a legume, and greater
stability of yields over time, the benefits of polyculture are clear.
With regard to ease of harvest and other mechanized operations,
polyculture offers some problems, but recem research aimed at
reducing these difficulties has been surprisingly successfuL5
This successful application of mechanization to polyculture was a system in Illinois, which had been mechanized
before the polycultural system described (soybean and sorghum in oat) was instituted.
Mechanization of polycultural farming systems under
shifting agriculture in the tropics is not accomplished easily.
In fact, it is probably not economically possible to mechanize
shifting cultivation unless other ccnditions affecting the
agricultural system also change. An evaluation of farming
systems in sub-Saharan Africa revealed that the movement of
farmers from foreSt fallow to bush fakm to grass failow to a
permanent annual cropping system was due to economic
incentives to produce more food. Successful mechanization
using animal or tract,or power did not occur before the grass
fallow phase. The. study made several other observations:
Population growth and access to markets were the main
determinants of agricultural intensification.
a The transition from the hand hoe to the anitnal-drawn
plow was profitable only at higher farming intensities.
It was not possible to use the tractor to accelerate the
evolution of farming systems to permanent cultivation
Lack of animal-hLlsbandry~~or mechanical skills was only
a short-run constraint to the use of animal or tractor
High output prices accelerated the pace of intensification and mechanization, provided that they were transmitted to the farm gate.”
Monoculture is a cropping system in which fields of single
crops are cultivated. Although it is the predominant agricultural sy-stem in the temperate zone, monoculture i,s also
practiced in large areas of the tropics. in general, it is easier
to mechanize planting. pest management, and harvesting by
gron/ing one crop at a time. Furthermore, clinratic and
economic factors often so favor a particular crop that there is
little opportunity or financial advantage in a system other than
The wheat belt of North Ameri,ca and the
irrigated ricelands of Southeast Asia are good examples of this
In monocultural farming systems, one or more crops per
year may be grown. For example, in North America there is
only one annual maize crop, while in the Philippines there are
often two rice crops. In both instances, the crops are grown
under monocultural practices.
Monoculture lends itself to mechanization, since only one
plant type is involved. Mechanization requires uniformity.
The man with a hoe does not require straight and uniform
rows, but a maize planter using a tractor requires an unobstructed field with uniform soil condition.
Although only one crop per year is grown in most
monocultural systems, it is important for soil tilth that crops
be rotated. Rotation refers to the practice of not growing the
same crop in a given field every year. With the exception of
the cultivation of wetland rice, rotation should be used
whenever possible. Soil is a complex mixture of clay, silt+
sand, and organic material in various stages of decomposition.
By rotating crops, the fanner is able to improve soil structure,
break insect and disease cycles, and improve fertility.
legume such as alfalfa is an ideai crop for rotation.
With the advent of pesticides and herbicides in the USA,
many farmers grew maize year after year and found that,
although the pesticides controlled the insects and weeds, the
soil structure was slowly deteriorating.
The tern1 “land equivalent ratio” (LER) is used to compare
yields from different cropping systems. The LER reveals the
number of hectares in a monocultural system required to
produce the same amount produced by other cropping
systems. For example, a polycultural system that interplants
m&e with peanut is compared with the monocultures of both
= wt maize/ha in maize - peanut system
wt maize/ha in monoculture
wt peanut/ha in a maize - Deanut svstem
wt peanut/ha in monoculture
The crop yield in weight per hectare (wt/ha) is usually
used as rhe basis of comparison, but in calculating the LER, the
basis of comparison can be energy, total digestible nutrients,
dry matter, protein, or sales value.
3.5 cropping
3.6 Soiltilthand
3.1. Cropping calendar for
Northern Region, Ghana.8
Land preparation
“For’everything there is a season, and a time for every
matter, a time to be born, and a time to die; a time to plant,
and a time to pluck up what is planted;...“:
Typical cropping calendars for Africa, Asia, and North
America specify the time to perform particular operations for
various crops (Fig. 3.1,3.2). Since agriculture depends on the
seasons, timeliness is very important for good crop yield.
The condition-tilth-of
the soil is of paramount importance
to the farmer. Soil consists of solid particles separated by
voids that are partially or fully filled with water. The solid
particles range in diameter from sand (0.02-2.0 m:;: J to silt
(0.002-0.02 mm> to clay (< O.W2 mm ?.
Soil moisture is at field capacity when the SCJ!!Las reached
equilibrium in drainage, in other words, when gravity has
Basic fertilizer
and planting
3.2. Cropping calendar for
an irriaat& rice scheme in
Malaysia producing 2 rice
g$&$ presaturatbn ati Ia& soaking
%3% Plant
Land pieparation
drained water from the large pores, but the small pores remain
filled, since the capillary force holding the water is greater
than the gravitational force attempting to drain it away. In an
ideal soil for upland crops, about 50% of the volume is
occupied by solids, 25% by air, and 250/oby water.
Sandy and sandy-loam soils are coarse. More than half the
volume is occupied by solids. The coarse texture provides a
greater volume of large pores, so at field capacity over 25% of
the soil volume is air and less than 25?6 is water. Because of
the low water-holding capacity, sandy soils are >,aid to be
Clay and clay-loam soils are fine textured; less than half
the volume is occupied by solids. The fine texture provides
many small pores, so at field capaciy, Iess than 25% of the
volume is air and more than 25% is water. Because of the
amount of water in the soil, clay soils warm up later i,n the
spring, but are able to withstand droughty periods better than
other soils.
Soil is waterlogged when its moisture content is greater
than field capacity. A soil’s wilting point is reached when the
plant roots lose most of the water from the capilbnries. Ideally,
rainfall or irrigation keeps the soil moisture between the two
Tensiometers are instruments that provide readings on
soil moisture. A tensiometer usually consists of a vertical
piece of small-diameter tubing with a porous ceramic cup at
the bottom and a vacuum gauge at the top. The tube is filled
with water, and the bottom is placed in the root zone (or at
the soil depth at which information is required about soil
moisture). ,4 tensiometea ceases to function when air enters
it. In sandy soil, a tensiometer performs well over moisture
levels representing about 90% of the availabie water, while in
clay soil it records levels to about 50% of available water.
The weight of a cubic meter of dry sandy soil is greater
than that of a cubic meter of dry clay soil, yet farmers refer to
sandy soil as “light” and to clay soil as “heavy.” This is because
fine-textured soil such as clay is more difficult to work and
requires greater energy to cultivate than does a coarsetextured soil such as sand. Farmers usually prefer soil that
combines sand, silt, and clay, such as sandy loam or silty loam.
Because of variations in soil, climate, moisture, and crop,
tillage must be tailored to the situation to assure optimal soil
tilth and long-term crop production. Experiments in light and
heavy soils under semiarid rainfed conditions in Botswana
and Sudan provide information concerning tillage requirements in relation to soil type. The Botswana soil was a
ferruginous sandy loam classified as Luvisols/cambisoIs. Its
water-holding capacity was Iow, and,because of soil structure,
heavy rainfall, and intense sunlight. crusting of the soil surface
was common.10 Crusting inhibits water infiltration and
contributes to runoff and erosion. In contrast, the Sudan soil
was a black cotton montmoriltonitic c1a.ysoil classified as a
Vertisol. This soil is sticky when wet and cloddy wher! dry.
During the dry season, the soil shrinks, and deep cr;&s into
which a hand can be inserted appear. Dust and soil particles
fall into the cracks. When rain falls, water and surface material
are washed into the cracks, the montmorillonitic ciay
expands, and the material in the cracks mixes with deeper
A moldboard plow, a chisel plow, a one-way disc harrow,
and a shallow sweep were all used in the titlage experiments.
The crop was sorghum. In the Luvisols of semiarid Botswana,
the roots were confined to the depth of tillage, and the yield
was directly correlated with the depth of primary tillage. Soil
tilled with the moldboard plow lost the most moisture, and
planting depended on subsequent rainfall. Both moldboard
and chisel plows increased soil porosity to acceptable levels,
but the porosity was reduced by the compaction that
occurred while preparing the seedbed during secondary
tillage. A chisel plow or a one-way disc harrow was necessary
to loosen the root zone in compacted sandy Luvisols.
In the black cotton clay Vertisols in Sudan, the root system
was not confined to the depth of primary tillage, and there
were no significant differences between the yields of sorghum
or cotton at the various tillage depths. only shallow cultivation with a one-way disc harrow or application of a herbicide
to suppress weeds before planting was necessary. This is
fortunate, since plowing black cotton clay requires much
power and produces many clods, which must be pulverized
to form a seedbed.
Because the roots of upland crops require oxygen from
the soil, approximately 20% of soil volume must be air space.
Plant growth is retarded if soil air space is reduced to below
In wetland rice production, conditions are quite different.
No oxygen is required in the root zone; because the plant has
the ability to ingest oxygen through the leaves and transport
it to the roots. Rice is grown in standing water as a method
of weed control and to reduce the power required for manual
and animal tillage. Also, the crop does not suffer from lack
of water. Thus a ricefield does not require soil porosity. On
the contrary, soil particles are made fine by puddling so that
water will not percolate down through the bottom of the field
and be wasted.
Since the size of the pores and capillaries between the
solid particles of soil determines its water-holding and root
penetration characteristics, soil compaction by animals or
machines alters the soil’s physical characteristics. Internal
forces such as freezing, drying, and swelling, and external
forces such as rain, animals, vehicles, and tillage tools alter the
number and size of the pores.
The hooves of horses and cattle exert a pressure of
approximately 48 psi (331 kPa) on the soil; humans, 28 psi
(193 kPa); sheep, 18 psi (124 kPa); and farm tractors, about
10 psi (69 k?a). Although it appears that humans and animals
are a greater cause of soil compaction than farm tractors are,
the depth of soil compaction depends on the total weight of
the animal or vehicle as well as on the soil moisture. The
degree of soil compaction can be visualized as isopressure
lines plotted as pressure bulbs, as in Figure 3.3.
Tire size
Load, kg (lb) 300 (660)
3.3. lsopressure lines under
500 (1100)
11 x28
750 (1650)
1000 (2200)
Figure 3.3 illustrates a study12of how heavy wheel loads
increase the depth of compaction even though the tire
pressure remains constant and the soil is at normal desirable
field moisture and density The tire dimensions were chosen
according to the load SO that the soil contact areas were
proportional to the wheel load; thus, with all tires at an equal
tire mflation pressure of 0.84 atmosphere (85.1 kPa, 12.3 psig),
pressure distributions at the tire-soil contact areas were
assumed to be similar. In a hard dry soil, the 0.1 kg/cr+
isopressure line under the 11 x 2X tire would be about 13 cm
shallower, while for a wet soil it would be about 10 cm deeper
than in the normal soil shown in Figure 3.3.
Soil compaction can be useful or deuimental, but it is
usually the latter. In general, compacung the soil reduces the
number of larger pores and increases t,he number of smaller
pores, with the result that the soil loses drainage capacity and
nmains wet for a longer period after rains. A wet soil is
usually a cold soil. Because of the high specific heat of water,
more heat is required to warm wet soil than dry soil. In the
temperate zone, this phenomenon can be noted in the spring,
when the soil is wanned by bright sun and longer days. Seed
germination and 1Jant growth are delayed in wet soils.
Common methods for improving wet soils for upland
crops are installing subsurfa,ce tile drainage, growing crops on
mounds or ridges, staying off the soil when it is wet, replacing
wheel tractors with tracklayers, and crop rotations that
improve soil drainage.
The effect of soil compaction on soil moisture and crop
yield was demonstrated at MacDonald College in Ontario,
Canada, in 1976 and 1977. The experiments were conducted
on clay soil prepared by fall plowing followed by spring
rototilling to a depth of about 25 cm. The soil was then
compacted using 3 tractors with weights of 1700, 3515, and
4420 kg (3750, 7750, and 9750 lb) making O-15 passes either
before or after the planting of silage maize.‘)
The year 1976 was wet, with 16-20 cm more rain than
normal during the main growing season in Jtme and July. The
harvest re:‘e&d th::t the least dense soil (no tractor traffic)
gave the best yield, while the densest soil (15 tractor passes)
had about half the yield. In contrast, 1977 was dry, with 8-10
cm less rain than normal during the main growing season.
This time, the plots with a moderate amount of compaction
produced the best yield. In 1976 the problem was drainage,
not water storage, so large pores were an advantage. In I977
the problem was water storage, so small pores-created by
compressing large pores-were an ad~ntage.‘”
Slippage of a tractor’s drive tires is an important cause of
compaction. A tractor tire running in a furrow and slipping
due to the load it is pulling smears the soil surface and
squeezes out the voids below the bottom of the furrow. Plows
and disks working in wet soils with a high percentage of clay
also smear the soil at the bottom of their working depth. The
result is a thin, impervious layer called a plow sole. Soil
compaction is greatest when tractor drive wheel slippage is
between 15 and 25%. Above 25% slip, the tires throw soil off
to the sides, causing deep ruts.
The technique of tramlining or controlled tmffic farming
reduces soil compaction in the plant row, while increasing it
where the tractor wheels run between the rows. The first trip
of the tractor across the field produces 70-90% of the total
compaction. In a small grain crop such as wheat,, grain is not
planted in the rows where the tractors run. The wheels run
in the open rows so that the root zone is not compacted. Ridge
planting can also be used to control compaction. By keeping
the ridges in the same locations over a period of years, the soil
under cultivation is never compacted.
Cable systems wherein the implements are pulled across
the field by cables attach& tr? a winch are occasionally used
in research because they reduce compaction normally caused
by tractors.
A large 15-t wheel tractor may minimize soil compxtion
because it makes fewer trips across a field than a smaller
ii-actor. If the large tractor is used when the soil is too wet,
however, deep compaction wili result and adversely affect
crop yields for years. This IS unfortunate, because‘s large
tractor pulling a tillage too! made for a smaller tractor czn
operate in a wet field when soil conditions would prevent ihe
use of the same Qllage tool behind a sma!l tractor. Much of
the soil damage attributed to large tractors is due to tilling
when the soil is too wet.
The best tillage system cannot be determined by any hard
and fast rule. Wide variations in soils, temperature, rainfall
patterns, and crops demand that tillage be modified to fit
specific conditions. Frt?quently, the type of soil manipulation
must be varied from field to field on the same farm.
1. Food and Agricultrlre Orgylrnization (1974) Shifting cultivation and soii
conservation in Africa. Soils Bulletin 24. Paper presented ai the FAOt%XhV
ARCN Seminar, Jul 1973, Ibadan, Nigeria.
2. Ibid.
3. Erickson C I, (1985) Applications of prehistoric Ar~ctean technology:
,experiments in raised field agriculture, Huatta, lake Titicaca: I’)Hl-82. Pages
209-212 in Prehistoric intensive agriculture in the tropics. BAR international
Series 232. IS Farrington, ed. Oxford, England.
4. Kass D L (1978:) Polyculture cropping systems: review. and analysis.
Cornell International Agricultural Bulletin 32. Ithaca, New York.
5. Ibid., p. 55.
6. Pingali P, Bigot
Y, Binswanger H P (1987) Agricultural mechanization and
the evolution of farming systems in sub-Saharan Africa. The Johns Hopkins
University Press, Ddltimore.
7. Holy Bible (1952) Ecclesiastes, Chapter 3; Old Testament. Revised
standard version. Thorn&s Nelson Sr Sons Publishers. i%w York.
8. Ghanian-German Agriculturai Development Project - Northern and
Upper Regions (1977) Agricultural extension handbook, 1977. Tamale,
the ridges in the same locations over a period of years, the soil
under cultivation is never compacted.
Cable systems wherein the implements are pulled across
the field by cables attached to a winch are occasionally used
in research because they reduce compaction normally caused
by tractors.
A large 15-t wheel tractor may minimize soil compaction
because it makes fewer trips across a field than a smaller
&actor. If the large tractor is used when the soil is too wet,
however, deep compaction will result and adversely affect
crop yields for years. This is unfortunate, because’s large
tractor pulling a tillage tool made for a smaller tractor can
operate in a wet field when. soil conditions would prevent the
u;;e of the Same tillage tool behind a small tractor. Much of
the soil damage attributed to large tractors is due to tilling
when the soil is too wet.
The best tillage system cannot be determined by any hard
and fast rule. Wide variations in soils, temperature, rainfall
patterns, and crops demand that Gllage be modified to fit
specific conditions. Frequently, the type of soil manipulation
must be varied from field to field on the same farm.
1. Food and Agriculture Organization (1974) Shifting cultivation and soil
conservation in Africa. Soils Bulletin 24. Paper presented at the FAO/SIDA/
ARCN Seminar, Jul 1973, Ibadan, Nigeria.
2. Ibid.
3. Erickson C L (1985) Applications of prehistoric Andean technology:
experiments in rdised field agriculturel Huatta, Lake Titicaca: 1981-82. Pages
.209-212 irz Prehistoric intensive agriculture in the tropics. BAR International
Series 232. IS Farrington, ed. Oxford, England.
4. %dSSD L (1978) Polyculture cropping systems: review. and analysis.
Cornell International Agricultural Bulletin 32. Ithaca, New York.
5. Ibid., p. 55.
6. Pingali P, Bigot Y, Binswanger H P (1987~)Agricultural mechanization and
the evolution of farming systems in sub-Sahardn Africa. Thejohns Hopkins
University Press, Haltimore.
7. Holy Bible (1952) &XkSidSteS.Chapter 3; Old TeStaIImlt. Revised
standard version. Thom& Nelson & Sons Publishers, New York.
8. Ghanian-German Agricultural Development Project - Northern and
Upper Regions (1977) Agricultural extensiorl handbook, 1977. Tamale,
9. Thavardj S H (1978) The importance of integrating nonengineering
aspects in irrigation system design. Pages 15-24 it2 Irrigation policy and
managemel-i in Southeast Asia. International Rice hsedrch Institute, P.O.
Box 9% Manibd,Philippines.
IO. Willcocks T J (1984)Tiliage requirements in relation to soil type in semiarid rainfed agriculture. J. Agric. Eng. Res. 30:227-336.
11. Sohne W (1953) Druckverteilung im B&en Und Bodenverformung
Unter Schepperreifen (Distribution of pressure in soil and soil deformation
under tractor tires). Grundlagen Der Landtechnik, Heft 5. p. 51.
12. Ibid., p. 49-63.
13. Raghavan G S V, McKyes E, Gendron G, Borglum 13 K, Le H H (1978)
Effects of tire contact pressure on corn yield. Can. Agric. Eng. 20 (1):34-37.
14. McKyes E (1980) Fielcl traffic impact on soil compactic%
Agricultural Engineering Extension Bulletin 449. Proceedings c.. a seminar
on the influence of tillage practices on crop growth.
Dep;, rment of
Agricultural Engineering, Cornell University, Ithaca, New York.
Drache H M (1964) Tht! day of the bonanza. North Dakota Institute for
Regional Studies, Fargo,
Jurion F, HenryJ (1969) Can primitive farming be modernized? [translated
from French by Agra Europal. Wellens-pay, s.a.. Bruxelles, Belgium.
Publications de I’Institut National pour l'E!ucle Agronomique du Congo.
Kamarck A M (1976) The tropics and economic development.
Hopkins University Press, Baltimore.
The Johns
Kuipers H (1984) The challenge of soil cultivations and soil water problems.
J. Agric. Eng. Res. 29:177-l%.
Marling R W (1982) The pros and cons of controlled traffic farming. Paper
82- 1043. American Society of Agricultural Engineers, St. Joseph, Michigan.
Schafer ti L,Johnson C E, Elkins C B, HendrickJ G (195X) Prescription tillage:
the concept and c?xampies. J. [email protected] Eng. Res. 32:123-129.
Wijewarclene R (1978) Systems and energy in tropical farming. Paper 7%
~1511 Americar, Society of Agriculturdl Engineers, St. Joseph. Michigan.
Wijewarciene R (1981) Technic:ues and tools, conservation farming for small
Farmers in the hmTlic! tropics. International Instiiutc of Tropical Agriculture
Sri Lanka Program, Colombo.
Tillage is the manipulation of soil to obtain favorable conditions for plant growth. Good tillage provides a proper
seedbed. For example, a lettuce seed requires a seedbed
consisting of fine partic!es, since the seed itself is very small.
Weed control is also obtained through tillage by turning the
weeds under the soil with a moldboard plow before planting
a new crop. After depositing the weeds I 5 cm below the surface, the seeds of the newly planted crop can germinate and
grow without competition for sunlight, water, and nutrients.
The weeds will return, but by that time the crop will be large
enough to compete.
Organic matter from weeds, crop residues, or green
manure creates better soil tilth. Decomposing organic matter
also improves soil fertility.
Tillage is also used to provide the desired contour for
certain crops. For example, a specific type of plow called a
ridger is used to form ridges on which peanuts are planted.
In irrigated rice production, tillage practices keep the field
level and prevent the loss of water.
Tillage practices are determined by the type of soil, crop,
topography, and available power.
4.1 Tillage tool
Tillage tools may be classified according to
condition of seedbed
- primary
- secondary
disposition of surface debris
- inverted (trash buried)
- not inverted (trash on surface)
power source
- human-powered
- animal-drawn
- tractor-powered
Soilis not prepared for seeding or transplanting in a single
operation in most fdrming systems. Instead, a rough form of
tillage such as plowing is first accomplished. This operation
is called primary tillage. Secondary tillage refers to smoothing
the rough ,condition of the soil surface into a seedbed. The
primary and secondary tillage phases are combined when
using a powered rotary tiller because the action of the tines
can produce a finished seedbed in one pass.
Prim;,ry tillage tools that do not invert the soil are the hoe,
ard, chisel plow. and subsoiler.
Primary tillage tools that &invert the soil are the spade,
moldboard plow, disc plow, rotary tiller, and rotary spading
4.2 Hoes
4.1. Digging hoe.
The hoe used for primary tillage in many parts of the world
is quite different from the long-handled, lightweight hoe
familiar to the North American or European gardener. The
digging hoe shown in Figure 4.1 weighs about 4 kg. It has a
short, stout, wooden handle about 1 m in length and a steel
blade approximately 10 cm wide by 30 cm long. The angle
between the handle and the blade is approximately 60”.
Hoes differ according to the size of the blade, the angle
between the handle and blade, and the method of att3ching
the handle to the blade. Some primitive blades are made from
wood, but today this is uncommon since scrap metal 01
manufactured blades are available in most parts of the world.
The best blades are made of forged and heat-treated steel, and
have a D-shaped eye through which the wooden handle is
securely wedged.
Some hoe blades are affixed to the digging hoe handle by
a spike welded to the top of the blade. The blades of primitive
hoes are lashed to the handle with cord. These two types of
blades are satisfactory for light work such as weeding, but not
for primary cultivation.
Digging hoes have shc,rt handles because they are used
for heavy work and demand the expenditure of considerable
force. If the handle were longer so the fa~rmerneed not stoop,
it would have to be much stouter (and heavier) to avoid
breakage. The digging hoe is the product of many generations
of development, and usually reflects the best design possible
under the constraints of available materials, manufacturing
facilities, farming practices, cost, and power of the user. It is
extremely difficult for an engineer to improve a locally made
hoe without increasing the cost to a greater degree than the
improvement. One example of hoe improvement is where
West African blacksmiths changed from mild (low carbon)
steel scrap to leaf springs from wrecked trucks. Truck springs
are made from high carban steel, which can be heat-treated
to obtain a durable cutting edge and greater strength.
Hoes show great variance in width and in the angle
between the blade and the h&ndle.’ For example, a hoe for
use in a ricefield has a w&i- blade than one used on hard, dy
upland soil. The angIL’ between handle and blade in the hoe
used tc: ‘:-~.!iGri, 4ield banks (bunds> diffe1.s from that in the
hoe UYCC~ it,i ti!litlg tt-li E”c;J.
Reparing dry soil Taoa depth of 10-15 cm witl, a &&gin;;
hoe requires approximately 300 nk:+hours per hectare (manh/ha), while 100-200 man-h/ha are required to complete
primary tillage in flooded soil.’
4.3 Spades and
Spades and shovels are used to dig, lift, and invert soil to
prepare a seedbed. They are also used to dig postholes and
ditches. Although spades and shovels are commonly used in
North America for tilling home vegetable gardens, they are not
used for land preparation in LDCs. Since the common spade
or shovel requires foot pressure when spading earth, the user
must wear a pair of stout shves, unless the tool is constructed
with a broad footrest to make it usable w~ith bare feet.
The blade of a spade has little curvature and is rectangular
in shape. The handle is about 70 cm long, and the grip is either
D- or T-shaped. The D-shapecl~top with a pressed steel
retainer holding a hardwood grip is the most sarisfactory for
strength and comfort (Fig. 4.2).
The long-handled shovel (Fig. 4.3) is about 150 cm Ilong.
It has a pointed, curved blade approximately 22 cm wide at
the head and 30 cm long. The handle’s diameter tapers from
4 cm at the blade to 3 cm at the end. Such a shovel weighs
approxi,mately 2 kg.
4.2. Spade with a D-shaped
hand grip.
4.3. Poin!ed shovel.
4.4. Foot plow (chaquitaqlla)
(far right).
4.5. Chaquitaqlla blades.
The foot plow or chaquitaqlla, also called a rhuki or shuki, is
indigenous to the Andean region, where it was developed
1300 to 2500 yr ago.3 It is still used in Peru, Bolivia, and the
mountainous regions of neighboring Andean countries.
Steep slopes are farmed in the Andes using a fallow system of
agriculture. The foot plow, shown in Figure 4.4, is a tool aade
from local materials; it is designed to enable farmers to invert
sod at the end of the fallow period and to do other tasks as
well. The foot plow is used more like a pry bar than a shovel.
The <Zrstchaquitaqlkr was probably a pointed pole with an
attached footrest. Today, a typical foot plow is 1.45 m long,
with a pole diameter of 7 cm and a blade 13 cm wide. The
foot plow consists of four parts: wooden pole, handhold,
footrest, and metal blade. The wooden handhold is fastened
to the pole with the rope that supports the footrest. Sometimes
the handhold is a projection from the pole, which is often
fashioned from a natural branch on the tree from which the
pole is cut. The footrest is a wooden step attached to the pole
by leather thongs. A braided rope, usually of llama hair,
secures the footrest to the handhold. The rope prevents the
footrest from slipping on the pole and provides adjustment to
suit the farmer. The steel blade (Fig. 4.5) fastened to the
bottom end of the pole is usually fabricated from automobile
or truck leaf spring. The cutting edge of the blade varies
according to the soil. In stony soils, the blade is narrow and
pointed; in stone-free soils, the blade flairs like an ax head.
A typical use of the foot plow is to prepare the soil for
planting potato on steep slopes at 3.000-4,000 m altitude.
Potatoes are planted in rows that either run vertically down
Stone-free eSOil
4.6. Potato seedbed
prepared by a chaquitaqlla.
Potato danted here
the slope or are arranged in a herringbone pattern. Working
with a foot plow on a steep slope is easier if one begins at the
top and works downward. Generally, several farmers work
toget.her. Potatoes are planted in the slots created by abutting
pieces of sod, as depicted in Figure 4.6.
4.5 Ads
4.7. Body ard (India).
Ards, chisel plows, field cultivators, and subsoilers belong to
a group of tillage implernents that do not invert the soil. Most
of the crop residue and clods remain exposed on the surface
of fields tilled with ards.
The ard is a single-point chisel plow and is sometimes
called a breaking plow. Sumerians used ards around 3600 BC.
Animal-drawn ards are still used today in n~any areas of the
world. The ard is used primarily for shallow tillage in semiarid
areas. Since the ard does not invert the soil and leaves a layer
of trash on the surface, it helps to alleviate the effects of wind
Ards can be categorized into two major groups (body ards
.and beam ards) and three minor groups (sole ards, triangular
arcls, and quadrangular ards>.’ Figures 4.7-4.10 illustrate four
common ards in use today.
In the body ard, the body (which is composed of a soil
engaging point and a handle) is pierced by the beam. In the
4.6. Beam ard (Ethiopia).
4.9. Sole ard (Peru).
4.10. Quadrangular ard
beam ard, the beam is pierced by the body. The sole ard
features a horizontal sole and point to which the beam and the
handle are attached. It probably evolvecl from the body ard.
Various modifications of the basic beam and body ards
evolved to improve plow strength or better fit local agricultural conditions. Triangular ards were developed in some
countries to provide stronger, more rigid implements. The
quadrangular ard has a horizontal sole with the beam parallel
to the ground and the handle nearly perpendicuku.
Ards are generally made of wood, except for a steel share
point. To steer an ard, the handle is moved opposite to the
desired direction of travel. Depth adjustment is made by
changing the angle between the beam and the body. This is
accomplished by hitching the beam closer to or further away
from the yoke, by extending or retracting the share tip in
relation to the point, or by altering the position of a wedge or
A typical ard weighs about 15 kg. Examination of ards and
ox yokes in Ethj~opiarevealed that an ard and shoulder yoke
for 2 oxen had a total weight of 20 kg, which is light enough
for the farmer to carry both implements to the field.
Experiments were conducted in northernjutland in 196268 with a replica of a beam ard of 350 BC. Two Jersey oxen
were utilized as draft animals. Tests were carried out on 18mo-old grassland on sandy soil, The grass was cut and
removed before plowing. With the share tip IO cm ahead of
the ard head, plowing depth was 12.6 cm. When the share tip
was 20 cm ahead of the point of the ard head, plowing depth
was increased to 15.4 cm. The 15.4 cm depth did, not, resu!t
in broader furrows or better soil nreparation. Furrow width
was approximately 10 cm. Speed of plowing was 4 km/h with
an average draft of 100 kgf (0.98 kN, 220 lb) and peaks of 150
kgf (1.5 kN, 330 lb). Drawbar horsepower was 1.5.”
One plowing with an ard is usually insufficient to prepare
a seedbed. From two to six passes may be required,
depending upon the vegetation in the field at the time of
piowing and the type of seed to be sown. Heavy sod in a field
that has been fallow for a number of years or land preparation
for a seedbed for small seeds will necessitate perhaps four or
five trips across the field; a field with a friable soil and a light
stubble such as bean stubble, or land preparation for large
seeds such as maize or beans will require only two or three
trips across the field. When preparing a field, each successive
plowing is done at an angle to the previous t,rips across the
field. For example, the second plowing may be done :at40”,
the third at 150’, and the fourth at 90” to the first.
Through time the body arc1developed into the moldboard
4.6 Chisel plows
The tractor-drawn chisel plow (Fig. 4.11) is a primary tillage
implement with a working depth of IO-30 cm. It is a modern
version of the ard. Since the chisel plow, unlike the
moldboard plow, does not expend energy inverting the soil,
4.11. Chisel plow.
it requires less energy per unit of width tiiled. Furthermore,
the back furrows and dead furrows associated, with mokihoard plows are eliminated.
A chisel plow consists of a number of shanks attachecl to
laWal tool bars! which form the frame. The vertical clearance
fr<;m the frame tu the chisel point varies from 55 to 80 cm.
Sufficient distance between fraine analsoil is essential fbr tr:rsh
Mounted chisel piows are av&ble in widths
ranging from 1.5 to 6 m wide. Trailing chisel plows are 2.5
to 14 m wide.
Chisel plows are usually either two- or three-l:yar units.
Since normal shank spacing is 1 shank per 30 cm Cl ftj of
wicltht a 24,ar frdme must, have a shank every 60 cm, while t,he
shanks on :I j-bar frame are spaced every !)Ocm. The threebar unit thus provides more space for trash movement. The
typical chisel plow shank is a curved piece of spring steel with
3 cross section of 2.5 x 5 cm for ;I regular shank and 3 x 5 cm
for a heavy-duty shank. Shanks are identified by cross section
and clearance. Typical shank clearances are 20, 25, and 30 in
(55, 65, anci 80 cm). The shank is secureci to the frame by a
rigid mounting for use in rock-free soil. In rocky soil, shanks
are mounted to the frame by the more expensive spring cushioned clamps.
Shovels, sweeps, or spikes are mounted on the shanks.
Reversible shovels 5 cm -wide are the most common. Power
requirements are less for shovels than fi,r sweel,s or twistetl
shovels. A twisted shovel is used to turn earth ancl trash aside,
mix more of the trash into the soil, and leave a rougher soil
surface. Both right-hand and left-hand twisted shovels are
Sweeps are used primarily for weed control. Working
depth is usually shallow-approximately
10 cm. Depth is
controlled by gauge wheels.
In the semiarid regions of the U.S.?where a summer fallow
is customary, a chisel plow or field cultivator equipped with
wide sweeps is often referred to as a duckfoot cultivator.
The main frame of a chisel plow should be parallel to the
ground so all teeth work at the same depth. Working speed
is 7-10 km/h. Higher speeds help to alleviate plugging in
heavy trash conditions. If proper ground speed c.mnot be
maintained while working at the desired depth, two passes
are made. The first pass is shallow. The second pass is at an
angle to the first pass and at the desired depth.
The horsepower values in Tdble 4.1 are approximate for
chisel plows equipped with 5-cm-wide (2 in) shovels. The
table assumes that the tractor’s maximum Jrawbar horsepower is 75% of the maximum P’I’O horsepower. Power
requirements vary when using twisted shovels or sweeps.
In general, a chisel plow requires l/3 to l/2 the power
required by a moldboard plow for the same depth, width of
tillage, and speed. The moldboard uses more power because
it inverts all of the soil, while the chisel does not disturb all the
soil, nor does it invert the soil. Chisel plows have become
popular in continuous maize production syst.emsusing herbicides. Before herbicides were available, the moldboard plow
was often required to bury weeds so as t.2 give seedlings a
headstart. With the advent of herbicides, hoii.ever, the chisel
plow’s lower power requi.rement made it more practical.
Table 4.1. Tractor requirements for a chisel plow (tractor
Depth in
cm (in)
Speed in
km/h (mph)
15 (45)
8 (5)
8 (5)
8 (5)
8 (5)
20 (6)
25 (10)
30 (12)
PTO hpl
PTO hp/shank
Sandy loam
4.7 Field cultivators
A field cultivator is difficult, to distinguish from a chisel plow.
Essentially, it is a lightweight chisel plow with closer shank
spacing and less vertical clearance. It is a secondary tillage
tool. Mounted field cultivators range from 2.4 to 7.3 m (8 to
24 ft) in width, while trailing models range from 2.4 to 18 m
(8 to 60 ft). They are manufacrured in both two-bar and threebar frames. As with the chisel plow, three-bar frames provide
more clearance than two-bar frames. Field cultivator shanks
are mounted to provide lS- to 25cm (6 to 10” in) spacing.
Shanks may be either rigidly mounted or spring mounted.
Sweeps, shovels, and points are similar to those on chisel
plows. The usual working depth for a field cultivator is 8-I 3
cm. Power requirements are given in Table 4.2.
4.8 subsoilers
A subsoiler is a chisel plow designed to work at a depth of 50
cm (‘18 in>. Common subsoilers have maximum plowing
depths of 40-60 cm (15 to 24 in). Plowing at that depth
requires a very rugged chisel and considerable power. The
main reason for using a su!>soiler is to break the hardpttn for
better moisture control. In some dly soils. it is possible to
crack the earth to a depth of 60 cm on each side of the point
of the subsoiler chisel.
Subsoilers are usually tr;icto:--n10Llnted units with one to
nine chisels. Some units can lx attached at adjustable spacing
on two bars, A popular 9-shank unityhas %-cm (21-in) spacing
between shanks. Some subsoilers with multiple shanks have
automatic trip mechanisms. Each shank is free to trip
independently of the others whenever an obstruction is
encountered. As soon as the obstruction is passed. the shank
:mtomatically returns to working depth. On mult.iple shank
subsoilers, gauge wheels are used to maintain depth of
Moles and pipe and cable laying attachments are available
for many units. Sutxoilers are not Ixxxficial under at1 soil
Table 4.2. Tractor requirements for a field cultivator (tractor PTO hp/
PTO hp/shank
Depth in
cm (in)
Speed in
km/h (mph)
Sandy loam
13 (5)
8 (5)
conditions. For example, when water under pressure underlays an impermeable layer of subsoil, subsoiling can fracture
the layer and result in a wet field. Dry, clayey soils receive
more benefit from subsoiling than do wet or sandy soils. The
subsoiler’s power requirements are given in Table 4.3.
Subsoilers are usually classified by the type of shank. The
vertical, parabolic, and 45” leg are the most common (Fig.
The Howard Paraplow’rhqis a 45” leg subsoiler that has an
adjustable shatter plate so that the degree of fracture can be
adjusted to soil and power conditions. A vertical tine moving
through the soil creates fracture lines radii&g out at 45”
angles from the tine. The Prtr~plcw~~ utilizes this soil
characteristic by situating the pl:>;~~point and the landside at
the bottom end of the shin. An adjustable, rudder-like shatter
plate, which comprises the leading and trailing edges of the
45” portion of the leg, is also fitted to the shin. The cross
section of the shin, leg, and shatter rlate assembly rese:nbles
an airfoil. As the soil flows over the upper surface of the fS1,
it is subjected to tension and cracks. rr ,Y :;oil is too plastic
to fracture, the shatter plate can be adjusted to force the So)i:
to greater tensile stress so that it will fracture. Producing
greater stress requires increased energy, and thus increased
tractor horsepower.
The Parapic)‘Lv’”is a right-hand machine like a moldboard
plow and should be worked at a speed of 3-5 mph (5-H km/
h). It cannot be worked from one side of a field to the other
like the other types of subsoilers or chisel plows and field
The tractor wheels must be set so that the tires do not run
over the finished work and compact the loosened soil. For the
maximum working depth, the legs are set on 20-in (50-cm’)
Table 4.3. Tractor requirements
Depth in
cm (in)
30 (12)
45 (18)
60 (24)
for a subsoiler
(tractor PTO hpl
PTO hp/shank
Speed in
km/h (mph)
6.5 (4)
6.5 (4)
6.5 (4)
4.12. Types of subsoilers.
Paraplow 45” leg
When beginning work in a field, the shatter plate should
be set for the least protrusion above the leg. If soil fracturing
is not satisfactory, the angle of the shatter plate to the leg
should be increased until it is. The Paraplow7” is designed to
work at a maximum d,eptl! of 14 in (36 cm).
4.9 Moldbard
The primary advantage of the moldboard plow is that it does
an excellent job of inverting the soil and burying surface trash.
The moldboard plow can be visualized as two wedges. The
share, landside, a.nd moldboard form the wedges. A moldboard plow viewed from the side resembles a wedge formed
by the share and the moldboard. This wedge cuts and lifts the
furrow slice. Viewed from the top, the plow looks like a
wedge formed by the landside. share, and moldboard, This
wedge moves t!ie furrow slice to the side while simultaneously inverting it
Figure 4.13 shows the parts of a plow bottom. Moldboard
plows are mdde largely of mild steel. The share, however, is
usually made from a special alloy or laminated steel. The
moldboard is fabricated from an alloy steel with good
scouring properties. Cast iron is satisfactory for shares and
moldboards if the plow is used in conditions free of stones or
other obstructions; however, few tractor plows are made of it
Occasionally, ntoldboards are made of fiberglass.
Moldboard plows. when properly adjusted, automatically
seek the designated depth. It is unnecessary to add weight to
a moldboard plow to penetrate the soil to the desired depth.
The plowshare is designed to provide down suction and
side suction. Down suction causes the plow bottom to
4.13. Moldboard plow
Landside heel
Gunnel of share
Point df share
penetra:e the soil, while side suction holds the plow .to an
even full-width furrow. Too much down suction makes it
difficult to control plowing depth, while too little d,own
suction causes the plow to run too shallow. Too little down
suction is more common than too much. Too little side
suction allows the plow to weave, making it difficult to plow
a straight furrow. Too much side suction makes the plow
bottom take too wide a cut, resulting in a poor job of plowing.
Down suction is regulated by altering the distance that the
bottom of the share and landside deviate from a straight line.
Side su~ctionis adjusted in the same general manner. The
nominal clearance required for both down suction and side
suction is 0.7 cm (0.3 in). As the share wears, the offset
required for proper suction decreases, and insufficient suction
results. Proper suction can be restored by sharpening or
replacing the share. Figures 4.14 and 4.15 illustrate the offsets
for doT,\rnand side suction.
4.14. Offset for down suction.
4.15. Offset for side suction.
The water buffalo-drawn single moldboard plows use4 to
plow ricefields perform well in the plastic soil of a ricefield,
but they are unsatisfactory on upland soil, since the point and
the share are not shaped to obtain sufficient suction to
penetrate and operate at the desired depth in dry soil.
Moldboard plows are usually right-hand plows. When
one stands behind the plow facing the directioit of travel, the
landside is to the left and the moldboard to the right, so that
the furrow slice is thrown to the right: A left-handed plow has
the moldboard on the left and the landside on the right, and
throws the furrow slice to the left.
Some single-bottom walking plows designed for draft
animals allow for the moldboard and share to operate either
right- or left-handed. In North America, this type of walking
plow is referred to as a hillside plow, since the reversible
feature allows all the furrow slices to be thrown up the hill
When plowing irrigated or contoured land, it is often
advantageous to be able to use a right-hand plow in one
direction and a left-hand plow in the opposite. To accomplish
this, a left-hand and a right-hand plow are mounted on a
common frame. This unit is called a two-way or a reversible
The size of a moldboard plow is determined by the width
of the plow bottom and the number of bottoms. For example,
a 3-14 is a 3-bottom plow with each bottom cutting a 1Cinch
(36cm.> furrow.
The width of a moldboard plow is the perpendicular
distance from the soil-contacting side of the landside to the
wing of the share. A moldboard plow is generally designed
to plow at a depth equal to half the bottom’s width of cut. For
example, a 14-in (36cm> plow will easily plow ‘7 in (18 cm>
deep. Multi-bottomed tractor plows of variable width complicate the matter of plow size. A typical 7-bottom variable width
unit can plow at bottom widths of 35-56 cm (14-22 in>. The
plow bottoms are attached to the frame so that by hydraulically adjusting the angle of the plow beam, the furrow cut can
be changed to the desired width between a minimum of 2.5
m (8.2 ft) and a maximum of 3.9 m (12.8 ft).
A plow can also be categorized according to its prime
mover. An animal-drawn plow controlled by a man on foot
is called a walking plow. If the plow is mounted on wheels
and the plowman rides, the unit is called a sulky plow.
Tractor-drawn plows are categorized by the method of
attachment to the tractor: trailing, mounted, or semimounted.
The trailing type plow is essentially a sulky plow pulled
by a tractor. Today. trailing plows are rarely used with
tractors, since the hydraulic systems and weight transfer
arrangements on modern tractors are far more convenient.
The mounted plow is fully mounted on the tractor and is
lifted from and dropped into the soil by the tractor’s hydraulic
system. A mounted plow is less expensive than a trailing or
semimounted plow, since it requires less framework. When
it is lifted for transport1 however. the entire weight of the plow
overhangs the rear of the tractor, so mounted plows are
limited to about four bottoms in the interest of s:ability and
safety. If the tractor has both front and rear three-point
hitches, mounted plows can be hitched both front and back.
A typical arrangement is a four-bottom mounted plow on the
rear and a three-bottom unit on the front.
Semimounted plows are the most pc-p&r type of moldboard plow arrangement in North America. The semimounted
plow is a compromise between the trailing plow and the full
or integral mounted plow. Like the trailing plow, a rear furrow
wheel carries some of the weight. This wheel is usually
steerable on multi-bottomed plows to enable the tractor to
turn within a reasonable distance. Like the fully mounted
plow, the front is attached to the tractor’s three-point hitch and
raised and lowered hydraulically. The lift linkage on such a
plow is devised so that the bottoms do not enter or leave the
soil at the same instant. To make straight headlands, the front
bottom enters the soil while the rear bottom is still raised. The
rear bottom automatically enters the soil ;t the same distance
from the starting point as did the first bottljm.
Although the plow bottom is the heArt of a moldboard
plow, certain accessories are necessary for good $0~ ing
under various conditions. Coulters ar.d jointers, for example,
are used to cut the furrow slice loo.;e from the furrow wall,
thus preventing the shin from tearing it loose. By eliminating
the tearing action, plow draft is reduced. Coulters or jointers
are especially useful when plowing sod.
A knife coulter is a vertical steel knife bolted to the plow
beam so that the point of the knife is above the point of the
share. On some plows, the knife coulter is bolted to the
landside of the share and protrudes upward. This design is
called a fin coulter.
A rolling coulter is a hard steel disc with a sharp edge. It
is usually flat, but it often resembles a section of a sphere. Not
only does the rolling coulter cut a smooth furrow face, but it
cuts surface trash better than other coulters. Rolling coulters
are available in plain, notched, and ripple-edge discs. The
plain coulter is the least costly and performs satisfactorily
when there is little surface trash. The notched coulter will hold
clown and cut heavy trash, such as maize stalks, but is more
difficult to sharpen than the plain coulter. Ripple-edge
coulters cut like serrated knives. They are more positively
rotated by their engagement in the soil than the other rolling
coulters. Ripple-edge coulters are also self-sharpening,
Large-diameter rolling coulters are better for cutting trash
than smaller diameter coulters. which tend to push heavy
trash ahead instead of cutting through it. On the other hand,
large diameter coulters do not penetrate the soil as easily as
small ones. When plowing hard soil, the coulter is set at
shallow depth and rearward of its usual location so as not to
adversely affect the penetration of the plow. The diameter of
a rolling coulter should be equal to or larger than the size of
the plow bottom with which it is used.
For average plowing, the coulter is set slightiy ahead of the
share. It is adjusted to cut to half the plowing depth. The
coulter is installed about 2 cm (0.75 in) from the outside of the
A jointer is a miniature plow. Its purpose is to turn over
a small ribbon ‘of soil directly above the plow point, thus
helping the plow bottom to turn the furrow. A jointer is
mounted on the plow beam in the same manner as a knife
coulter. Where surface trash exists, jointers perform better
than knife coulters, but not as well as rolling coulters.
Shock protection devices prevent breakage of the share,
twisting of the plow standard, or warping of the beam or
frame. Various types of devices are utilized. Walking plows
usually have no shock absorbing features. Sulky plows utilize
a shear bolt or a spring-loaded latch to protect the plow when
it strikes an obstruction. Integral mounted tractor plows
cushion the shock of hitting an obstruction with either a
breakaway spring latch or a hydraulic system that releases the
Tractor-drawn plows of one to three bottoms generally
utilize a spring reset arrangement. When the bottom strikes
an obstruction, it is lifted out of the soil by t,he combination
of forward travel and spring action. The plowman must then
reverse the tractor and plow to reset the bottom. This system
is inefficient for large tractors and plows. For example, if one
bottom of a seven-bottom plow strikes an obstruction and
pivots out of the soil, it is necessay to back up the entire rig
to retrieve it, thus interrupting the work of the six other
Automatic trip beams actuated by springs, air pressure, or
hydraulics are used with most moldboard plows of four or
more bot,toms (Fig. 4.16). The hydraulic system is the most
common. With automatic trip beams, it is not necessary to
stop or even reduce speed when a bottom strikes an obstruction, since the bottom will disengage and reenter the soil after
passing over the obstruction.
4.16. Action of an automatic
trip beam when plow bottom
hits rock.
Ail moldboards lift, fracture, and invert the furrow slice,
but significant differences exist. Moldboard shapes are
designed according to soil characteristics, degree of covering
desired, speed, and draft restrictions. Of the hundreds of
moldboard shapes, the most important are the sod, stubble,
general purpose, high speed, and slatted.
The long, low sod moldboard is designed for turning
virgin sod or land that has been idle for a long time. It is
sometimes called a breaker bottom. The sod moldboard
provides a long, augerlike twist to the furrow slice so that the
slice is completely inverted.
The stubble moldboard is wide and has an abrupt curve
that causes the furrow slice to be thrown over quickly. It
pulverizes the soil better than other types of n~oldboards. This
moldboard performs best, on annually cukivated land.
The general purpose moldboard is a cross between the
sod and stubble designs. It provides the farmer with one
moldboard suitable for general farming.
The power of farm tractors has increased faster than their
draft capabilities; therefore, farmers are plowing at higher
speeds today than they were two or three decades ago. Since
drawbar horsepower = draft x speed x constant, if draft is
limited tIecause of wheel and soil conditions, the farmer
plows at a higher speed to utilize his available tractor power.
A stubble bottom that plows well at 4 km/h does not suffice
at high speed. The abrupt curvature of the stubble moldboard
throws the furrow :;lice too far, and may even roll the slice 360”
and leave it uninverted. The high-speed bottom has a longer
moldboard with less curvature,. and turns the furrow evenly
when drawn at high speed,s.
4.17. Horizontal adjustment
of walking plow.
Slatted moldboards are used in soils that do not scour well.
Longitudinal sections of the moldboards are removed, leaving
only about half the moldboard surface intact. The remaining
moldboard surface produces higher soil pressure, thus preventing the soil from sticking to the moldboard.
Proper hitching of the plow to the draft animal or tractor
is equally important as selecting the correct plow. When
properly hitched, the plow’s load vectors are in equilibrium
&th the pulling vectors of the tractor or draft animal. The
center of resistance of a moldboarcl plow bottom is on the
surface, to the right of the shin (Ifor a right-hand bottom)
where the share butts against the moldboard. The line of pull
is an imaginary straight line with the center of resistance at one
end and the center of power at the other. To secure a good
hitch and to prevent sidewise pull and energy waste, the line
of pull must pass through the clevis, or hitch point. The
horizontal vector of the line of pull is the line of draft (Fig. 4.17,
4.18). The lirie of draft must pass through point R in Figure
4.17. If it passes through points A or C, the plow will pull
sidewise. In Figure 4.18, the line of draft runs from the harness
hames to point G at the plow’s center of resistance. Since the
line of pull passes through point E, the hitch poiht must be E.
If the hitch point is D1 the plow goes deeper into the soil. If
the hitch point is F, the plow is t,oo shallow. When the plow
is adjusted properly, the plowman does not need to fight it.
The only strenuous work occurs when turning at the end of
the field.
The importance of hitching also applies to multi-bottom
tractor plows. The center of resistance on a plow bottom is
about l/4 the width of cut. For an B-inch plow bottom, for
example, the center of resistance is 4 l/2 inches from the shin.
or 13 l/2 inches from the wing tip of the share. I3y ad,ding half
the width of cut for each additional bottom, the horizontal
center of resistance is determined. For example, a 5-18
plow’s center of resistance as measured from the right willsbe
13 l/2 + 9 + 9 + 9 + 9 = 49 l/2 in. To make the plow run straight,,
the line of draft between the center of resistance and the
center of power on the tractor must pass through the propel
hitch point (Fig. 4.19). Since the center of resistance is an
estimate, it is advisable to adjust the hitch point after observing
plowing perfLxmancc. If the plow cuts less than nominal
width, the hitch must be moved to point IS. If the plow cuts
4.16. Vertical adjustment of
walking plow.
4.19. Hitching a tractor plow.
greater than nominal width, it mist be hitched at point C. The
same procedure is applicable to the vertical hitching of tractof
plows. Vertical hitch l~djustments cm be made at the plow
hitch or tractor drawbar for trailing and sen~imounted plows.
When pulling up to five bottoms, the right-hand wheels of the
tractor travel in the furrow while the left-hand wheels arc on
the Iand (unplowed soil 1. For five or more bottoms. it is
possible to hitch so that all wheels of the tractor are on the
Plow draft and power required for rnolcllx~ard plo\x3
depend primarily on the type of soil plo~ved and the speed
with which it is plowed. Table 4.4 provides typical values for
a 4bottoni I&in (45cm) niolcllxmd plow plowing to a depth
of8 in (20 cm). For plows of other sizes, draft ancl IlorscpoweI
can be pK)rdtecl according to plowing width. depth. and
number of bottoms.
Table 4.4. Power required for P 4-16 moldbowd plow at &in (20~cm)
plow depth.
4.10 Disk plows
4.20. Semimounted disk
Power required (dwb hp)
Sandy loam
The disk plow (Fig. 4.20) is used for primary tillage to invert
the soil or to mix the surface vegetation. A disk plow requires
about loo/~more draft per area of soil turned than a moldboard
plow, but it is preferable to the moldboard plow when
the soil contains large roots or stone ledges;
the soil ,is sticky, and a moldboard cannot SCOUI‘;
the soil is dry and hard, and a moldboard plow does not
penetrate to the desired depth; or
tractor operators are not well trained.
A disk plow consists of a frame containing one to seven
concave steel disk blades and a tail wheel. The diameter of
the disk blades is 61-97 cm (24-38 in). The blades are made
from 5-6 mm steel and are shaped like sphere segments. They
are set so that the face of the blade is at about a 45” angle to
the direction of travel and tilted rearward 15-25” from the
vertical. Setting the disk blade farther from the vertical
improves penetration in heavy or sticky soils, while setting it
closer to the vertical improves performance in loose or brittle
soils, and provides better trash coverage.
Each disk blade makes a cut 18-30 cm (7-12 in) wide,
depending on disk diameter and setting. Unlike a moldboard
plow, a disk blade creates no suction. Weight must be added
to force the blades to penetrate deeper. Each blade carries a
weight of 200-600 kg (450-1300 lb). Disk blades are available
with either plane bevel or notshed edges.
Since the rear wheel must carry most of the side thrust of
the plow, its correct adjustment is crucial. Disk plows can be
used as two-way plows if the blades are mounted so that they
can be rotated about vefiical axes to face either the right-hand
or the left-hand sides of the plow.
4.11 Laylug out a
field for plowing
Since moldboard and disk plows not only invert the soil, but
move it laterally, the field must be laid out with forethought.
Plowing is most efficie,nt if the field is divided into rectangular
lands as illustrated in Figure 4.21. A land should be at least
three times as long as it is wide. It is easier to plow a few long
furrows than many short ones.
First, the turning areas, called headlands, are laid out.
Headland width should be twice the length of the tractor and
plow. Most plows throw the earth to the right. In each land
there will be an undesirable back furrow at the center and a
dead furrow on each side. A dead furrow is an unfilled trench.
A back furrow is a ridge made by throwing a furrow slice on
unplowed ground.
One method of laying out a field for plowing is to first
plow from A to I3 (see Fig. 4.21) and then from 13to A, creating
a back furrow. Plowing continues clockwise. Turning is done
on the headlands with the plow raised off the ground. When
a land is finished, dead Furrows will be at C-E and D-F. The
headlands are plowed after all the iands have been plowed.
For a novice farmer with a small plot, it is a good idea to
begin plowing on one side-D-F or C-E, for example-and
then deadhead back to the starting point and plow the field
in only one direction. One back furrow and one dead furrow
will result from such a plowing plan.
4.12 Rotary tillage
Rotary tillage tools include spading machines, vertical axis
rotary tillers, and horizontal axis rotary tillers. The spading
machine is a complicated device that mechanically emulates
the action of a spade as used by a human. The spading
machine makes it possible to r.inw wet, clay, uplacd soils
4.21. Plowing a land.
eadland A
lsadland e
Back f&row
without traction problems since it requires little or negative
tractor draft. Although spading machines have been used in
Great Rritain, they have not been accepted in other areas
because of their slow speed and high cost.
The vertical axis rotary tiller, when used with pedestrian
tractors for once-over land preparation, does not leave a flat,
even seedbed like the horizontal axis rotary tiller. Nowever,
it is useful for creating ridges and hilling LIP row crops. Some
power harrows (discussed subsequentlyi are verficai axis
rotary tillers, but they are designed fo: secondary rather than
primary tillage.
The tillage tines for mounting on the axle of the singleaxle pedestrian tractor ir. Figure 2.3, and the tiller shown on
the double-axle pedesrrinn tractor in Figure 2.5 are horizonral
axis rotary tillers, which have found wide acceptance. The
horizontal rotor machine in Figure 4.22 is the best generalpurpose rotary tiller for farm tractors, and is practically the
only type in use today. The larger rotary tillers for use on farm
tractors are discussed in this section.
A comparison of the operating characteristics of three
tractor-mounted rotary tillage machines and a two-bottom
4.22. Tractor-mounted
rotary tiller.
moldboard plow is made in Table 4.5. The spading machine
had a working width of 6 ft ( 1.8 m), and the two rotary tillers,
5 ft (1.5 m>. The vertical rotor machine in Table 4.5 was a
heavy-duty rotary tiller designed for primary tillage.
The rotary tiller has two unique features: 1) it combines
primary and secondary tillage in one operation, and 2) it
provides negative draft, since the rotor and the earth-engaging tines rotate in the same direction as the tractor wheels. The
rotary tiller is powered by the tractor’s PTO. When the tiller
is working! it exerts a forward push on the tractor. The tractor
retards the push of the tiller by means of soil resistance to the
tires, transmission, engine, and brakes. If the transmission
clutch is disengaged while the rotary tiller is working under
full power. the absence of the restraining force of the tractor
Table 4.5. Rotary tiller performance on clay soii with crop residue.’
Workmg Rotor
de;?% in speed
inches (cm) (rpm)
Horizontal rotor
Vertical rotor
Spading machine
moldboard plow
4 (10)
4 (10)
8 (20)
8 (20)
mph (km/h) hp
Draft in
lb VW
1 (1.6)
1 (1.6)
1 (1.6)
25 (111)
230 (1023)
200 (890)
3 l/2 (5.6)
2100 (9340)
wheels causes the tractor to accelerate. The tractor must be
operated with direct-drive transmission gear, and not with a
freewheeling transmission.
The once-over feature of the rotary tiller is advantageous
because only one implement is required for tillage. The
disadvantage, however, is that combining several energy
intensive jobs into one creates the need for I large tractor. The
rotary tiller uses about three times as much energy to move
and pulverize 1 cm’ as does a moldboard plow. The
combined energy requirement for plowing with a moldboard
plow, disking, and harrowing may be less than that required
by a rotary tiller. For example, a 200-cm (79-in) tiller operating
13 cm (5 in> deep in a medium soil at 5 km/h (3 mph) requires
a 1.25-hptractor. Higher speed, greater tillage depth, heavier
soil, and increased rotor speed for finer soil partic!es require
greater horsepower. For this example, the tilling rate is 0.7
ha/h (1 3/1 acres/h).
Since tractor and rotary tiller movement do not depend on
traction, the tractor does not require the additional weight
used to provide greater draft. As a result, a tractor powering
a rotary tiller can have very good flotation. When a rotary tiller
is used for puddling ricefields, the tractor has all excessweight
removed and becomes little more than a steerable engine for
the tiller.
Except for puddling ricefields, there is danger iti working
wet soils with rotary tillers. Since traction is not a problem,
it is tempt,ing for the farmer to begin working the soil before
it is properly moist. Sandy soils do not pose a serious
problem, but clay soils have a moisture range over which a
rotary tiller cannot easily do a satisfactory job (moldboard or
disk plows are preferable). Many clay soils are dry on the
surface. while the soil lo-15 cm deep is quite wet and plastic.
If a clayey soil in this condition is plowed with a moldboard
‘nordisk plow, the soil is inverted, and by the time the new
Surface soil dries, the secondary tillage can be accomplished
with a disk harrow or spring-tooth harrow. If this wet, clayey
soil is tilled with a rotary tiller, however, a very undesirable
seedbed filled with mud balls and clods is created. A farmer
using a rotary tiller to prepare a clayey soil under wet
conditions for upland cultivation must exercise caution.
Excessive pulverization of the soil under optimum soil
moisture can occur if rotor speed is too fast, forward speed is
too low, soil shield is set too low, or there are too many lines.
Excessive soil pulverization can damage soil structure below
the surface and create crusting on the surface. Rotary tillers
are not usually used in stony soil because of the high cost of
tine replacement and excessive machine wear.
Tines are usually L-shaped. L tines work well in heavy
trash. C-shaped rines are more curved than the L tines and
are useful in penetrating hard soil or in alleviating rotor
clogging in wet, heavy soils. Straight, thin tines are sometimes
used to reduce power requirements when breaking clods and
removing weeds in secondary tiliage. Tines are usually
bolted to flanges attached to the rotor and are attached in pairs
of left-hand and right-hand tines.
Combinations of short and long tines can be used for strip
tiilage. For example, long tines are spaced along the rotor to
till narrow strips where seed is planted, while short tines are
attached to the rotor between the long tines. The short tines
remove weeds and mulch on the surface, while the longer
tines prepare the seedbed.
The spiral plow is a tiiiage implement for a single-axle
pedestrian tractor and is used primarily for tiilage in flooded
ricefields. It consists of a right-hand and a left-hand auger,
mounted on the axle in place of the cage wheels. The augers
move the soil toward each side of the tractor, and the comb
harrow smooths and levels the earth and stubble loosened by
the spiral plow. A typical jpirai plow has an outside diameter
of 41 cm (16 in) and a width of 57 cm (22 in). Soil tiith is
regulated by braking the tractor with the comb harrow to
adjust forward speed-the slower the speed, the finer the tilth.
In soft mud conditions, the spiral plow is more difficult to turn
than a pedestrian tractor equipped with a moldboard plow or
a double-disk plow. Research in the Philippines in which
implements mounted on single-a& pedestrian tractors were
compared in tilling ricefields with a “normal depth of soft mud
layer” revealed that the moldboard plow had a capacity of 0.1 I
ha/h; double-disk plow, 0.14 ha/h; cage wheels and comb
harrow, 0.15 ha/h; and spiral plow, 0.15 ha/h. In deep soft
mud, the disk plow and the spiral plow bogged downs
4.13 Harrows
Harrows, classified as secondary tiilagc implements, are used
to prepare seedbeds) remove weds, break crusted soil, and
aerate pastures. The primary types are the spike-tooth,
4.23. Triangular harrow.
spring-tooth, chain link, disk, and power harrows. Spiketooth harrows are also called peg-tooth, drag, zigzag, section,
or smoothing harrows. Rotary and reciprocating harrows can
be powered by the tixtor PTO. Ail harrows are pulled as draft
The comb harrow, a one-bar spike-tooth harrow, is
described in the section on puddiers, since it is used exclusively for preparing fields for wetland rice cultivation. Another type of simple spike-tooth harrow for upland tiliage, the
triangular harrow, is a spike-tooth harrow with pegs (teeth)
set into a triangular frame (Fig. 4.23). The working width is
1.5 m, and the harrow is often animal drawn. In primitive
agriculture, both teeth and frame are made of wood, while
factory-built triangular harrows are usually mlde of steel.
The spike-tooth harrow consists of steel teeth, rectangular
in cross section, set vertically into a horizontal frame so that
they form a zigzag pattern to prevent the rear teeth from
following in the tracks of the front teeth. These harrows range
from 1 to 9 m in width, with teeth 16-20 mm square. A heavy
harrow used for crumbling clods carries about 2 kg of frame
weight per tooth. Lighter harrows, called tine-tooth harrows!
have wire teeth up to 75 mm in diameter and weigh about 0.5
kg per tooth. Tine harrows are used for final seedbed
preparation or for breaking crusted soil.
The basic unit of spring-tooth and spike-tooth harrows is
called the section, which is a rigid frame 1.2-2.2 m wide.
Open-ended frames have only front and side frame members,
while closed-ended frames feature a rectangular frame. The
4.24. Spring-toothharrow.
closed-ended frame is stronger, but the open-ended frame
allows less clogging by surface debris. Sections can be hinged
together to form a wider harrow. I-Iarrows are easily shipped
by sections, and harrow width can be quickly adjusted for use
in uneven fields.
Harrows work up to 10 cm deep. The frame must be
pdraliei to the ground for best results. When preparing a
seedbed, a scrubber board is often attached to the front of the
harrow, and a drag or crumbier to the rear to obtain a smooth
surface for planting small seeds.
The spring-tooth harrow (Fig. 4.24) has deeper penetration and more aggressiveness toward weeds than the spiketooth harrow. It is better than the disc harrow in stony
conditions, but plugs in heavy trash. A spring-tooth harrow
has three to six sections, and three toothbars per section. It
has teeth on 30-cm spacing, providing a working tooth every
10 cm. Teeth are made of spring steel, 8 x 44 mm in cross
section. Ail the teeth can be pivoted with a single lever. FOI
light surface harrowing with little soil penetration, the working tips of the tines are vertical; for deep, aggressive work, the
tips are nearly horizontal. Heavy-duty wheeled spring-tooth
harrows are made in widths ranging from 3.5 to 12 m.
A chain-link harrow, shown in Figure 4.25, has no rigid
frame. It is woven from l- to 1.5cm steel wire into links like
a wire mesh fence. Aspiked tooth extends from f2dch link. For
aggressive action, the harrow is laid out with the spiked teeth
down. For less aggressive action, the harrow is flipped over.
Sections are 1.5 m wide, and assembled harrows consist of l6 section,s. A pipe across the front of the woven net of chain
links serves as the drawbar. The chain harrow is useful for
pesticide incorporation and pasture aeration as well as
seedbed preparation. It hugs the soil surface better and is less
expensive than other harrows. A disadvantage is t,hdt some
models are difficult to lift and move because of the lack of a
Disk harrows are used for seedbed preparation, chemical
incorporation, weed control, and disking heavy crop residues
before plowin_: The tandem disk (Fig. 4.26) is developed
4.25. Chain-link harrow.
4.26. Tandem disk harmw,
Illustration courtesy of Deere 8 Company
from the single-action disk Wig. 4.27), and the double offset
disk from the single offset disk (Fig. 4.28). Rear blades of a
tandem disk are set to follow half-way between the front
blades. The disk blades rotate as the disk is pulled along. The
action of the disk on the soil depends on the diameter of the
disk blade, the weight of the disk , and the disk gang cutting
Disk blades are 35-80 cm in diameter. Blades of 40-50 cm
diameter are popular for horse-drawn I:.iisks,while 45 to 80cm-diameter blades are used for tractor-drawn disks. The
4.27. Disk harroirv (single
4.28. Offset disk harrow.
Illustration courtesy of Ford New Holland. Inc.
disks are conical or spherical in shape and are mad? of heattreated high-alloy steel. Disk biades are made both notched
(scalloped) and plain. Notched blades penetrate and cut
through trash such as nlaize stalks better than plain disks.
Disks are &sembled from right-hand and left-hand gangs.
A single-action disk consists of a right-iTand and a left-hand
gang. The side draft of one disk cancels out the side draft of
the other. A single-action disk harrow with the convex sides
of the disks toward the center moves earth outward from the
ends of the harrow. By reversing the left-hand and right-hand
sections so ,that the convex sides face outward, two singleaction disks can be placed in tandem. Thus, the rear blades
move the earth back to its original position. The disk gang
cutting angle is the angle between a line perpendicular to the
disk axle and the line of travel. The angle can be varied from
about 10” to 25”. On an offset disk, the angle may be as much
as SO”. Increasing the cutting angle provides increased
penetration, trash cutting, and covering, but requires greater
draft force. Penetration depends primarily on weight per
blade, while seedbed fineness depends on blade spacing
(Table 4.6). Ballast can be added to disk harrows to increase
weight. Alternately, weight transfer hitches are available for
adding tractor weight to the harrow by means of hydraulic
An offset disk harrow is a single right-hand or left-hand
section that utilizes side draft to offset the harrow from the
tractor track. With an offset disk harrow, it is thus possible to
disk under trees too low to permit a tractor to pass. When
right-hand and left-hand offset disk gangs are connected in
tandem, the side forces cancel, and the implement runs on the
tractor track. If it is necessary to operate a tandem offset disk
off to the side of the tractor, one can offset, the tractor hitch
up to about half of the desired offset and obtain the remainder
Table 4.6. Typical disk harrow b:ade spacing and weight per unit
length of gang.
Disk blade diameter
Blade spacing
Weight per unit length
80-l 60
225-375 150-270
by running the rear offset disk at a shallower depth. Heavy
offset disk harrows with large disk blades (8 mm thick, 80 cm
diameter) are commonly used for clearing land as well as for
primary tillage. In North America, these heavy offset clisks are
commonly called Rome plows. Disk harrows can work
deeper and pulverize the soil better than t,he spike, springtooth, or chain-link harrows, but require much more power
per unit of width.
The power harrow is a tractor-mounted, single-pass
secondary tillage tool that uses power from a tractor’s PTO to
drive the harrow tines in a reciprocating or a rotary motion.
Power harrows stir the soil and are used primarily to form
seedbeds for vegetable crops and to incorporate herbicides.
The power harrow replaces separate operations with disk
harrows and spring-tooth or spike-tooth harrows. Speed is
approximately 5 km/h, depending on available power and
desired soil tilth. In light soils, the power harrow may also he
used for pasture reclamation and primary tillage. Working
depth is controlled by adjusting the height of a crumbler roller
or by depth-control wheels supporting the rear of the
Since the soil-engaging tines of a power harrow are
powered by tlic- PTO, less traction is required at the tractor
drive wheels. This allows the reduction of tractor ballast, and
thus increases tractor flotation. There are four generic types
of power harrows: reciprocating, rotary, semirotary, and
The reciprocating power harrow (Fig. 4.20) is probably
the most common power harrow. It has vertical spike tines
attached to horizontal tine bars. The soil is stirred by the
interaction of the sidewards reciprocating movement of the
tines and the forward movement of the tractor. Typical
reciprocating power harrows have 25-&long tines 18-30 cm
apart on tine bars 2.5 to 5 m long. Most reciprocating power
harrows have two tine bars, although four-tine bar units are
available. A 3-m-wide , ‘-bar reciprocating power harrow
weighs 500 kg, requires a 70-hp tractor, and travels about 5
km/h. The slower the speed, the finer the tilth. Steel scuffingboards are clamped to the reciprocating tines to provide a
smoother seedhed.
Kotaly power harrows have two or three long tines on
vertical rotors and provide a rotary stirring of the soil as the
4.29. Reciprocatingpower
trxtor moves forwxrc!. The semirotary !~mmw is ;I cross
txtwern the rotary and die Pairs of tines
are clriven through an oscillating bearing. The spike-rotor is
the simplest power harrow. It is a pmvered rotor with spike:;
projectin:: radially from the rotor. In genera!. the spike-mtor
tends to invert the soil more than the other types of power
harrows and does not prep:me as fi,lt’ :I seedlxd.
Suifxe rrash such as straw, smvrr. and potato h;~utm
xtverxly affects power linrrow perfornxlnce txcause, unless
it is well chopped. the trash will catch in the tines, t~und~
Ixtween bars, or wrap on rotrrry hcxls. I%wc:r harrows :I~Y
also prone to ttarna~e by stones. which can bend or snap tines.
In nonstnny soils, tines shoulct last from 20 ha on dxisive soil
to 200 ha on silt.
When rnatchin~ :t rot:uy power harrow to a fmn tractor,
a rule of thumt~ is that 23-30 nixknuni IT0 lip/m (7-Y tlp/ft)
width is requircct for satisfxtory oper;ktion. For example. ;t
2.5-m (8.2~ftb-wide power tiller requires :I 60-hp trxtor.
Crops such as cass3\q potato, mnize. yam. etc. xt’ grown
on ridges or kis in some f:irming systems. The top of ;I ridge
is only wick cnou~h to :iccommod;~t~!one row of plants. while
:I kt has sufficienr kvidth for two rows of ptx~ts. Witcr is kc!
into the ditches betnecn tile ridges or ixtls in irri~atcd
farming systems. Ridgers-also known as middlebreakers or
ridging plows-are used to make the ridges. In light soils the
ridges are made without prior tillage, but in heavier soils or
in soils with heavy crop residue, the field is tilled to obtain a
good seedbed before ridging. The moldboard type riclger is
a plow point with both a left-hand and a right-hand moldboard (Fig. 4.30). They are made in both single-ridge, animaldrawn as well as multiridge tractor-mounted units. Disk
ridgers and disk bedders consist of convex disks mounted on
a too! bar, set at an angle to the direction of travel, and spaced
so that adjacent disks throw earth into a ridge between them.
In some farming conditions where there is a minimum of
moisture, the seed is planted in the bottom of the furrows
lnade with the moldboard-type ridger. This is called lister
planting. If the ridger and the planter are combined into one
implement, it is called a lister.
Rotary ridging blades as shown in Figure 2.3 can also be
used to form rough ridges with a pedestrian tractor. Each pass
of the tractor forms one-half of each adjacent ridge.
The skies and tops of ridges or beds for small-seeded
vegetdbks are often formed into a uniform cross section with
a tractor-drawn sled or with rotary bed farmers. The sled-type
4.30. Tractor-mounted
moldboard-type ridger.
is merely a sled with “tunnels” that have the cross sectional
shape of the ridge or bed. The rotary type consists of a drum
about I m in diameter and grooves of the desired
ridge or bed cross section. Ridge formers usually form at least
four ridges or beds per pass and are frequently hitched in
tandem to the ridger.
4.14 Puddlers
Land for wetland rice is often flooded for 1-4 wk prior to
plowing and puddling, to weaken the mechanical strength of
the soil. By retaining standing water on the ricefield, the
farmer receives the benefits of weed control, oxidation
reduction conditions that favor nutrient balance, and a soft
soil into which to plant rice seedlings.
Puddling helps retain standing water in the ricefield by
producing fine soil particles that reduce soil porosity, thus
reducing seepage. Puddling is also beneficial because it levels
the soil surface and provides a homogenized soil with no
clods. Puddling must be done when there is stallding water
on the field. In wetland ricefields, the very conditions that are
disastrous for other crops are desirable.
The simplest method of puddling is done by the farmer’s
feet. Holding a staff in both hands for b:alance, the farmer
works his feet up and down to break clods into smaller pieces
and to smear and compress the soil. A herd of three to five
water buffalo is sometimes used for puddling. The animals
are driven around and around in the field so that their hooves
shear and compress the soil and break down the soil
aggregates. Most puddling is done with an animal- or tractordrawn implement such as the comb harrow, ladder, or rotary
The comb harrow (Fig. 4.31) is a single-row spike-tooth
harrow made of wood and steel with no moving parts. It is
lightweight (10 kg) and is easily carried. A typical comb
harrow is 1.2 m wide and has 13 tines 25 cm long. Comb
harrows designed to be pulled by water buffalo have a top
horizontal handlebar by which the farmer can chmge the
penetration angle of the teeth. This is accomplished by
rocking the handle bar backward to increase the aggressiveness of the teeth, or forward to allow weeds to slide off the
teeth and thus obtain a soil-smoothing effect. The farmer
adjusts for the amount of earth to be moved when puddling
and leveling a wetland field in much the same manner. In a
4.31. Comb harrow pulled
by water buffalo.
flooded field, a con~bharrow requires approximately 2546 kg
of draft per meter of width, dcpenclin,g on whether the soil is
soft or hard.”
Conib harrows for pedestrian tractors have the same tooth
spacing xuxl width as those fc,r the water buffalo, but lack 3
handlebar for the operator. The harrow is held to the tractor
by a pin, and the operator changes the aggressiveness of the
harrow hy vertical force on the tractor handlebars. The interaction of the mmb harrow and the tractor’s cage wheels
provides good puddling action.
Puddling ladders are wooden and about 1.5 ni (5 ft’) wide.
The farmer often stands on the ladder to increase the
aggressiveness of the device. as shown in Figure 4.32. The
ladcier does a good job of leveling as well as puddling, Ixit
works best where the standing water is only a few centimeters
deep. Ladders are freqrlently used in Bangladesh,
4.32. Ladder pulled by a
pair of small bullocks.
Rotary puddlers pulled by pedestrian tractors usually
consist of a simple frame with one ol’ two transverse lugged
rollers. The rollers are 15 cm in diameter and have flat, steel
lugs 5 mm thick and 8 cm w’ide. The lugs are welded radially
along the rollers at 90” spacing. The resistance of the lugs in
the soil rotates the rollers. The IRK1corm-puddler, illustrated
in Figure 4.33, utilizes conical-shaped rotors :nade of sheet
4.33. Cone-puddler
attached to a pedestrian
steel to create a horizontal back-and-forth action through the
top IO-cm soil layer for thorough puddling with minimum
energy. The rolling action of the cones pushes and buries
surface weeds and trash in the mud to leave a well-puddled
soil. Although the cone-puddler performs well, it has not
received wide acceptance because of its high cost. One- and
two-gang cone-puddlers are also designed to be drawn by
water buffalo. A typical cone-puddler requires a draft of 3090 kg (65-200 lb, 295-885 N), depending on soil hardness.
1. Ma C Fengchow, Takasaka T, Yang Ching-wen (1958) A preliminary study
of farm implements used in Taiwan province. Joint Commission on Rural
Construction, Tiapai, Taiwan.
2. Food and Agriculture Organization (1976) 1Mechanization of rice productioQ - India - Nigeria - Senegal, International Coordinated Research Project
1970-76. Rome.
3. Raymundc J (1981) El Khuki. Minka. Nol. Com. Coxdinadora
Adecuada 1(2):10-l 1.
4. Hopfen H J (1969) Farm implements for arid and tropical regions. PA0
Agric. Dev. Pap. 91. Food and Agriculture Organization, Rome. p. 46-55.
5. von Rau L (1882) Verzeichniss der Modell-Sammlung van Handgerathen
und Plugen nach ihrer geschichtlichen Entwicklung (Register of the model
collection of handtools and plows according to their historical development). No. 184, p. 11. Frankfurt am Main.
6. Hansen H-O (1969) Experimental ploughing with a dostrup ard replica
Tools Tillage 1:2.
7. Pascal J A (1967) Rotary soil working machines. Farm Mech. 19(211):2429.
8. Calilung E J (1,985) Comparison of land preprtration equipment used on
small rice farms in the Philippines. Thesis No. AE X5-2, A.sian Institute of
Technology, Bangkok. p. 43-48.
9. Department
of Agricukural Engineering (1986)
1986. lntemationai Rice Research Institute. P.O. Box 933,
Manila, Philippines. (unpubl.)
Bailey L H (1908) Cyclopedia of American agricutturr. Vol. 111.Animals. The
Machiibn Co.. London.
Campbell J K. Young D I-l (1984) Development of a muck-land ridger for
lettuce production.
ASAE Paper No. NAR84-101. University of Maine,
Orono, Maine.
Kline C K, Green D X G, Donahue R L. Stout H A (1969) Agricuhlrd~
mechanization in equatorial Africa. Res. Rep. 6. Institute of International
Agriculture, Michigan State University, Michigan.
5 Planting
Planting seed requires
a opening a hole or I‘urrow of proper depth,
metering the seed,
placing the seed,
covering the seed, and
firming the seedbed.
Tool or machine selection for planting seed depends on
the size of the seed and whether the soil has been tilied. The
term no-tillplanting is used when planting seed in untilled
5.1 Tools for planting
large seeds
5.1. Machete.
Large seeds include those of maize, beans, squash. pea,
peanut, and cotton. They are easier to plant than small seeds,
since individual seeds can easily be separated by human
fingers or mechanical devices. Furthermore, large seeds do
nor usually require as fine a seedbed a.sdo small seeds.
Manual tools for planting large seeds include the machete
(Fig. 5.11, dibble stick (Fig. 5.21, jab planter (Fig. 5.31, rotary
jab planter (Fig. 5.4!, and push drills.
In parts of Africa where shifting agriculture is practiced,
maize is planted immediately after burning. The farmer flicks
the forward end of a machete into the soil, twists slightly, and
withdraws it in a continuous movement. At the same time, he
drops several maize kernels into the hole with the other hand.
5.2. Dibble stick.
5.3. Jab planter.
5.4. Rotary jab planter.
As the farmer steps forward to plant the next hill, he covers
the seed and firms the soil with his foot.
The dibble stick is merely a stick to make holes in the soil.
Its conical point requires less force to penetrate the soil than
a blunt stick. The planting sequence is the same with a dibble
stick as with a machete.
The jab planter (Figure 5.3 is commonly used in the
Americas. It is a manually powered machine about 85 cm
,iong and weighs 3.2 kg when filled with 1 kg of maize seed.
At the bottom of the seed hopper is the seed plate. This can
be adjusted to provide the correct hole size to accommodate
the vge and number of seeds desired. A typical jab planter
forms a rectangular hole in the soil about 2 x 7 cm in cross
section and up to 5 cm deep. The farmer carries the jab
planter like a walking cane. Sticking the pomt into the earth
and using the hole as a pivot point, the farmer pivots the
planter forward about 30”. A spring-loaded foot connected to
one side of the point provides relative motion to open the jaws
of the point about 3 cm. The seedsdropped through the seed
plate during the previous planting cycle fall into the hole. As
the farmer pivots the planter back to a vertical position, a rod
connected to the foot rotates the seed plate one notch. The
seed falls from the seed plate cell and is retained by the closed
jaws of the point. The kernels fall into the space formed by
the closed jaws and are ready to be planted in the next cycle.
m-row and between-row spacing, as well as the straightness
of rows, depend on the farmer’s skill. Some jab planters have
hoppers for both seeds and granular fertilizer so that fertilizer
can be dropped along with the seeds.
The rotary or multiple jab planter essentially connect~ssix
jab planter mechanisms to a single seed hopper. As the rotary
jab planter is pushed along the row, a cam opens and closes
the jaws of the six points. Instead of having to carry the
planter, the farmer pushes it along. The depth of penetration
of the points depends on soil conditions and the weight of the
planter. Frequently, it is necessary to add weight to the rotary
planter in order to obtain proper penetration. A minor
disadvantage of the rotary jab planter is that in-row spacing
cannot be altered.
An animal-drawn ard is commonly used to form a furrow
for seed. (In many societies, the seed is dropped into the
furrow by a woman in the belief that seed planted by a female
is more productive than seed planted by a male.) The
plowman then covers the seed with the ard.
One-row planters that can be pushed by one person differ
significantly. An example of a simple one-row planter is a
wheel with a seed hopper at the hub. The seeds fall from
adjustable holes as the wheel is pushed along the furrow. An
example of a more sophisticated one-row planter is one that
uses the same type of metering plate mechanisms used on
animal- or tractor-drawn planters.
In India, multitube seed drills wherein three to six seed
tubes direct seed behind a furrowing bar have been used for
hundreds of years.’ The seed tubes radiate from a single
wooden bowl where the farmer’s hand swirls the seeds into
the seed tubes. These drills (illustrated in Fig. 5.5) can be used
only on soil that has been plowed and harrowed.
An animal-drawn, one-row walking planter (shown in Fig.
5.6) has a simple steel frame and weighs about 50 kg. A sulkytype two-row planter weighs about 250 kg, excluding the
weight of the tongue. Planters for tractors are either trailed
machines very much like animal-drawn planters, integral
units, or one-row tool bar-mounted trailing type units. The
integral units are mounted on the tractor frame. The one-row
trailing type units are more popular. since they fasten to a tool
bar on the tractor’s three-point hitch and can be easily
adjusted for row spacing, being usually ground-driven. The
trailing type is easy to mount and to use. One- and two-row
planters of either the mounted or the trailing type use manual
5.5. Indian seed drill.
5.5. Animal-drawn one-row
or hydraulic lift mechanisms. Multirow units are usually lifted
with the tractor’s hydraulic system.
The seed metering system separatesone seed and delivers
it to the seed-placing mechanism or furrow at a selected rate.
If maize is being planted at the rate of 50,000 kernels/ha
(20,00O/acrej at an in-row spacing of 27 cm, in rows 75 cm
apart and at a forward speed of 8 km/h, the seed metering
system must select and drop a seed each eighth of a second.
The seed plate system has been used for many years as the
metering device for planting large seeds. For best operation,
the seed plate requires seed graded according to size.
Plateless seed metering systems utilizing mechanical pickup
fingers, vacuum, or air pressure to meter the seeds are
gradually replacing the plate type planter because they can
plant ungraded seed at high speed.
A typical air seed-metering device is shown in Figure 5.7.
A fan pressurizes the air in the seed chamber, which is on one
side of a rotating vertical seed disc. The air pressure
differential between the chamber side and the outside of the
seed disc holds one seed in each hole of the !jeed disc. At the
point where the seed disc is to drop each seed into the seed
tube, a roller or asliding plate along the outside of the seed
disc eliminates the pressure differential across the seed disc,
and the seed falls down the seed chute into the groove made
in the soil by the opener. The seed mechanism is usually
placed as close to the soil as consistent with good design, for
with a short seed tube the fal!ing seed will be at a low velocity
and will not bounce when it strikes the soil. Figure 5.7 shows
a runner-type opener on the planter.
The no-till planter (Fig. 5.8) is actually~a misnomer, since
it cultivates the soil, preparing a lo-cm-w~ide strip just ahead
of the planting shoe. A planter that is designed for planting
on tilled soil will not operate satisfactorily on untilled soil;
5.7. Air seed-metering
5.8. No-till maize planter.
however, a no-till planter does a satisfactory planting job on
both tilled and untilled soil. The functional elements of a notill planter are shown schematically in Figure 5.9.
TIie.~~tilis~ropelzer is usually the first soil engaging tool,
because the fertilizer is positioned in front of the planter to
place the heavy mass of fertilizer close to the tmctor. Plain
double-disc openers are generally c,sed to make the slot for
dry fertilizers, although single-disc or runner openers are
sometimes used. Discs often perform better than runners.
Discs can usually be set 5-15 cm to the side of’ the seed row.
Tr~zshdiscs are mounred ahead of the tillage disc to push
crop residue off the strip where the seed is to be planted. The
absence of crop residue on top of the tilled strip makes for
more uniform seed placement. In cool climates. the use of
trash discs can also rttise the soil temperature and enhance
uniform seed germination.
The tillage nzecl7urrism
tills the na!row strip of soil where
the seed is planted. Fluted or ripple disc coulters are most
common, although chisels or powered rotary tillers are used
on a few designs. Disc coulters are usually 17 in (43 cm) in
diameter and till to a depth of IO-13 cm. The fluted coulter
tills a IO-cm-wide strip. while the ripple coulter tills a 2- to 4..
cm strip. The ripple coulter requires less down force than the
fluted coulter. On hillsides, however. where the wider strip
is an advantage, and on drier soil, the fluted coulter is better.
The ripple x~ulter is best suited for use on wet,, trash-covered
soils. The fluted coulter tends to push residue down into the
.Q. Sequence of soilngaging elements of a noII maize planter. 1 = fertil:er opener, 2 = trash disc,
= tillage mechanism,
= seed opener and depth
auge, 5 = seed firming
#heel,6 = seed coverer,
= press wheel.
wet soil, thus minimizing good soil-seed contact. Chisels are
the least costly mechanisms. Powered rotary tillers prepare a
fine strip seedbed, but they are expensive, must be powered,
and have higher maintenance costs than other types of tillage
The seed opener is a conventional double-disc, singledisc, or runner opener that can be used with planters for both
plowed and tilled soil. The depth gauge is usually a rim
mounted on the seed opener disc. Planting depth is the
difference between the radius of the disc seed opener and the
radius of the depth gauge rim.
The seedfirming wheel is 1530 cm in diameter and about
2 cm wide. The firming wheel presses the seed to provide
good seed-soil contact before the seed is covered with earth.
It cannot be used in sticky soils because the soil sticks to the
firming wheel and moves the seeds out of position.
The seen’coverer is either a disc or a &de. Its purpose is
to cover the seed with fine soil particles. The press t&&then
firms the soil on top of the seed. in a well-tilled seedbed, a
seed-firming wheel is unnecessary. since the press wheel is
sufficient. The press wheel is frequently designed to function
both as a depth gauge and as a power source for individual
crop planter units.
In addition to the parts of a large seed planter mentioned
above, an insecticide applicator or herbicide applicator may
be mounted in the rear and driven by the press wheel. A disc
coulter on the end of an adjustable boom is often used as a
but this is often unsatisfactory in trashy conditions. A better method of marking rows is obtained by
suspending a chain in front of the tractor. When the chain is
kept over a previously planted row, the spacing is correct.
TOW marker,
5.2 Tools for planting
Rice, wheat, sorghum, mustard, and alfalfa are examples of
crops with small seeds. Broadcasting, drilling, and precision
drilling are the methods normally used to plant small seeds.
Dry, viable, ungerminated seed is almost always used for
The principal exception is the direct seeding of wetland
rice, Lvherethe soil is water saturated. Seeds require oxygen
to germinate. Since a flooded ricefield is anaerobic, rice seeds
must be soaked in water for about 36 h before planting to
pregerminate them. If pregermination goes too far, the
sprouts may be killed by being broken during planting. To
plant pregerminated rice seed, the soil must be saturated to a
soft mud consistency, but without pools of standing water.
Good water control is essential in planting pregerminated
Broadcasting is an ancient method of planting small seeds
and can be done without equipment as shown in Figure 5.10.
5.10. Ethiopian farmer
broadcasting wheat.
. .
-. ---__
._ --1_
. .._
_, - ._:
. .-_. .
- .-- ---.,--_,.:-:, -. -. \ L
. .-_.
_. -
After the: seed is broadcast, it is usually work& into the soil
to obtain better seed-soil contact and thus better germination.
The Ethiopian farmer covers the seed by an additional
plowing with his beam ard. Sometimes a tree branch or a
spike-tooth harrow is trailed behind a yoke of bullocks to
work the seed into the ground.
A cyclone seeder is a manually powered centrifugal
seeder powered by a hand crank or reciprocating bow to
broadcast grass and other small seeds. Larger spinner-type
centrifugal seeders can be mounted on a tractor’s three-point
hitch and powered by the PTO. Airplanes are sometimes
utilized to broadcast seed onto large fielcls. If soil moisture
and growing conditions are conducive to germination and
growth, or if the terrain is difficult for ground equipment, no
effort is made to cover the seed. Otherwise, the seed can be
covered by passing a harrow over the field.
Weed control is often a problem in fields planted by
broadcasting, since mechanical weeding equipment cannot
be used, and hand-pulling is too time-consuming. Planting by
broadcasting therefore often requires chemical herbicides for
weed control.
Small seeclscan be planted in rows by dropping the seeds
individually into a furrow made by a farmer with a hoe! by an
animal-drawn ard, or by a simple multirow furrower drawn by
an animal or tractor. The seed must be covered both to obtain
good earth-seed contact and to protect it from birds. The seed
is covered by a worker using his foot, by a hoe, or by an
animal- or tractor-drawn plank or harrow.
The g?~irz d?Y/!(Fig. 5.11) is the most common impkment
for planting small grain. Whether drawn by animal or tractor.
drills are essentially the same. They consist of a box to hold
the seed, a seed-metering device, furrow openers, a seedcovering device, and clrive wheels to power the seedmetering device. Grain drills are differentiated by their
number of furrow openers and the space between furrows.
For example, a 27-7 drill has 27 furrow openers spaced 7 in
(18 cm) apart. Thus it will seed a width of 15 ft 9 in (480 cm).
Drills are available with furrow opener spacing of 6-14 in (I$
35 cm). Fertilizer, grass-seeding, or no-till attachments can be
added as options.
The seed-metering device must transfer seed from the
seedbox to the coulter tubes at a fixed rate and yet be easily
5.11. Graindrill.
adjusted for a variety of grains. The number of individual
metering devices should equal the number of coulters. The
external force feed is one of the most common devices and
works well over a wide range of seeds (Fig. 5.12).
The external force feed consists of a metal roller with a
sqtiaie bore and external flutes over half its length. Each roller
fits into a feed cup, which is attached,to the bottom of the seed
box. A square shaft driven by the drill wheels extends through
the fluted rollers and drives them in relation to ground speed.
An adjustable gate regulates the size of the passagebetween
the output side of the fluted roller and the drop tube to the
5.12. Externalforcefeed.
coulter. To adjust the rate of seeding, the fluted roller is slid
axially on the square shaft so that the unfluted area exposed
to the feed cup opening is increased or decreased. When the
unfluted area is exposed to the opening, no seed wili flow.
When the fluted area is exposed, the seeding rate is maximized. Feed rate can also be adjusted by changing the gear
ratio of the transmission between the drill wheels and the
square shaft that drives the fluted rollers.
Another common seed-metering device on grain drills is
the internal double-run feed (Fig. 5.13), which has a double
flanged ,wheel, usually made of cast iron. One flange has
coarse internal corrugations, while the other has fine corrugations. The wheel fits into a housing attached to the bottom of
the seed box. The housing is designed so that by a simple
adjustment, seed from the box can be directed into either the
coarse or the fine side of the wheel. When planting small
seeds, the fine side is used; the coarse side is used with large
seeds. Sowing rate is adjusted by the speed of the wheel and
the position of a gate between the point where the seeds drop
off the internal corrugations and the outlet of the drop tube.
Another seed-metering device for grain drills consists of
a soft polyurethane roller set ‘against a glass or metal plate to
wipe seeds one layer thick into a drop tube.
Pneumatic drills are made in widths up to 13.4 m (45 ft)
and can be operated at high speeds while minimizing weight
and mechanical complexity. A typical pneumatic drill consists
5.13. Internal double-run
of a battery of fluted rollers, each feeding seed to a flexible air
tube and coulter. A blower driven by the tractor’s PTO
provides air pressure to send the seed through the tubes and
the coulters. Because of the velocity at which the seed strikes
the furrow, depth is more difficult to control than with a
slower drill, where seeds drop by gravity.
The drum seeder illustrated in Figure 5.14 provides a
simple method of planting presemminatedrice seed in rows so
that manually operated mechanical weeders can be used. A
rotating drum containing the seed is the heart of the drum
seeder. Around each drum are one or two rows of holes.
Space between rows is determined by the axial distance
between the rows of holes. When the holes are fully exposed,
the seeder is set at its highest seeding rate. For a lower rate,
a band is moved axially and clamped over a portion of each
hole to restrict the flow of seed. As the seeder is pulled across
the ricefieid, the drums rotate and seeds fall out of the holes.
The seed is not injected into the wetland field, but merely
dropped on top of the mud. If there is a serious bird problem
or danger of heavy rainstorms at planting time, the drum
seeder should not be used.
The drum seeder is also used to plant upland crops such
as mungbean, pea, and bean. Furrows are made with an
5.14. Eight-row drum
Seed capacity Labor requirement
Machine weight with seed
Machine length
kg (2 kg/hopper)
animal- or tractor-drawn furrower, and the drum seeder is
pulled so the seeds fall into the furrows. The seed is then
covered by foot or with a harrow. The drum seeder cannot
provide exact spacing between individual seeds, but for many
crops exact seed placement is not required.
The level of seed in the drum and the peripheral speed of
the drum as well as the number and size of hole openings
affect the seeding rate. For example, the number of maize
kernels metered by a drum seeder with lFmm-diameter holes
and operating at a peripher ., speed of 13 m/min varied frc,m
loo/rev when the drum was 80% full to 150 at 50% full to 2,40
when it was only 20”/ full. Thus, a simple drum seeder should
be operated between about l/3 and 2/3 full. With the seed
drum 50% full, the seeding rate varied from 175 seeds/rev at
a peripheral speed of 4 m/min, t,o 180 at 13 rn/min to 115 at
22 m/min.’
Fluid drilling is a technique for planting small seeds. The
seeds are mixed in a gel, which is extruded in the furrow like
a ribbon of toothpaste. Since it is the gel that is metered in
the row, the seeds cannot be placed with absolute precision.
If the seeds are mixed with even density throughout the gel,
however, the average number of seeds per unit of length can
be satisfactorily controlled. The primary reason for fluid
drilling is to improve the germination rate of vegetable crops
such as Brussels sprouts. The seeds are first placed in a
solution of water and salt so that a density difference separates
the viable seed from the dead seed. The viable seed is then
mixed into a gel. The gel may be simply made from wheat
flour paste, and the planter can merely be a plastic cone used
by cake decorators. For large-scale fluid drilling, many drills
use a ground-driven peristaltic pump for each row unit.
Planning is very imporvant when planting pregerminated
seed or using the fluid drilling technique. Since the seed has
begun to germinate, it must be planted within a day or two of
the scheduled planting date. If a heavy rain or lateness of
seedbed preparation prevents planting at the scheduled time,
later planting is usually impossible, although some sophisticated fluid drilling facilities can store the pregerminated seed
in cold (about 0 “0 oxygenated water for several days.
Small seeds are sometimes pelletized so that they can be
planted accurately with equipment designed for large seeds.
Very small seeds such as petunia and SiTId irregular seeds
such as carrot, sugar beet, and lettuce are encapsulated
(pelletized) in uniform clay or sand spheroids about 3-S mm
in diameter. The technique consists of putting the seed into
a rotating drum or oscillating pan, alternately wetting the seed
with water (or a water-soluble binder such as sugar water),
and dusting it with fine day or sand. The result is a spheroid
with a seed as its nucleus.
Single-seedplanters (Fig. 5.15) are used to place seed in
rows with identical distance between seeds. The planters use
belts or discs with accurately spaced holes for holding one
seed each. Unless clean, graded seed is used, a vacuum-type
metering device is often required. These devices utilize an air
pressure differential that holds one seed in each cell until the
differential is zero. Single seed drills for planting small seed
are usually made in one-row tool-bar mounted units that are
ganged together for multirow planting. These planters are
usually operated at 3-6 km/h when planting seed with a high
germination rate. The seedbed must be well prepared in
order to plant to s&and,meaning that the plants are placed in
the row with great precision to eliminate the need to fill in
skips or chop out excess plants.
Tools for planting
cuttings and tubers
515. Single-seed planter
with seed belt metering.
CassavaUkznihot utili.~sim& also known as maniac. tapioca.
yucca. mandioca, and guac;lmotel is grown for human and
animal consumption in all tropical countries. Cassava normally produces seed. which enables plant breeders to develop varieties w?th specific characteristics. 'lh! @TlCKIl
method for propagating cassava,however, is by planting stem
sections that reproduce vegetatively. Stem cuttings are made
from plants at least 10 mo old. The stem cuttings, called seed
in some areas and stakes in others, are approximately 2.5-3.5
cm in diameter and 25 cm long. About 2/3 of the length of
the cutting is inserted into the soil. Roots develop from the
nodes under the soil, while new shoots emerge from the
node.; above, ground. In subsistence agricultural systems
where cassavais planted on mounds, a short-handed hoe is
used to prepare the seedbed and to plant the stake. In some
areas, cassavais intercropped with maize, eggplant, or other
vegetables. In others, it is intercropped wit!] tree crops such
as coconut, oil palm, or rubber.
Machine planting can be used if the cassavais planted on
ridges or in rows on the flat. For optimum root production
under a monoculture system, plant density should be lO,OOO20,000 plants per hectare.S
The cutting angle of the stake and the position of the stake
in relation to the soil surface affect the position of the roots,
thus determining the success of mechanical harvesting. The
effects that depth of planting, angle of cut> and planting
position have on root distribution are shown in Figure 5.16.
Root distribution and a,ttachment can differ among cassava
Several cassavaplanters have been developed in Nigeria.
One is a two-row, semi-automatic planter that simultaneously
makes ridges and plants cassavastakes.” The planter is carried
on two land wheels and is attached to the three-point hitch of
a category I tractor. Discs form the ridge, while an ingenious
gripping device fabricated from discarded automobile tires
5.16. Effects of cutting
angle and planting position
on cassava root position.
JO cm
Very sepwated
grips the cassavastake, places it in an upright pclsition, and
pushes it into the freshly formed ridge. Two men riding on
the planter select stakes from a box and lay them onto the
gripping devices, which are in the open position at the top of
their cycles.
Another Nigerian cassava planter is two-row and fully
automatic5 The planter is drawn by a tractor and is capable
of planting at speeds up to 10 km/h. Quality of stake
placement, however, suffers above 6 km/h. The stake angle
is affected by the speed of planting. The angle varies from 81”
at 0.5 km/h to 45” at 6 km/h and 27’ at 10 km/h. Stakesare
25 cm long. The machine requires a plowed, harrowed, level
seedbed. Discs on the planter form ridges 7 cm high and 16
cm wide. The stakes are planted to a depth of 17 cm. The
machine is designed to form a ridge around the cassavastake.
Row spacing and plant spacing within. the row are 90 cm.
is sown by planting
Sugarcane(Succharunz qffkinamm)
setts, which are short pieces of stem containing about three
nodes. A sett is 2.5-5 cm in diameter and about 30 cm long.
About 4-6 t of setts are required to plant I ha. The setts are
laid end to end in furrows at about 1.5 m spacing and covered
with 5-8 cm of earth. The goal is to produce a plant about
every 60 cm in the row. Sugarcane can be grown from seed,
but the seed has poor viability and thus is used primarily for
breeding purposes. Semimechanized planting utilizes a plow
to make the furrows and place the setts, which are covered
with earth by hoes.
Mechanical planters that form a furrow with a middle
buster are available. The setts then slide down a tube into the
furrow, and disc coulters cover them. The setts are carried
on the planter and fed into the planting tube by hand.
Pineapple (Ananti~ co99zos~~s>. which is planted using
crown cut from the tops of fruits, is planted in a fashion similar
to that for sugarcane.
Potato (Sola9zum
tuhc~osum) is propagated by planting
small whole tubers or pieces of tubers each weighing 40-60
g. Each piece must contain at least one eye. Potato can also
be planted from botanical seed-often referred to as ttzle
seed-but this method is used only for breeding work or in
specific situations where it is not feasible to store tubers for
seed. When botanical seed is used, the seed is usually planted
in a nursery and the seedling transplanted in the field.
Tractor-drawn potato planters are usually two- or fourrow units of either a trailing type or 3 seniinmunted 1ypc’
attached to the 3-point hitch of a tractor.
Potatoes are planted at a rate of approximately 1,500 kg/
ha, so large seed hoppers are essential. A typical 4row potam
planter, as shown in Figure 5.17, weighs 6 t when the hoppers
are filled with 11500kg of potato and 2.000 kg of granular
fertilizer. Potatoes are nomrally planted at 9O-~1~1 (36in) row
spacing. Seedspacing in the row varies from region to region:
%O-cm(s-in? spacing is common. but planters can be adjusted
to provide a seed spacing of IO-50 cm.
Besides the frame and the potato and fertilizer hoppers,
the important elements of a potato planter are the driving
wheels. planting mechanism, and furrow openers. The
driving wheels not only carry most of the weight of the
planter, but drive the planting mechanism. The furrow is
usually made by one pair of discs, while another pair covers
the seed piece. The planting mechanism must select one seed
piece from the seed hopper and drop it into a tube, which
direct,s it to the furrow. There is one planting mechanism I;)r
each row.
Two types of potato seeding devices are used as planting
mechanisms. The more common device is the picker pin
mechanism (Fig. 5.18). This is a vertical wheel with six to eight
picker pins attached to the circumference of the wheel. I&h
pin on the wheel j:ihs and holds a seed piece as it sweeps
5.17. A 4-row potato planter,
5.18. Potato planter using
picker pins.
through a t.rough. At a discharge point above the seed chute,
a cam-actuated finger pushes the seed piece from the pin. The
seed chute directs the seed piece to the furrow.
Seed cups are also used as a seed-metering device (Fig.
5.19). Seed cups are attached to a chain driven by one of the
driving wheels. Seed pieces fall into the cups as they sweep
past the bottom of the seed hopper. Excess seed pieces are
shaken from the cups. At a point above the seed chute, the
chain goes around a sprocket, and the seed piece falls from
the cup. The seed cup mechanism is usually preferred when
planting whole tubers.
Planting tests using cut seed at 8.6 km/h in level loamy
sand, with the planter set at a spacing’ of 46 cm. revealed that
the picker pin machine had an average spacing of 46.5 cm for
single seeds with a coefficient of variation of 31%. The seed
cup machine obtained an average spacing of 45 cm with a
coefficient: of variation of 360~&.~
The planter with the picker
pin mechdnism had better uniformity of seed placement: 82%
of the placements contained a single seed piece, 8% contained
doubles, and 10% no seed.’ The planter with the cup-type
mechanism placed a single seed piece in 72% of the placements, doubles in 23%, and no seed in 5%.
5.19. Potato planter using
seed cups.
5.4 Tools for planting
There are two major groups of transplanters: those used to
plant vegetable plants in upland soi!s and those used to plant
rice seedlings in wetland fields.
A transplanter for vegetables is essentially a cart carrying
the plants, with a furrow opener, a water tank, and so&firming
wheels. Most vegetable transplanters are two-row machines
with two operators, since one person is needed to feed the
plants into the mechanism for each row.
The operator selects a plant and places it into a pocket
attached to a conveyor chain. This transports the plant to the
furrow made by the furrow opener. Plant pockets are
attached to a wheel on some transplafiters. The plants are
placed i:: the pockets at the top of the wheel’s rotation; springloaded rubber grips hotd the plant; and a cam-actuated device
opens the grips and drops the plant into the furrow at the
bottom of the wheel’s rotation. The cam that actuates the
gripping device also opens the water valve so that water flows
into the furrow. The firming wheels firm the soil around the
plant as well as power the transplanter’s drive mechanism.
Most rice transplanting throughout the world is done by
hand. In industrialized countries such asJapan and Taiwan,
however, mechanical transplanters are used. For a mechanical rice transplanter to perform well, the field should be level
and puddled to a soil consistency that will hold the plants.
Unlike mechanical transplanters, humans doing manual transplanting are able to make allowances for irregularities in the
Production of rice seedlings is a very important part of
transplanting. More care is required in producing the
seedlings for machine transplanting than for manual transplanting, since the seedlings must be of a specific density and
height for placement in trays suitable for the transplanter. A
studyin the Philippines revealed that preparation of seedlings
for transplanting into 1 ha of wetland field required 23.2 manhours for hand transplanting, 46 man-hours for manual
machine transplanting, and 35.8 man-hours for power machine transplanting.”
In hand transplanting, the farmer spaces the seedlings on
a 20- x 20-cm grid. A line marker resembling a rake with 20
teeth set on 20-cm centers is pulled across the field to mark
the rows. The farmer plants the seedlings at a 20-cm spacing
in the row. In a well-prepared field? water depth during
transplanting is about 1 cm.
A typical manual transplanter is made of wood and steel
and is pulled by the farmer. The machine shown in Figure
5.20 transplants six seedlings simultaneously and has a
transplanting arm, six grasping forks, a wooden float board,
and a seedling tray. Seedlings are arranged in layers with the
stems parallel and the roots in contact with the surface of the
5.20. Manual rice
tray. A wooden plank presses the seedlings downward and
maintains their positions as they are removed from the tray
during planting. The transplanting arm is part of a bar linkage
on which six pairs of seedling pickers are mounted at equally
spaced intervals. As the transplanting arm moves up and
down, the bar pushes a swing arm. The swing arm actuates
a paw1 and movable ratchet, which slides the seedling tray
laterally to assure that seedlings are taken uniformly from all
parts of the tray. Two people work with the machine; one
arranges seedlings in the tray while the other operates the
To actuate the machine, the farmer pulls the transplanter
handle backward to its maximu!,n limit. This action opens the
seedling pickers. Next, as the handle is pushed downward
through the feeding frame slots, each pair of picker fingers
takes a small cluster of seedlings. The picker fingers continue
down into the soil to a depth of 2-3 cm. The seedlings are
released from the picker fingers by pulling the handle
upward. The farmer then steps backward one row and
repeats the same movement.
A 6-row manual transplanter is about 1.25 m wide, 90 cm
long, and 65 cm high. It weighs about 20 kg empty; it requires
a draft of 7-11 kg (69-108 N, 15-25 lb) when the field is
flooded, and lo-13 kg (98-128 N, 22-30 lb) when it is dry.
Travel speed depends on the fanner’s stamina, but is usually
about 0.6 km/h.
Most engine-powered rice transplanters are pedestrian
units. Some larger units are designed for mounting to the
three-point hitch of a farm tractor. These units carry an
operator to assist with the trays of seedlings. Planting depth
and distance between plants can be adjusted. The transplanter has a 3-hp, 4-cycle gasoline engine and is controlled by the
operator walking behind the machine. It consists of transport,
feeding, and planting components, as well as the engine. The
transport-propulsion coniponent is equipped with two steel
wheels and a plastic float. It is attached to the body through
a linkage mechanism. Seedlings are placed on an inclined
aluminum tray and gravity-fed to the planting forks. The
seedling tray moves reciprocally from side to side to assure
that a uniform quantity of seedlings is picked up by the
planting fork during each stroke.
The planting fork removes seedlings from the seedling
board in small clusters. A cam inside the planting mechanism
energizes the fork to grasp and hold the seedling cluster as the
fork traverses the seedling tray. The fork releases the cluster
in an upright position into the soil.
A typical power transplanter has a 3-hp gasoline engine,
It is 200 cm long, 90 cm wide, and 90 cm high, and weighs 80
kg. The transplanter plants 2 rows at 30-cm row spacing. The
operator guides the transplanter by a pair of handles as he
walks behind it. Working speed is about 2 km/h.
Table 5.1 compares methods of transplanting rice.
Table 5.1 Comparison of rice transplanting methods.9
transplanting transplanter
Time for seedling
preparation (h/ha)
Time to transplant (h/ha)
80-l 60
Total time (h/ha)
Row spacing (cm)
Seedling space in row (cm)
Missing hills (%)
Floating hills (%)
Planting depth (cm)
Plant population (no./mz)
Estimated grain yield (t/ha)
1. Steensherg A (.1971) Drill-sowing and threshing in Southern India
compared with sowing practices in other parts of Asia. Tof$s Tillage
2. Shein T (1988) E+abtion of different metering devices for multi-crop
seeding. MS thesis, University of the Philippines at Los Barbs, Laguna,
Philippines. 80 p.
3. De Vries C A i197X) New developments in production and urilization of
Alxt. Trop. Agric. 4:X9.
4. Branch D S. ed. (197X) Tools for homesteaders, gardeners and small scale
farmers. Rodale Press. 233 p,
5. Odigboh E V (1978I A two-row automatic cassava cuttings planter:
development. design and prototype ccxxtruction. J. Agric. Eng. Kes. 23:2.
6. Prairie AgriCUhUGIk
lnstirute (1978) Evahiation report no. El077
on the McConnell model 555 @ato planter. Humboldt, ~dSkatChewm.
7. Prairie Agricultural Machinery Institute (1979) Evaluation report no. E0579
on the Acme 4OOSTpotato planter. Humboldt. Saskatchewan,
8. Kim K U (1977) Field tests on three transplanting systems. Paper No. 7707. AgricuIturaI Engineering Department, International Rice Research
Institute, P.O. Box 933, Manila, Philippines.
9. Ibid., p. 17-19.
Evers E (1956) R&&at de I’enquete sur Ies machettes. Bull. Inf. INEAC,
Sommaire 5(l).
Tanaka K (1983) Transition from shifting cultivation to Iowkind wet-rice
cultivation--changes in conventional farm tools. Studies on the conventional farming tools and the evolution of farming systems in Southwest Asia.
Fa$ty of Agriculture, Mie University, Tus, Japan.
Campbell J K (1970) Development of a machine to pelletize small seeds,
Paper No. NA70-201. American Society of Agricultural Engineers, Newark,
The dispersal of animal nlanure on cropland serves two
purposes. First, it is a means for disposing of the manure gen,erated by animals kept in confinement. Second, manure is
valuable as a fertilizer because it contains elements required
for plant growth.
In nonmechanized agricultural systems,where both herders and farmers live side by side, a symbiotic relationship often
develops in which the herders graze their cattle on crop
stubble. The herder thus receives forage for his cattle, while
the Fdrmerreceives fertilizer. An example of this relationship
exists in Nigeria between Fulani herders and farmers from
other tribes.
In Ethiopia, dry cow dung is taken to fields coming out of
fallow, where it is mixed with dry turf to form piles about 1
m in diameter and 0.5 m high. The mixture is then burned,
and the ashes are scattered over the field. This practice
provides a flush of growth during the first cropping season.
Cow dung is also formed into cakes and burned as fuel a common practice in India and Nepal. A more beneficial use
of the dung requires capital investment. First, the animal
manure is put into a methane digester. The resultant biogas
can be used as fuel for cooking and light. Second, the fields
are fertilized with the manure efiluent. Not only does the
methane digester allow the farmer to utilize animal manure for
fuel and fertilizer, but the process prevents the production of
disagreeable odors.
Means of applying both animal and chemical fertilizers are
discussed in this chapter.
6.1 Rate of manure
production by animals
When manure consists of dry matter of 12% wb or less, it is
called liquid manure. When the dry matter is 16% or more,
it is called semisolid. Manure that is only 12-16% dry matter
is often difficult to handle by mechanization, since it is too
viscous for liquid manure handling equipment and too fluid
for semisolid manure handling equipment.
In many types of animal husbandry, straw, woodchips,
sawdust, and maize stover are used for bedding. A water i-lush
system is sometimes utilized for manure removal in dairy
Darnswhere the temperature does not fall below freezing for
extended periods. The amount of manure that must be spread
on the fields usually exceeds the amount of feces acd urine
the animals produce. In nonliquid manure systems, bedding
absorbs urine and thus captures nutrients that would otherwise be lost.
The amount and composition of animal feces vary with
the animal and the amount and composition of the feed.
Table 6.1 shows manure production without litter or bedding
for some common domest,ic animals.
Table 6.2 gives the storage requirements in the northeastern United States(temperate climate) for a clairy cow weighing 1350 lb (613 kg).
6.2 Hand tools for
Human excreta (night soil) has been used as fertilizer in the
Orient for more than 30 centuries. Night soil is stored in
stoneware or concrete-lined pits, and carried to the field in
pails attached to carrying poles or in barrels. It is then applied
with a ladle made of a bowl of galvanized sheet steel with a
bamboo handle about 2 m long. The ladle weighs about 1 kg
and holds 4-5 liters. It is light and inexpensive, but needs to
be repaired after 2-3 mo.
A water-carrying bamboo tube is sometimes used in place
ofa bucket and ladle to distribute night soil (Fig, 6.1).’ The tube
is about 13 cm in diameter and 80 cm long. It weighs ;Ibut
applying mamwe
Table 6.1. Manure production per 500 kg of animal liveweight.
Raw waste (kg/d)
Feces:urine ratio
Density (kg/ma)
41 .o
Laying hen
Table 6.2. Storage requirements for manure of a dairy cow weighing 1366 lb (613 kg).
Storage/cow per d
Form to be stored
Semisolid, under roof
Semisolid, in nonroofed building
Liquid, in open-top tank
Liquid, in earthen lagoon
1 kg and holds about 13 liters. Two tubes are carried on
a carrying pole. The night soil is distributed by pouring
from the end of the tube. A night soil tube has a service life
of about 1 yr.
6.3 Machines for
spreading manure
6.1. Night soil tube.
In a mechanized system, manure spreaders are used for
transportation and distribution. The mechanical manure
spreader, a wagon with a mechanical means to distribute
manure, was invented about 1l865.~ The unloading and
distributing mechanisms of small manure spreaders are
powered by the rear wheels. Large manure spreaders are
usually powered by the tractor’s PTO. Manure spreaders
are grouped into three types: box, flail, and closed-tank
6’J.Z Bo~s~re~~&vs.The box-type manure spreader (Fig. 6.2)
is used for manure containing enough bedding to be piled in
a heap. Small box spreaders are driven by the rear wheels.
For this reason the drive tires are mounted backwards relative to the drive tires on a tractor. On a ground-driven manure
spreader, the V of the tire’s tread points rearward instead of
forward. Animal-drawn spreaders are four-wheeled units.
Tractor-drawn spreaders are usually of a two-wheel trailer
A conveying chain at the bottom of the spreader’s box
moves the manure to the beaters. Box-type manure spreaders that unload at the front have been manufactured, but these
machines have not been generally accepted. Today, box-type
manure spreaders are unloaded at the rear. From one to t.hree
beaters are used to distribute the manure. In the three-beater
6.2. Box-type manure
system, two opposed action cylinders--usually with spike
teeth-tear and shred the manure. The cylinders throw
shredded manure onto the widespread beater, which flings it
rearward and to the sides to make an even swath about 6 m
wide. The three beaters are most useful when spreading
caked manure or manure containing a high proportion of
bedding. When manure contains less bedding and is spread
daily, a single widespread beater is sufficient.
A few PTO-powered box manure spreaders use powered
swinging flails-similar to those of a rotary tillage machine.
The unit distributes the manure evenly but does not make as
wide a swath as a three-beater spreader.
When using a box spreader to haul and distribute semisolid manure, a solid endgate is put in front of the beaters so
the manure will not ooze out under them during transport.
While spreading manure. the endgate is raised to allow the
manure to contact the beaters.
The ASAE allows two methods of calculating volume for
manure spreaders. The kwuped load methd assumes tllat
manure can be heaped up to 38 cm above the topmc;,,t beater.
63. Volumetric capacity oi
box-type manure spreaders.
This is possible only if the manure contains a good deal of
bedding such as straw. The struck &!e/ methou’of calculating volume is more realistic. It is simply the volumetric
capacity of the box while the heaped load is volume A + B of
Figure 6.3.
Ground-driven box spreaders range from 2.5 to 3.5 rn’ (7~
100 bushelsi heaped-load volume. PTO-powered box
spreaders range up to 17.5 m3. The larger PTO-powered
spreaders either have dual axles to obtain sufficient flotation
or are truck-mounted.
A small PTO box-type spreader requires an average of lo14 PTO hp for the unloading cycle, but there may be peaks
as high as 45 hp at the initiation of unloading. A large (12.5:n’) PTO box spreader requires an average of 15-20 hp for the
unloading cycle.
Some box manure spreaders use a pushing board or
piston instead of a slatted chain conveyor to move the manure
rearward. A winch and cable or a hydraulic cylinder may be
used to move the pushing board.
‘::i:;:;:;&$ /+ $g$g$:
63.2 Flail spreaders. Manure with little bedding (semisolid)
is easily transported and spread wit,h a flail spreader. All flail
spreaders are powered by the tractor’s PTO. The design is
simple. The flail spreader consists of a cylindrical tank with
a powered shaft along the horizont,al centerline of the
cylinder, as illustrated in Figure 6.4. CLains fastened to the
shaft fling the Imanure out from an opening in the side.
A flail spreader requires more power than a box-type
spreader of identical capacity. Flail spreaders from 5 to 12 mi
capacity require an average of 15-47 hp for the unloading
cycle, with peaks of 60-80 hp.
6.4. Flail-type manure
6.53 Closed-tmk sp-pr-eaders.Liquid r,:anure is usually transported and spread from closed-tank manure spreaders. These
spreaders are essentiaiiy t~r.!:s---usually cylindrical, but
sometimes rectangular-that are pumped full of tiquid manure. The manure is discharged through a nozzle by gravity,
air pressure, or pumps for a lo-12 m swath. Alternately, it can
be discharged through injection shoes. The volume of closed
tank spreaders is the internal volume in liters or U.S. gallons
(ASAE Standard 5326).
Liquid spreaders range from 3,000 to 20,000 liters capacity. Large tires are required for flotation because of the weight,
and a large tractor is required to control the unit on irregular
terrain. For example, an 8,000-liter (2,100-U.S. gal) spreader
weighs 8 t when loaded.
6.4 Machines for
applying chemical
Nitrogen, phosphorus, and potassium (N, P, and K) are the
principal fertilizing elements. Other elements such .as zinc,
boron, and molybdenum are sometimes required in small
amounts and are referred to as trace or micro elements.
Nitrogen, phosphorus, and potassium are found in animal
manure and organic fertilizers. Chemical fertilizers containing purer, concentrated forms of N, P, and K are man&ctured
in factories, although most K in the form of potash (K,O) is
mined from natural deposits. The weight of each of the major
ingredients of a commercial fertilizer is described by the
percentage by weight of N, P (P20i), or K (K,O) in the
fertilizer. For example, an 80-lb bag of 5-10-10 fertilizer
contains 4 lb (5%) of N, 8 lb (10%) of P,O,, and 8 lb (10%) of
K,O; the remainder is inert material.
Lime is not a fertilizer but is often added to the soil to
lower soil acidity (increase soil pH1, creating more favorable
growing conditions for plants such as maize and alfalfa.
Likewise, sulfur is added to the soil to increase acidity for
crops such as blueberries.
Throughout the world, N, P, K, and acidity ameliorants
such as lime are applied in the form of dry pulverized rock,
crystals, or uniformly shaped spheroids called prills. Anhydrous ammonia (NH,) is 82% N but is gaseous’at normal
temperature and atmospheric pressure. In countries where
NH, is inexpensive, however, it is injected into the soil as a
pressurized liquid.
Liquid fertilizers, in which the elements are dissolved in
water, are easy to formulate for specific applications. They
lend themselves to precise metering and easy handling by
pumps. Large voluines of water must be transported,
however. In application systems where it is advisable to
reduce the amount of water to be transported, fertilizing
elements are suspended in water and mixed during transport
to the field. These liquid fertilizers are called suspensions.
Irrigation systems are sometimes equipped to place
chemical fertilizer into solution and distribute the solut:ion in
the irrigation water.
The simplest method of applying dry
fertilizer is by carrying a container of fertilizer in one hand and
broadcasting it with the other. This is the most common
method of applying chemical fertilizer to the ricefields of Asia.
For upland row crops, fertilizer is dribbled by hand alongside
the rows.
Hand application has an advantage in that it requires no
investment for equipment; however, there are several drawbacks. The fertilizq cannot be applied with precision, nor is
it placed in the root zone of the plants, where it would be
utilized most efficiently. There is a health danger for the
applicator in that concentrated nitrogen fertilizers such as
urea can be absorbed through the hands, displacing oxygen
in the blood with nitrogen, causing the applicator to become
faint and disoriented, and to breathe 1,aboriously. If one is
broadcasting chemical fertilizer by hand. a hand scoop should
be used.
A manually operated seed fiddle or cyclone seeder in
which the fertiiizer drops onto a spinning disc that distributes
it by centrifugal force about 200’ to the sides and in front of
the operator does a satisfactory job of broadcasting granular
fertilizer on small fields. For lawns and smooth gardens, the
push-type spinner fertilizer distributor does the same job.
Unfortunately, many pieces of lawn and garden equipment
have such small wheels th;at they are difficult to push or pull,
and they often tip over when used on rough ground.
In ricefields, about 70% of the nitrogen fertilizer (urea)
broadcast onto the water is lost before it gets into the plant.
By placing urea in the root zone, 5 cm below the soil surface,
it is possible to reduce the loss to 40%. Urea is difficult to meter
in humid climates, since it absorbs moisture and tends to form
A manually powered push-type fertilizer applicator (Fig.
6.5) utilizes both an auger and a plunger to inject urea 5 cm
deep into the flooded ricefield. The machine must be used
on level fields with no deep water. .4lthough tests reveal that
the machine provides a 40% increase in fertilizer efficiency,3
it has not been widely accepted by farmers in Southeast Asia;
the price of the machine plus an application time greater than
that of hand broadcasting have prevented most farmers there
from using fertilizer injectors, although the machines utilize
fertilizer more efficiently than does hand broadcasting.
Because fertilizer is corrosive, hoppers, metering mechanisms, and chutes must be made of anticorrosive materials
such as plastics, rubber, stainless steel, or fiberglass.
Fertilizer is quite often applied 5 cm to the side of the plant
row and also 5 cm below the surface when planting seeds
such as maize in rows. The fertilizer attachments for animaland tractor-drawn planters are usually powered by a grounddriven wheel. Dry commercial fertilizer is applied by chainand-sprocket combinations for the metering drive, by adjustable orifice openings, or by both. A good fertilizer distributor
6.5. Plunger-auger fertilizer
Gross weight
Machine length
Machine width
Fertilizer capacity
Aoplication rate
Work rate
Labor requirement
Swath width
Plant row spacing
Injection depth
Maximum water depth
Application time
1 person
4 kg urea
50 to 200 kg/ha
0.5 ha/d
16 labor-h/ha
15-22.5 cm
4-5 cm
0.5-5 cm
l-4 wk after transplanting
should be able to provide uniform distribution at rates of lOO2000 kg/ha.
Most commercial fertilizer is applied by broadcasting.
Animal-drawn, ground-driven, or tractor-mounted, PTOdriven spinner-type applicators are simple and inexpensive.
They can provide even coverage if care is taken not to overlap
adjacent swaths. One-spinner units are more common than
two-spinner units (Fig. 6.6).
The simple drill-type box spreader, in which an agitat~or
at the bottom of the hopper moves granular fertilizer through
adjustable holes, provides even application. Its main disadvantage is that it is restricted to widths of 1.8-3.5 m (6-12 ft)
because of gates and highway regulations.
Pne;unatic fertilizer distributors provide wider swaths for
dry fertilizer-up to lo-12 m. The fertilizer is metered from
a central hopper into flexible tubes. A fan blows the fertilizer
toward deflection plates (nozzles), which distribute the
fertilizer. The advantages of pneumatic distributors are that
they provide the metering accuracy
of the drill-type
distributor, the swath width of the spinner-type distributor,
and narrow transport width. Disadvantages include the
expense of increased power and the need for a more complex
Grain drills and maize planters usually have options for a
fertilizer applicator so that planting and fertilization can be
combined (Fig. 6.7). When only a srmll amount of commercial fertilizer needs to be applied, the drill or planter with a
fertilizer applicator is a time saver. if large ;lillOLlntS
6.6. Spinner-type fertilizer
fertilizer are needed, however, it may be better to apply
fertilizer in a separate operation so that the time for planting
is not extended.
6.7. Drill-type fertilizer
64.2 ~Liquidf&ilizw.
Liquid fertilizer is easily handled
mechanically by pumps or gEiVity, and the rate of application
can be accurately controlled by nozzles and valves. Liquid
fertilizers are classified into two group,- -high pressure liquids such as anhydrous ammonia (NH,), and low pressure
liquids such as aqua-ammonia and mixed liquid fertilizer.
Ammonia is 82% nitrogen. It is a gas at normal temperature (its boiling point is -181 “C at sea level). It is stored as a
liquid by pressurizing it at about 1,725 kPa (250 psi). The
vapor pressure of the gas above the liquid in the thankis
utilized to force the liquid NH, through the metering gauge
and the applicator knives. As the pressure on the liquid NH,
is reduced to atmospheric, it flashes into gas and is injected
under the soil. Figure 6.8 shows a tractor-I?1(~UlltedNH,
Ammonia is attracted to water. so as long as there is some
moisture in the soil at the point of injection, the NH, will cling
to the soil moisture. Its affinity for moisture makes NH,
dangerous if not handled carefully. Ammonia equipment such
6.8. Tractor-mounted
anhydrbus ammonia applicator.
astanks, gauges, hoses, and applicator knives must be in good
condition. Operators should wea,r proper safety goggles and
have wash water available in case of a spill. In spite of its
iiabilities, NH, is an inexpensive form of nitrogen fertilizer in
many countries, because it is easy to apply. By dissolving a
nitrogen source such as NH, or urea in water, a solution
containing 20-25% nitrogen is obtained. The maximum
amount of NH, that can be dissolved in the water depends on
‘temperature. Aqua-ammonia has an advantage in that it is less
hazardous than NH,, and it requires simpler equipment. Like
dry fertilizers, where 2/3 of the weight is inert material, 3/4 of
the weight of aqua-ammonia is water. Aqua-ammonia can be
metered by a ground-driven peristaltic pump.” Figure 6.9
shows an aqua-ammonia injector for wetland rice.
In applying nitrogen fertilizer to the root zone of wetland
rice, pumps using aqua-ammonia have an advantage over mechanical injectors applying dry urea, since the injection tube
of the peristaltic pump machine does not get clogged with
soil. Also? the physical characteristics of the solution do not
vary like urea, which has a proclivity to absorb moisture. A
further advantage is that only the noncorrosive plastic tube of
the peristaltic pump contacts the aqua-ammonia.
When applying urea or aqua-ammonia to the root zone of
rice plants in a flooded ricefield, it is essential that the fertilizer
not be exposed to floodwater. It must be sealed into the soil
by a layer of soil between the standing water and the injected
fertilizer. If the urea or aqua-ammonia is exposed to the
floodwater, much fertilizer is wasted in the water. The injector
shown in Figure 6.9 has fins on the bottom of the skids to
“seal” the aqua-ammonia into the mud so that it is not diluted
by the irrigation water.
6.9. Gfanual, ground-driven,
4-row aqua-ammonia
injector for wetland rice.
7 Weed control
A weed is an unwanted plant in a farmer’s field. One farmefs
crop may be another farmer’s weeds. Weeds take nut:rients,
water, and sunlight away from the crop ant1sometimes make
it impossible to grow the crop. 7bis ch3pter discusses
mechanical ancl chemical means of ridding a field of weecls.
Since some of the machines for applying chemical herbicitles
are the same as those for applying insecticicles, some of the
tools and machines clescribed in this chaprer are also useful
for insect control, described in Chapter 8, and vice versa,
Weeding is one of the most important tasks of the small
farmer. Manual or mechanical weeding is most common, but
herbicicles are becoming increasingly availabie. IHandweeding requires little capital investment but a large amount of
labor, whereas chemical herbicides require a capital outlay
but little labor. The best weed control program combines
mechanical methods. chemicais, and crop rotation.
Wee& can be controlled in orcharcis ant1 tree plantations
by planting legumes as cover crops. In addition to suppressing weeds, legumes provicle soil nitrogen and forage for
animals. Hay, plastic, and sawdust mulches are used to
suppress weeds and retain soil moisture in some row crops
and small fruits such as blueberries ancf strawberries.
Cattle and sheep are useful in controlling weed growth in
and plantations of tree crops such as rubber,
coconut, and oil palm. Some farmers we geese to remove
grass from strawberry fielcls.
7.1 Mechanical weed
Mechanical weeding of upland crops removes the weeds from
the soil. Left in the sun, the weeds die of clesiccation. 111
wetland rice, most weecis can be killed hy pushing them
below the water to suffocate. Row-crop cultivation facilitates
hand weeding and is a necessity for animal- or tractor-drawn
mechanical weeders.
Some of the same tools used for weeding are used for
hilling (throwing soil up around plants such as potato and
maize). Hilling potatoes while cultivating prevents them from
protruding from the soil a.nd turning green. Hilling maize
smothers weeds within rows.
7.1.l Mama1 tools. The machete and the hoe are the most
common tools for weeding upland crops. Wetland rice
planted in rows is easily weeded with the push-type weeder.
If the rice is not planted in rows? hand pulling is necessary.
A person can hand weed only 0.1 ha of flooded rice a day.
The push-type rotary weeder illustrated in Figure 7.1 not only
eliminates the back-bending work of hand weeding, but
enables a worker to weed 50% more a day. The worker
pushes and pulls the implement back and forth between the
rows. A skid in front of the implement provides flotation in
soft soil. Weeds are uprooted and pushed underwater.
The cone-weeder, shown in Figure 7.2, uses a conventional weeder frame but has two conical rotors mounted in
tandem with opposite orientation. Smooth and serrated
7.1. Push-type rotary
weeder for wetland rice.
5 kg
1.2 m
Field capacity
20 cm
0.3 ha/d
7.2. Cono-weeder.
7.3. Push-type cultivator.
5-6 kg
1.4 m
Field capacity
37 cm
0.18 ha/d
blades mounted alternately on the rotors uproot and bury
weeds. Because the rotors create a back-and-forth movement
in the top 3 cm of soil, the cone-weeder can satisfactorily
weed in a single forward pass without a push-pull movement.
The sheet metal rotors are hollow to increase flotation, in soft
soil. Manual weeders are made in both one- and two-row
models, but two-row machines are rarely used.
For upland crops, the long-handled weeding hoe is the
universal weeding implement, although the same shorthandied hoes used for pnmary tillage are often used for
weeding in primitive areas. liesearch in Nigeria found that
with a long-handled hoe the spinal muscle force was only 20%
as great as when using a short-handled hoe, and the lumbosacral joint reaction only 38% as great. Thus a long-handled
hoe will reduce the backache of hoeing.’ Long-handled hoes
have two nlain variations: those that chop both weeds and
soil, and those that cut the weeds below the surface by a pushpull action. The former functions in all soils; the latter works
best in light, stone-free soils.
Manually powered push-type cultivators (large-wheel
hoes), such as in Figure 7.3, are most commonly used on
vegetable farms in loamy to light soils. The combination of
the large l&in (46 cm) wheel and adjustable handles allows
the operator to regulate work depth, while the frame, which
usually carries 5 shovels, can be variecl from about 10 to
15 in (25 to 40 cm> in width. A large wheel hoe weighs about
11 kg. The large wheel provides evenness of effort, since the
wheel rolis over small stones and uneven soil.
7..f.2 Animal- and tructor-powered machines. Weeding does
not require as much power as tillage, but it does require
control to assure that few weeds survive and that none of the
crop is destroyed. The cultivator, drawn by animals or
mounted on a tractor: is the most common weeding machine.
A between-the-row cultivating implement travels between t’,vo adjacent.rows. When drawn by a yoke of animals,
one animal is outside the right-hand row and the other is
outside the left-hand row. Ards (as shown in Figures 4.7-4.10)
set for shallow plowing are commonly used for removing
weeds from crops such as maize, bean, and potato. The
fanner must make several passesto completely cultivate the
area between the rows, but the technique does not require
expensive equipment. Moreover, ro-ws that are not quite
parallel can be weeded by maneuvering the ard without
harming the crop.
The five-tine lever-adjustable cultivator (Fig. 7.4) is a
superior implement for weeding using animal draft. These
cultivators normally have a land wheel in front to help control
depth. The hand lever facilitates adjustment for row widt~hs
of 60-106 cm (24-42 in).
7.4. Animal-drawn, 5-tine
between-row cultivator.
Worse-drawn, over-the-row cultivators (Fig. 7.5) are often
designed so the cultivator gangs can be moved right or left
relative to the wheels and main frame. This feature is
important when the rows are notequite parallel. In some units,
the movement of the gangs is accomplished from the
operatcir’s seat, which is linked. to the gangs. The operator
shifts his weight to the right and the cultivator gangs shift to
the right. Other models have a. stationary seat, and the
operator WCS ~CX p&z!:; tz :no\z thr Cga~z~. Opeidtorcontrolled cultivators that mount on the three-point hitch of
a farm tractor have a rigid frame and hitch, but the gangs are
connected to foot pedals so the operator can adjust for
crooked rows. The tractor driver I :lust drive carefully to avoid
ovenuorking the cultivator oper~dtor,
A tractor cultivator usu&iy has one gang for each side of
a row. A one-row cultivator as shown in Figure 2.7 has two
gangs; aqd an K-row cultivator, 16 gangs:, The soil-engaging
part of the gang differs depending on soil, crop, economics,
and farming practice. Gmgs are mounted on tool bars on the
front, sides, and rear of the tractor. The front and rear wheels
c:f the tractor and the cultivator gangs must be carefully
adjusted to fit the row width of the crop. For best performance
and ease of operarion, the cultivator should cover the same
number of rows as the planter used to plant the crop. For
example, a crop planted with a sir-ma, planter should be
7.5. Horse-drawn, over-therow cultivator with hoe
cultivated with a six-row cultivator. There is apt to be some
row width variation, but if the cultivator is set up for the same
number of rows as the planter and begins where the planter
began, the fartner’s work is considerably easier.
Shovels and sweeps on tractor cultivator? c,re similar to
those used on manual and animal-drawn c:lltivators. The
common cultivator shovel is 5 cm !Z in> wide, but shovels are
made up to widths of 9 cm (3 l/2 in>. Sweeps are set to run
nearly parallel to the soil surface. The outer wing tip of the
sweep should be only 5 mm above the sweep point. Sweeps
range in size from 15 to 60 cm (6-24 in>. Sweep size is the
maximum width of the sweep. Half sweeps run next to plant
rows. Shovels and sweeps are made of heat-treated highcarbon steel for durability. Figure 7.6 illustrates four elements
used with cultivators.
Trail-type rotary hoes consist of front and rear gangs set
in a common frame with spiders (hoe wheels) 15 cm (6 in)
apart. Each gang is mounted so that the spiders of the rear
7.6. Soil-engaging elements
of a typical cultivator.
Double shovel
Half sweep
Rotary spider
gang extend forward between the spiders of the front gang,
and the soil is worked every 7.6 cm (3 in). Trailing-type rotary
hoes are made in widths up to 7.3 m (24 ft). In crusty soil
restraining the emergence of seedlings, the rotary hoe is set
to penetrate 2.5-5 cm (l-2 in> into the soil; and field speed is
lo-15 km/h (6-9 mph) over the crop and in the same direction,
as the rows. The crust is pulverized, and many weed seedlings
are removed, but the crop seedlings are usually unharmed.
An adage advises, “When operating a rotary hoe, put the
tractor in high gear and don’t look back!” A rotary hoe can
be used to pulverize and pack the soil by pulling it backwards.
Rolling cultivators are similar to rotary hoes except that
rolling cultivators have twisted fingers (blades) that can move
the soil laterally as well as provide a slicing action. Rolling
cultivator gangs are made as right-hand xnd left-hand gangs
with two to six spiders per gang. Right-hand and left-hand
gangs are usually mounted as pairs. The gangs can be canted
in the horizontal plane to control the degree of cultivation and
lateral soil movement, and tilted to till the sloping side of a bed
as well as working on the flat. Rolling cultivator gangs are
norn~ally mounted on tool bars and are frequently used for
hilling crops such as potato as well as for weeding.
Cultivating row crops is not easy. Sitting on a horse-drawn
cultivator or driving a tractor demands clsse attention TOguide
the vehicle over the plants. Cultivation is monotonous, and
there is a tendency to doze until awakened with the shock that
the cultivator is off the row and removing the crop as well as
the weeds!
For a fallow field of grain stiltMe in a dryland farming
rotation, any growing plant is c~onsiderecl 2 weed. A rod
weeder is used to remove weeds without dist,urbing stubble
mulch. The rod weeder (Fig. 7.7) is visually ground-driven
and is made in both horse-drawn and tractor-drawn models.
The working element of a rod weeder is a ground-driven steel
bar, about 25 x 25 mm (1 x 1 in). The length is equal to the
width of the machine. The rod rotates in a direction opposite
to the wheels of the machine and is set to operate 5-10 cm (2
to 4 in) below the sdl surface. Plants struck by t,he rod are
pulled from the soil as :hey wrap around the rod. Herause t.he
rod rotates in a directicn opposite to the direction of travel,
uprooted plants are throii*!l from the rod to desiccate in the
7.7. Rodweeder.
The rod weeder is useful only in dryland fallow. In lush,
humid areas, the rod becomes clogged with vegetation.
Single units range in working widths from 2.5 to 3.6 m (8-12
ft) but may be ganged together to form widths of 11 III (36 ft).
7.2 Chemical weed
Pcsti&les are chemicals used to control pests. l~lerbicides
control weeds, insecticides control insects, and fungicides
control fungdi diseases. Pesticides are applied as gases,
solids, licluids, aerosols, or suspended solids.
Fumigation is the use of gaseous pesticides. It is used to
kill soilborne diseases and organisms. A gastight cover is
placed on the soil to be treated. and the fumigant is placed
under the cover. The gastight cover is usualb; a polyethylene
sheet laid over the soil with the edges lx~riccl t,c,seal in the gas.
Tractor-drawn machines unroll tht: *x~lyethylene sheet and
place earth over the sheet edges. Common fungicides such
as ni.ethyl bromide and chloropicrin (tear gas) are available in
pressurized cans for injecting the gas under the plastic. (Note
that methyl bromide can kill humans as well :IS soilborne
Steam is used as 3 soil fumigant. For example. in
fumigating soil for a tobacco seedling nursery, an airtight steel
cover 1.5 x 2.25 m and 12 cm deep is placed over the seedbcd
to be treated, and steam is piped through the ct;ver and into
the soil. Fumigation is expensive and is used only for highvalue crops and seedbeds.
Fire is a chemical reaction, so flame cultivation is included
in this section. Shifting agriculture utilizing :I slash-and-burn
(swidden) system uses fire to kill weeds, so crops such as
maize can germinate and obtain a head start on weeds. I-iandheld kerosene blamersresembling large blowtorches are used
in some areasto remove weeds from irrigation canals. In areas
where propane gas is inexpensive, flamers have been used to
control weeds in cotton. In successful flame cultivation, the
crop plant must be iarger and more heat resi-iant than the
weeds. A typical tractor-mounted flamer consists of a rear tool
bar with propane tank and flamers for four rows. Skids
positioned along each row control flame height. Burners with
tips 20 cm (8 in) wide are positioned on both sides of a row
so that flames are directed at 45’ to both sides of the row,
striking the ground about 5 cm from the plants.
Dusters mounted on tractors or trailed were formerly used
for applying pesticides to crops such as potato, and hand-held
units, manual or engine-powered, were used on ricefields. A
duster consists of a hopper for the dust, an agitator to prevent
caking and ensure free flow, a blower to provide air to
distribute the dust and to break it into fine particles, and a
spout or nozzle to control the direction. However, dusters
have been replaced in most field applicalions by sprayers,
since wind easily blows dust about, sometimes damaging
other crops; for best resu!ts dust shouid be appiied while
dew is on the plants. Dusts continue to be used in household
vegetable gardens, where the pesticide container serves as a
duster as the gardener shakes the container’s contents onto
the plants. Some pesticides. particularly fungicides for
greenhouse use. are sold as dusts. These are applied by handcarried manual or motor-powered blowers.
A simple means of applying a liquid pesticide is a handpushed rol/er ~~~,t&~~lt~~.A typical roller applicator consists
of a steel cylinder 50 cm in diameter and 40 cm wide. The
width depends on the width of the crop row. The unit’s other
components are a pipe to drip herbicide onto the roller. a
p&ic tank containing the herbicide. and a handle. When the
handle is placed on the ground, the drip pipe is above the
tank, thereby preventing liquid from flowing from the tank.
The roller applicator is advantageous in that t!lere is no
pesticide drift ont,o adjacent crops; the unit is simple to
manufacture (having no pumps or valves) and easy to use.
The primary disadvantage is that the applicator does not treat
all vegetation in a rough field. Weeds in soil depressions or
crevices may not come in contact with the roller.
The SV~Zsprayer is another wiping-action applicator. It
is used for wiping postemergence, trdn,ikxated
such as glyphosate on weeds extending above the crop
canopy or between crop rows. Contact with the top onequarter to one-half of actively growing plants is usually
sufficient for optimum control. The wick that transfers the
glyphosate solution from the reservoir to the weeds is usually
a nylon or polypropelene rope. Wick sprayers are made in
both hand-held and tractor-mounted units.
The wick sprayer is often impractical because the weeds
are below the crop canopy. In that case, the herbicide must
be delivered in droplets, either by field sprayers or by aerial
application. Optimum droplet size requires careful assessment. Small dropiets provide more coverage per weight of
solution. However. the smaller the droplet, the greater is the
risk of its being carried by the wind. Drift wastes herbicide
and can damage a nearby susceptible crop. Table 7.1 relates
droplet size to drift.
because droplets smaller than 100 p drift excessively, lowvolume sprayers commonly use droplet sizes of loo-250 p fol
cc?Xroiieci ciropiet appiicarion (CDAi. A rypicai pressure
sprayer with a flat spray tip. (*[email protected] 40 p:;i creates droplets
with a mean diameter of 500 pL.: In general, a coarsl: spray
consisting of large droplets is best for applying herbici&s, and
a fine spray of small droplets is best for fungicides and
which produce dro$ets smaller than 50 p,
nCJI’rKi~~y in the range of S-15 p, art discussed under chemical
pesJ control in Chapter 8.
Most agricultural sprayers create spray droplets by forcing
a liquid spray solution through a nozzle. The nozzle meters
the solution, atomizes the liquid into droplets, and disperses
the droplets onto the crop. Nozzles are crucial to the
Table7.1. Effect of droplet size on drift when falling 3 m in a 5 km/h wind.3
Droplet sizea
a 1 micron (p) = 0.000001 m = l/25.000 in.
I mi
2000 fr
(610 m)
( 15 m)
(1.5 m)
operation of a sprayer. Nozzles are normally made from brass,
nylon, or specially formulated plastic. Stainless steel, tungsten, and ceramic nozzle tips, however, wear better and are
preferred by commercial operators despite the higher initial
The hollow-cone nozzle produces a conical pattern, with
the droplets concentrated at the outer edge of the cone. It is
often recommended for good leaf coverage of field crops and
is also used to apply ixecticides. The flat-fan nozzle makes
an elliptical pattern used for applying fertilizers as well
as herbicides and insecticides. The nozzles are set on the
spray boom so that the tips of adjacent spray patterns overlap
to provide uniform coverage. The flood or wide-angle nozzle
provides a wider area of coverage for a specific height, but the
pattern may not be as uniform as that from a nozzle with a
smaller spray angle. Common hollow-cone and flat-fan spray
angles are 65” and 80”. The usual angle for flood nozzles is
120’. Figure 7.8 illustrates various nozzle spray patterns.
The nozzle on most manually operated, compressed-air
sprayers or knapsack sprayers is adjustable. By turning a
ferrule on the nozzle, the operator can change from a fine
spray to a coarse spray to a nearly solid stream.
A nozzle on a tractor-powered or self-propelled field
sprayer usually consists of a plastic body that attaches to Ihe
spray boom. A filter prevents the nozzle from clogging, a
spray tip provides the orifice required for the work, and a
pressure diaphragm prevents the spray solution in the boom
from dripping when the operator stops spraying.
Manually operated, compressed-air sprayers are portable
and useful for occasional pesticide applications. The units
normally hold from 5.5 to 9.5 liters of liquid pesticide
(concentrated liquid pesticide in a large volume of water). A
stirrup or pump-type handle pressures the sprayer. The
7.8. Nozzle spray patterns.
Hollow cone
,... ....,...,..
Flat fan
compressed-air sprayer cannot be filled completely with
liquid, because an air space at the top of the tank is necessary.
Otherwise, there would be no air to compress, and the energy
to force the liquid through the nozzle would be absent.
The knapsack or backpack sprayer--worn on the back
like a knapsack-is a nonpressurized sprayer with a piston
pump operated by nearly continuous hand pumping (Fig.
7.9). The pumping action forces the liquid spray solution into
a small surge chamber, which provides a continuous spray as
long as pumping continues.
The pump handle extends forward from the sprayer tank
so that the operator pumps the sprayer with one hand and
holds the spray wand with the other. The largest part of the
knapsack sprayer is the reservoir, which is made of brass,
stainless steel, plastic, or galvanized steel. Plastic units are
popular because they resist corrosion, are lightweight, and are
usually inexpensive. Also, the operator can see the liquid
level in a transkacent plastic reservoir.
The backpack power sprayer is engine-powered. A
typical backpack powe~r sprayer has a 20-liter (5.2-US gal)
tank, is powered by a 2-stroke air-cooled gasoline engine, and
weighs approximately 8 kg (18 lb) when empty.
7.9. Farmer using knapsack
In many countries, clean water is difficult to obtain. Large
volumes of water must therefore be carried to the field for use
with backpack sprayers. For example, to control brown
planthoppers in a ricefield, 190 liters of perthane/ha applied
at booting is enough. However, farmers are advised to apply
300-500 .liters/ha of a water and perthane solution. When
plants are small, the rate of 300 liters/ha is adequate, but when
the rice canopy is closed, the rate of 500 liter+ha must be
used. A farmer using a 204iter sprayer must apply 20
sprayerloads to 1 ha to obtain a rate of 400 liters/ha.
CDA sprayers are ligl- weight and produce uniform droplets. By comparison, ~~1the other sprayers mentioned
produce a range of droplet sizes, from larger to smaller than
A CDA sprayer forms droplets by running a small st~ream
of liqu:,cl spray solution onto a spinning toothed disc (Fig.
7.10). Dropiets are formed as they are flung from the teeth of
the disc. Droplet size is controlled by the viscosity of the spray
solution, the rate of flow of the solution onto the rotating disc,
the size of disc teeth, and the speed of the disc. The spinning
discs of most hand-held CDA sprayers are driven by electric
7.10. A hand-held controlled
droplet application (CDA)
Feed nozzle
Snap-on !xwer
7.11. Tractor-powered field
motors powered by ordinary flashlight batteries in the handle.
Flow of the spray solutjon from the reservoir to the disc is by
gravity. The application rate can be controlled by adjusting
the orifice between the reservoir and the spinning disc, by
walking speed, and by boom height. Application rate can also
be cont,rolled by adjusting the concentration of the spray
solution, but the advantage of the CDA sprayer is that it is a
hand-carried unit in which a concentra.tedspray can be used.
This is an important consideration in countries where clean
water is not readily available. For example, a CD.4 sprayer can
do a good job of weed control at a rate of 40 liters/ha, whereas
a convei?tional knapsack sprayer requires 200 liters/ha. A
disadvantage of ;he ultralow-volume sprayer is that it produces small eropleis that drift easily.
Whether animal-powered, ground-driven, or tractorpowered by the PTO (Fig. 7.11), a field sprayer must have a
tank, pump, pressure-relief valve, control valve, boom, and
nozzles. It should also have a pressure gauge, tank agitator,
and filter. Auxiliary devices such as hydraulically operated
spray booms, sonar control of boom height above the ground,
foam swath markers, radar &,Iputation of ground speed, and
computer-controlled spray rate are available. Besides these
auxiliary devices, there are many modifications for propelling
the spray into the foliage. Field sprayers with low-rate nozzles
and CDA applicators utilize fans to blast the small spray
droplets into the foliage, thereby reducing drift. Figure 7.12
illustmtes the elements of a typical field sprayer.
7.12. Elementsof a typical
field sprayer.
Pressure relief valve
Shul-dl valve
Flexible boss
Tillage implements such as a chain harrow, disc harrow,
or power harrow are as essential as the field sprayer when
applying some pre-incorporation herbicides to the seedbed
before planting. Some types of pre-incorporation herbicides
must be stirred into the top 5-10 cm (2-4 in) of the seedbed
immediately after spraying. For applying these herbicides, a
tractor pulling a harrow or a disc folhws the tractor and
sprayer. It is often necessary to go over lhe field twice with
the harrow or disc, the second passbeing perpendicular to the
firsi, to ensure incorporation of the herbicide. Some farmers
use one tractor by mounting the sprayer on the tractor and
pulling the harrow or disc. The sprayer is shut down for the
second pass.
Electrostatic sprayers are designed to cha,rge the spray
droplets so there is a powerful attraction between the plant
and the charged dropiets. A typical voltage is 25,000 V, but
the current is only about 3 pA. An electrostatic sprayer allows
the use of small droplets of 50 p or less, and the high velocity
of the droplers and their electrical charge, which makes them
mutually repellent, eliminate drift in most situations. Nearly
ali the spray reaches the plant, with both leaves and stems
receiving about even coverage. Practically no spray escapes
into the environment. An oil-based liquid formulation is
necessary, but the pesticide is supplied ready to use, so
measuring and mixing are unnecessary. However, electro-
static sprayers have not yet been accepted by most farmers
because of their high cost and operational problems.
A ground-driven fie!d sprayer manufactured in Paraguay
uses a diaphragm pump powered by a cam fixed to one wheel
of the sprayer. Roller vane pumps or centrifugal pumps are
the common pumps for PTO-powered field sprayers. Centrifugal and diaphragm pumps are commonly used for applying wettable powder mixtures because they withstand the
wear of the abrasive particles in those mixtures better than
roller or gear pumps.
Disposal of unused spray solution after spraying is a
iMany fanners spray the remaining solucommon pidAn.
tion on the crop--in effect applying more spray than is
required or lawful. Others dump the remainder. A propel
disposal site has a washdown area for the sprayer as well as
holding and evaporation basins for the unused spray solution.
None of these means of disposing of unused spray solution
is satisfactory.
Some spraye:s hold only water in the reservoir, and the
pesticide is injected into the water as it enters the boom. Thus,
after spraying, no spray solution remains to be disposed of.
As enviromnental concerns receive man’ attention and as
microprocessors become increasingly available for agricultural machinery, this type of sprayer wi:i gain :3cceptance.
1. Nwuha E I U, Kaul K N (‘1986) The effect of working posture on the
Nigerian hoe fanner. J. Agric. Eng. Ices. 33:179-185.
2. Spraying Systems Company (1984) TeeJrt Cavdkq 38. Wheaton, Illinois.
3. Kempen II (1978) Controlled droplet application-new
tool for your
growers. Agri-Fieidmdn and Consukdnt, Meister Publishing Co.. Ohio
Boise L M, Domhrowski N (1976) The atomization characteristics of a
spinning disc ultrd-low volume applicator. J. Agric. Eng. Kes. 21:87-99.
Diprose M F, Benson F A (19%) Electrical methods of killing plants. J, Agric.
Eng. ks. 30:197-209.
Fraser F, Burrill 1.(1979) Knapsack sprayers. International Plant Protection
Center, Corvallis, Oregon.
Millier W F (1987) How to apply pesticides accurately. Agriculturdl
Engineering Facts EF- 11. Cornell University, Ithaca, New York.
Insect an
predator c
This chapter primarily concerns insed control, hut Am covers
tools and techniques far controlling other pests such as
rodents md hit&.
One methocl of insect control that cloes not involve: tools
01 chm~icals is to ot>ser\Je the correct pI:ttjti!:g titny. tbt
example, the Hessem fly can br cotitrokcl in winter w~hcat
if the wheat is not planted until after ;I cert;tin ckttr.
Crop rotation is another itnportiint tne:tns of controlling
insects. Spwific insects thrive on specific crops. If the s:tmc
crop is gwvn year after year, an inueasing tilttnk
of insects
ackip! to feeding Or1it. Crop rotation can txeak fhc host j>lCii?!insect relationship atid recliicc the insrct population. Siniikirty, pests that li:we few alternative hosts an Ix i~c~~ntrollrcl
by removing the crop by ;t specific date. For e:ttnp!e, piId;
l~oilwwms in cotton can Ix controlled if the stalks ;irc
irprooteci xttl lxtrntrd when there are no dtwtxttivc host
The use off~en&ktl
insects or disc:iscs to control hartnl\tl
insects is called tklogid
cotitrd. For exrtiiplr, \vasps ;ifi‘
iisecl to control alf~tlfii weevi!s. anti cliwzw is ititroclii~ecf to
control Japanese f~)eetles. When tX>th t~iological control ant1
pesticides are used, pesticide application must 1-wtilwd so lhc
txxwficial insects wiil Ix unti;trnied. Another form of thio!ogicd control is growing plants ttiz! discourage pests. For
exxnplc. lemongrass is often gr-o\\x~ in g;irckns to tqwl
certain insects. and niririgolds ;tre planted in fielcls to ctiscuitrage netxttodes.
8.1 Mechanical
Kttic methods of insect control suctt ;is fine mesh scrc’cns art‘
commonly used in pktti: txeriiitig est:tl.)iist~itn~tits I-jut are too
expensive for ficlcl procluction. Eltdi-ic ki>CCS ;iW itistdkci tq
rice breeding institutes to kill rodents. Plastic netting protects
fruits such as blueberries from bird damage. The netting is
lightweight and is draped over the bushes when the berries
begin to ripen. After the berries are ripe, the netting is
removed, the berries are harvested, and the netting is rolled
up. In Southeast Asia, certain valuable varieties of tree fruits
are protected from bats by placing a rattan cage around each
The simplest mechanical method of removing insects
from crops is to pick them off manually. Where insecticides
are not available, children are often fielded to pick off hamtil
insects. During World War II, German schoolchildren picked
Colorado potato beetles to save the potato crop. Similarly,
home gardeners often pick Japanese beetles from crops.
In China. worm combs, worm scoops, and worn1 catchers
are used to remove wonns and stem borers from rice plants.’
Worm combs (Fig. 8.1) and worm catchers are used to comb
worms from the leaves of rice plants and drop them into the
water to drown. This work requires about 3 h/ha. A worm
scoop is a shallow bamboo basket on the end of a long handle.
The worms are caught as the scoop is swept across the leaves.
8.1. Worm comb.
Best results are obtained if the scoop is used after rain when
the worms are siuggish.
Tillage practices can also be used to reduce the insect
population. Research in China indicates that early spring
plowing can exterminate hibernating rice borer (Schoenohius
incertellus) and rice stem borers (Chile simplexk” In North
America, the maize borer can be controlled by clean fall
plowing in which all maize stalks are buried.
When birds are a problem-especially
near harvest
time-they can be frightened away by noise and slingshots.
Elaborate networks of string and cans radiating from a hut are
often used t:~ frighten away- birds. Automatic noise makers
powered b). propane or acetylene gas to produce loud
explosions are initiaily~successful, but, because of the regularity of explosions, soon lose their effectiveness. Kites and
scarecrows resembling owls are also effective until the birds
reaiizt! no threat exists.
8.2 Chemical control
8.2. Portable fogger.
Most oi’ the spraying equipment for weed control described
in Chapter 7 can also be used t.o apply insecticides. Foggers
or mist blowers using oil-based sprays are used to control
mosquitoes, fungi, and other pests.
The fogger shown in Figure 8.2 uses a Helmholtz resonator to produce a pulse jet by the same principle as the V-I buzz
bomb or a pulse jet furnace. C;asolineis burned in a resonator,
creating about 80 pulsations per second in the resonator pipe.
An oil-based liquid insecticide is introduced into the end of
the pipe, where it is converted to fine droplets and forced into
the air by the exhaust jet. A epical hand-carried model
weighs 9 kg and distributes 10-X iiters of pesticide per hour.
Small, hand-held, electrically operated foggers are commonly used in greenhouses. They are similar to household
humidifiers and produce very small (5-15 ~1 droplets by
vibration. A fan blows the droplets onto the plants.
Pesticides for soil-dwelling nematodes, and systemic
pesticides that are absorbed by the roots and translocated to
the stem and leaves to control sucking or biting insects are
usually applied in dry granular form during planting. The
application equipment for granular pesticides is similar to that
used for applying dry fertilizer.
Liquid systemic pesticide can be injected at the root zone
of rice plants in lowland cultivation with a peristaltic pump
injector similar to the one illustrated in Figure 6.9. Nitrogen
fertilizer can be injected between adjacent rows, and the roots
will eventually reach the fertilizer, but since the effect of a
pesticide is desired immediately, systemic pesticide must be
placed directly into the root mass of each plant.
Pheromone traps contain a chemical sex attractant to
capture specific insects. The traps are usually made of
inexpensive paper, plastic, or metal, and set above the canopy
of the crop to be protected. When using pheromone traps, it
is important that a sufficient number be placed in the field and
that they also be placed in adjacent fields planted with either
the same crop or with other host plants.
; :\I;; c &.:l~;~:honr,~
I.&-abaka 1. Yang Ching-wen (19581 A preliminary study
of farm impiemenb used in Taiwan Province. Plant Industry Series No. 4.
2d ed. Joint Commission on Rural Reconstruction, Taipei, Taiwan, China.
p. 158-163.
2. Huang C P, Lo S N, Shao H C (1957) Experiment in early spring plowing
in order to exterminate hibernating insects in rice fields [in Chinese]. East
China Sci. Agric. J. 1:42-44.
Gunkel W W, Campbell 0 F (1984’) A granular pesticide applicator for
blackbird control in growing corn. Staff Report No. X4-2. Department of
Agricultural Engineering. Cornell University, Ithaca, New York. 12 p,
Hughes H A (1082) Crop chemicals. Fundamentals of machine operation
series. 2d ed. Deere & Co., Moiine. Illinois. 20 p.
Huitink G (1980) Pattern your AG spray plane. Publication MP 183.
Arkansas Cooperative Extension Service, University of Arkansas, Littie Rock.
Arkansas. 12 p.
Thompson L jr., Skroch W A, Beasley E 0 (1981~1Pesticide incorporation,
distribution of dye by tiIIage implements. Publication AG-250. North
Carolina Agricultural Extension Service, North Carolina State University,
Raleigh, North Carolina. 32 p.
Y Harvesting
Harvesting is usu:~IIy the high point of the agricultural
calendar, for it is the time when the fruits of the farmer’s labor
are about to be realized Timeliness is essential; thus, a peak
work demand occurs at harvest time. Tools ancl machines are
usecl by most of the world’s farmers to alleviate the clernands
of much work in a lirnitecl time. The tools and nxachines usecl
in harVeSting grain, root, forage, nnd fiber crops are discusseci
in this chapter.
9.1 Grain harvesting
Because the rnethocl by which grain is harvestecl affects
sulxequent operations such as threshing, storage, and m&
ing, it must be selectect xvith care. Among the conciitions to
consider are evenness of ripening. type of field, wreck.
animal pests, labor, and economics.
The three phases of grain harvesting are reaping, threshing. and cleaning. The intervals ktt~xen these operations
vary greatly &pending on the harvesting method empkiyed.
It is of+ necessary, for example, to dry the grM after raping
to :ivoicl spoilage in smrage. Wheat, barley. rye, aid nuize
can be consunxxi by hu~nans after threshing. Rice, oats, ancl
some sorghiws must be liulleti before they can he consimecl
by humans. although they are usually store4 with hulls intact.
Grain must ripen before it c;tn be harvestecl. Many grains
such as wheat, oats. ryu, barley, and maize are usually
hxvested at a dry time of year. Rice, on the other hand, is
often harvest4 in fields where water+aturateci soil cannot
support the machinery useci to harvest grain oil dry land.
Hat-vest time is the most iqortmt
time of the agricultural
calendar. Until the grain is Iixvested and safely stored, the
farmer’s investment in tillage, se&, fertilizer, arlcl pest WIItrol
cannot be compensatecl. f:urtherniore. grain to feet1 the
family cannot be ohtainecl.
9. ,I. I Hand took;.The ani-ani is a specialized grain harvesting
tool used in Indonesia and southern Philippines to harvest
certain rice varieties (Fig. 9.1). It consists of a wooden peg set
through a thin, crescent-shaped piece of light wood carved to
fit the palm of the harvester. A thin steel blade, about 3 cm
long, is set into the wood. The farmer cuts one stalk of rice
at a time by using the index and second fingers to pull the rice
stalk across the blade to sever a short piece of stem and the
attached panicles from the plant. The severed stem is about
12 cm long and is held in the fingers until a bunch is collected.
The bunch-a miniature sheaf-is tied with a straw and later
sun-dried and threshed. The ani-ani came about because
native varieties of rice did not ripen uniformly and had to be
harvested as individual stems, Sickles are replacing the aniani as even-ripening, higher yielding varieties are increasingly
The sickle is the basic tool for manual harvesting of grains
and other cereals. Hand sickles have evolved into two general
types: serrated (Fig. 9.2) and smooth (Fig. 9.3). The serrated
edge is needed to cut tough and abrasive rice stalks. A typical
rice sickle is 25-30 cm long and has a curved steel blade and
a wooden handle. The farmer holds the rice stalks in the left
hand and cuts across the base of the stalks with the sickle in
the right hand (or vice versa if he is left-handed). One person
9.1. Ani-ani for harvesting
9.2. Serrated sickle.
9.3. Smooth sickle.
can harvest about 0.2 ha of rice per day. Sickles and knives
for harvesting rice and other grains vary from place to place.
The shape of a sickle often depencls on tradition as much as
The smooth sickle can be sharpened by hammering the
edge on an anvil or honing it with a whetstone. The serrated
sickle is more time-consuming to sharpen, since the work
mc!st be done with a small file.
The scythe is primarily a tool for mowing grass. When
fitted with a cradle to hold and bunch grain &vested by a
sweep of the scythe, it is an efficient ,tool for harvesting grain
such as wheat, rye, barley, and oats. The positions of the nibs
(hand holds) on the snath (handle) are adjustable and are
firred to accommodate the farmer’s height and arm length.
When using a scythe, the farmer takes a short step forward,
stops, pivots at the waist, and cuts the crop within the arc
described by the blade during the pivoting swing (Fig. 9.4).
If the scythe has a cradle, the fanner tips it at the end of the
swing, and leaves the grain stalks on the ground to be tied into
a sheaf later. Because of the design of the scythe and cradle?
grain is cut with a stubble height of about ‘IO-15cm (.4-Gin).
Since the scythe cuts grain close to the ground while the sickle
can be used to cut grain with a short st.em, the type of
threshing must be considered when selecting a sickle or a
scythe. If the grain is threshed by trampling on a threshing
floor, a short stem is desirable. Rice is threshed in some
Southeast Asia? areas by four or five people doing a slow,
dancelike shuffle in bare feet on top of dried bunches of rice
on a woven mat.
Flailing has long been used to thresh dry beans and
cereals such as wheat, rye, barley, rice, and oats. A stick can
9.4. Reaping with a scythe.
be useci as a &I to thresh these cereals. The crop is placed
on a mat or :I threshing floor. The threshet-s sit by the mat and
strike the crop with sticks until the grain is separated. Simple
sticks are inefficient. however, since the part that strikes th,e
grain should he paraliei :o the floor. A hand-held stick usually
strikes the crop at an angle.
A better tool is the flail, which consists of a working part
called a swingie and a handle called a staff The swirrgle is
a flat piece of wood al:out 5 cm wide ancl 7S cm long. It is
fixed to the staff by a flexible wocjden joint or a leather thong.
The staff is about 1.3 m long, depencting on the physique of
the user. The advantage of a flail over a stick is that, because
of the tlexible joint, the swingie strikes across the crop with
full force. Also, the farmer can work from a comfortable
stancling position (Fig. 9.5). In colonial America. 7 bushels
(lc)O kg) of wheat or 18 bushels (260 kg) of oats coulti be
threshed with a flail in a clay.
Ear maize icob maize) can be shelled (threshed) by
placing the ears in a large gunny sack and heating the sack
with a stout pole. The kernels are threshed from the cobs and
are not lost, since the entire process takes place in the sack.
The disadvantage of the technique is that some of the cobs are
9.5. Threshir,g with a flail.
broken and must be removed from the grain. Another method
of shelling maize is to build an elevated slatted floor. The
spaces between the slats should be larger than a maize kernel
but smaller than a cob. The maize is spread on the floor and
beaten *with a stout stick. The kernels fall through the spaces
between the slats and are collected brlow the platform. These
methods provide best results when the maize is very dry.
A simple hand-held sheller consisting of a truncated cone
with internal flutes can be used to she!! one ear of m&e ate
a time. The sheller is held with one hand, and the ear is twisted
in the sheller with the other. These shellers are inappropriate
for small farmers because of the considerable time required
to shell the maize. Moreover, in many countries no premium
is paid for shelled maize free of broken cobs. Hand shellers
are more appropriate for plant breeders and other experimenters who need small batches of clean seed maize. A
practical type of manually powered maize sheller is the twohole disc-ppe sheller (Fig. 9.6). This tool consists of a cast-
6.6. Manually powered
disc-type maize sheller.
iron disc with teeth on both sides. Chutes feed ears to both
sides of the disc. As the ears are constrained between the sides
of the machine and the rotating disc: the teeth rotate the ear
and remove the kernels. This type of sheller, which may be
motor-driven, does not break the cobs.~
In Asia, the primary method of threshing rice is beating
sheaves against threshing racks, logs, or rocks 3-10 times
depending on the variety. The grain fails. and the sheave of
straw is tossed aside. Since some rice flies off to the side, many
farmers recover the grain by placing the threshing rack in a tub
surround-d by sacking for about 300” and about a meter high
(Fig. 9.7).
Foot-powered treadle head-threshers with a wire l(~p
cylinder are used by farmers fo- comfort or for hard-to-thresh
rice varieties (Fig. 9.8). The operator holds the grain (head)
end of the sheave in the thresher. When the wirr? loops have
stripped out the grain, the sheave of straw is tossed aside.
Wire loop threshers are effective for rice, but not for other
grains (except perhaps oats>. Results of tests of the threshing
rack, the pedal thresher, and engine-driven threshers in the
Philippines are shown in Table 9.1.
In Bangladesh and Peru, efforts have been made to design
hand-cranked or foot-powered rasp bar threshers, but they
have been unsuccessful. Wheat is more difficult to thresh than
rice, and the power requirements for a hand-~cranked wheat
thresher have been too high for farmer acceptance.
Where grain is manually threshed, it is usLlally cleaned by
manual winnowing. The grain is poured in :I thin stream into
9.7. Rack in tub for threshing
9.8. Wire loop treadle
Table 9.1.Characteristics of threshing techniques in the Philippines.’
Threshing rack
Pedal wire-loop thresher
Motorized wire-loop thresher
Axial-flow thresher (about 7 hp)
McCormick thresher (about 40 hp)
(kg/man per h)
the wind so that the wind removes the light chaff and straw
pieces as the heavier grain falls into another basket or onto a
mat. Sometimes a hand-operated fanning mill is used to
create artificial wind.
91.2 Keqxrs. The reaper is a machine that cuts grain and
places it in a windrow, where it is gathered and bound into
sheavec and carried to a thresher. Large reapers-sometimes
called g;-:r!n windrowers-place
the grain in a windrow where
it is collected by a combine with a &nc!cow pickup.
The widths of cut for reapers for pedestrian tractors are
commonly 1, 1.2, and 1.6 m. These reapers are used primarily
for harvesting rice, although they perform well with other
grains. Grain stalks are cut with a scissor action between
a reciprocating sickle bar and ledger plates mounted on
9.9. Reaper on pedestrian
Power, brake hp
Weight of reaper
48 kg
Tractor + reaper weight 135 kg
Length, overall
2.2 m
Width, overall
1.2 m
Height, overall
90 cm
2-4.5 km/h
Forward speed
Field capacity
2.4 ha/d
Minimum stubble height 7cm
conventional mower guards. Star wheels and tv;o belts keep
the crop standing ltpright as it is moved to the right and
released to form a windrow. The reaper shown in Figure 9.9
is an attachment for a pedestrian tractor.
Animai-drawn reapers (Fig. 9.10) were developed from
the McCormick reaper, which was l~asically a mower with a
platform. A man walking behind the machine raked the grain
from the platform to form a windrow. Today, animal-drasvn
reapers often have ground-driven cam-rakes. The most
common type of animal-powered reaper has a moving canvas
platform behind the cutterbar that drops the grain from the
right side of the machine into a windrow. This reaper usually
hdS a grain reel that facilitates cutting a lodged crop. When
a tying mechanism is added, this type of reaper also ‘becomes
a binder (Fig. 9.11).
Animal-drawn reapers and binders are powered by ;1large
bull wheel, which carries most of the weight. By means of
gears, chains, and sprockets, the bull wheel powers the
sicklebar and the knotter. The knotter uses binder twine to
tie stems of grain together into shenves. The operator dumps
five to six sheaves by actuating a. foot trip tlrat releases the
bundle carrier.
In North America, workers waiking behind the binder
pick up two sheaves at a time. Standing the sheaves, upright
9.10. Reaper.
9.11. Grain binder.
with the grain on the top, they place four together and fan out
a fifth sheaf on top. This sheaf serves as a roof to protect the
sheaves from rain until they can be threshed. In areas where
rain is not anticipated at harvest. six sheaves are set together
with no Sheaf on top. In some localities in the Philippines
where rice is cut with a sickle and tied into sheaves by hand,
about 25 sheaves are placed rogether to form a shock. On
some farms the sheaves are hauled into a barn and threshed
several months later. In other localities the thresher is brought
to the field at harvest time and the sheaves are hauled from
the shock directly to the thresher.
Reapers ,:iounted on four-wheel faml tractors (Fig. 0.12)
or designed as self-propelled machines are used when grain
is endar.~_cxd by hail, when weeds in the grain must be dried
so that tht>y can be separated hy threshing, or when moisturesensitive crops such as birdsfoot trefoil seed are harvested.
Self-propelled reapers are also used when economic conditions preclude the cost of binder twine or combines, but a
machine of more capacity than a pedestrian tractor reaper is
Self-propelled windrowers utilize moving canvas platforms to move the grain stalks from the sicklebar to t,he
centerline of the machine, where the stalks are dropped into
a windrow.
Most tractor-mounted windrowers frxm the
windrow at the side of the machine instead of the center. It
is important when forming a windrow that the grain heads are
all in the same direction and the stalks are more or less
Schematic of a
.mounted reaper.
!2.1..3 ‘Th~shcrs. In sections of Indonesia rice is threshed by
men and women in IXIIY feet, shuffling in the form of a dance
upon sheaves of rice lying on a woven reed mat. Periodically,
the straw and grain are removed from the mat, and unthreshed
sheaves are added. Threshing rice by this means is possible
became the rice is I~~~:vest~dby an ani-ani (see Fig. 9.3 ) and
thus 1~~svery short stems. Fmthermore, the sheaves arc dried
in the sun for a number of days before threshing. Rice is easier
to thresh than most grainsI and dry sheaves of rice are very
easy to thresh.
Threshing by animal hooves on a hard clay floor is an
ancient agricultural practice. Bullocks, water buffalo, donkeys, and burros are the most common animals used for
threshing in this manner iFig. 9.13).
9.13. Bullocks tramping out
grain on threshing floor.
In using a threshing floor, sheaves of grain are laid out in
a low cone about 4 m in diameter and ranging from a height
of about 1.5 m at the center to a single layer of sheaves toward
the edge. As the animals tzmple out the grain along the
periphery of the circle, straw- is removed and more sheaves are
tossed under the animals’ hooves.
Farm tractors have replaced animals on threshing floors in
some countries. The tractor drives around and around the
threshing floor, with the lugs of the pneumatic tires threshing
cx:t the grain. The method of removing the straw from the
peripher)l and tossing unthreshed sheaves from the center
renlains the same. This is not an efficient use of tractor power.
but tractors purchased for tiltage or transport can be used for
threshing wit,h no modification of the traditional threshing
floor, except that it is no !onger necessary to scoop up animal
A study in Sri Lanka compared threshing rice on a
threshing floor by water buffalo. a farm tract,or, and a 5,-hp
mechanical thresher.? The sheaves of grain were piled 5 ft
(1.5 mj high in the center and out to a diameter of 12 ft (3.6
m). Five m-ater buffalo were driven around and around at a
speed of 2.25 mph (3.6 km/h) for the animal threshing test.
The tractor threshing was done by a 45lip farm tractor going
around and, around at a speed of 5-10 mph (B-17 km/h). The
thresher was 21s&l axial-flow
type, as shown in Figure 9.14,
powered by a 5-hp engine. Results of the study are shown in
Table 9.2.
Concrete and asphalt highways serve as long threshing
floors, and passing cars, trucks, and buses as the threshing
implements in many rural parts of the world. Sheaves of grain
lying on the highway are threshed as they are rubbed between
9.14. Small axial-flow
thresher with oscillating
cleaning screens.
Fower, brake hp
7 hp
Weight. with engine 190 kg
/ sor
305 mm diameter x
710 mm
Table 9.2. Comparison of threshing floor and mechanical thresher.
5 water bffalo
45-hp farm l:actor
5-hp axial-flow thresher
kg grain/h
Threshing Threshing
efficiency hours per im
of rough rice
?wJ:~per ton
of rough rice
Head rice Fuel in
(US gal/t)
6.2 5.0 (1.3)
3.5 (0.9)
the highway surface and the rubber tires of the vehicles. The
work is not strenuous and is often done by young children or
old persons. Not only do the tires of vehicles do the threshing,
but the draft of fast-moving vehicles also blows away much
of the ctiaff. This form cf threshing can be dangerous, slows
traffkc, damages grain, and in many countries, e.g., China, is
illegal. However, farmers without threshing equipment continue’the pra.ctice, since it is easier and faster than flailing the
grain out by hand. Local police do not enforce the ban on
highway threshing, since they too are part of the local
agricultural community.
The small mechanical thresher has the advantage that it
can be carried to the ricefield so that sheaves need not be
transported to the threshing area. The study reported in Table
9.2 was conducted where the field was 150 m away from~the
threshing floor; the small axial-flow thresher was operated in
the field. For each ton of threshed rice, 37.7 h of labor were
required to transport sheaves of grain to the threshing floor,
while only 1: .5 h were required for the thresher.”
In the 18th century, George ,Washington used horses
pulling a center-pivoted roller to thresh grain on the second
story of his barn. The threshing floor consisted of wooden
planks set on edge with sufficient space between them to
allow the grain to fall to the floor below.
Threshing rollers, threshing sleds, and disc threshers nre
used for threshing small grains. The Egyptian threshing sled
does the job of 4 or 5 bullocks and cuts the straw into short
pieces I-2 cm long (Fig. 9.15). The straw, called tiben in Ebzypt
and bhzlso in India and Pakistan, is used as bullock feed. A
typical Egyptian threshing sled is 107 cm wide and has 3 axles
on 25-cm centers with four 45-cm-diameter 16-gauge (0.060
in) steel discs on each axle. The crop---usually wheat-is
spread 30-50 cm deep for threshing. In India, a similar type
of disc thresher is called an olpad.
The concept of threshing grain with a threshing roller on
a threshing floor has been modernized, somewhat inefficiently, by some Pakistani farmers who use tractor-drawn disk
such as shown in Figure 4.26 to thresh wheat as their
forefathers used bullock-drawn
threshing rollers or disk
threshers. These means of threshing do not completely
separate the grain from the straw, and further winnowing is
&15. egyptian threshing
Threshing machines are used to thresh small grains,
grasses, sorghums, and legumes. Most are not designed to
thresh maize. Threshers can be classified by power, throughput, cylinder type, number of cylinders, and the direction of
material flow through the machine.
Threshing occurs as the grain passes between the rotating
elements in the cylinder and the stationary elements of the
concave. The primary types of cylinders are the wire loop,
spike tooth, rasp bar, spring tooth, angle bar, and drummy.
The inexpensive wire loop cylinder (Fig. 9.8) is used
almost exclusively for threshing rice.
Spike- (or peg-) tooth cylinders are used to thresh all small
grains. These rugged threshers can be adjusted by removing
or installing spikes on the cylinder, or by bolting stationary
spikes to the concave. Peg-tooth cylinders break dry straw
and make cleaning difficult. Although peg-tooth cylinders are
still used with rice, they have been replaced by rasp bar types
for other small grains and maize.
A rasp bar looks like a large, coarse file. Rasp bars work
very well with most grains and can be adjusted to handie
various moisture contents and grain sizes. However, they are
expensive and difficult to manufacture.
Spring-tooth cylinders are used for easily damaged crops
such as dry bean and peanut.
Inexpensive angle bar cylinders are usually faced with
tough rubber strips and are used for small grains and small
Drummy threshers are used in India and Pakistan, where
the thresher also reduces the straw to lengths of l-2 cm. The
drummy is constructed like a hammermill with a hardened
steel plate on the end of each spoke. The cylinder works
against a concave made of rigid steel bars. Threshing occurs
when the rotating plates force the straw and grain through the
concave grates. An aspirator then separates the kernels from
the short pieces of Straw. The drummy performs best in a very
dry climate, where the straw is easily broken and reduced in
Most threshers have one cylinder. However, by placing
two cylinders in ta,ndem, it is possible to thresh difficult crops
without excessive damage. The first cylinder handles the crop
gently and causes little or no damage. The second cylinder
is more aggressive, since it must thresh the stubborn grain.
Quite often both cylinders are identical, except that the
second cylinder is run at higher speed. Double drum wire
loop threshers use this technique. Two-cylinder threshers
designed for dry bean use a spring-tooth cylinder running at
low speed as the first cylinder to avoid damaging the beans.
A spike-tooth cylinder operated at high speed is used as the
second cylinder to assure that all the beans are threshed.
Most threshers are designed to allow the straw to flow
straight through the machine. The sheaves are fed into the
front of the thresher, and the grain is removed as the crop
passes between the cylinder and the concave. The threshing
occurs in about 120’ of cylinder arc. Reciprocating sawtoothed fins called StI2W walkers toss and fluff the straw mass
to free kernels of grain and move the straw rearward to the
end of the machine, where it is sucked up by a fan and blown
onto a stack.
The axial-flow thresher (Fig. 9.14) was invented at IKRI in
the Philippines as a low-powered thresher for rice. The
sheaves are fed tangentially into the concave opening at one
end of the cylinder. The cylinder is a conventionai spiketooth; however, stationary helical segments fiied above the
cylinder move the straw axially because of the interaction
bemeen the teeth and the helical segments. Thus, instead of
subjecting the crop to only 120” of threshing, it is subjected
to perhaps 300”. Blades welded to the exit end of the cylinder
expel the straw from the machine.
6. North American
tionary thresher.
The stationary thresher (Fig. 9.161 is described by the
diameter and length of the threshing cylinder (measured in
inches); 20 x 28 and 40 x 62 are typical sizes. It performs the
following operations:
feeds sheaves into the machine,
threshes out the grain,
l separates grain from the straw,
cleans the grain,
weighs and records grain weight, and
blows straw and chaff into a stack.
The section of the thresher with the grain-cleaning sieves
had the general outline of a shoe in early machines. Today
the section of a thresher or combine with the sieves continues
to be called the “shoe.”
9.1.4 C’onzbi~~~. The combine is so named because it combines the reaper, the thresher, and the grain cleaner int,o one
mobile machine. The first combines were drawn by tractors,
horses, or mules, but tocfay most combines are self-propelled.
A conventional combine has the same arrangement as a
stationary thresher: a threshing cylinder, straw walkers,
cleaning shoe, and a fan.
A typical self-propelled combine (Fig. 9.17) weighs about
7.5 t. A full grain tank adds another ton. About 85% of tile
weight rests on the front drive wheels. Combines are steered
by the rear wheels, which are often hydraulically powered to
provide additional traction in mud.
The traction components of self-propelled combines are
basically the same as those of tractors or trucks. The main
exception is that most self-propelled combines use an adjust-
1. Cylinder
2. Concave
3. Grain pan
4. Straw walkers
9.17. A conventional selfpropelled combine.
5. Adjustable chaffer
6. Upper sieve
7. Lower sieve
8. Tailings auger
9. Grain auger
10. Windboard
able speed V-belt drive or a -hydrostatic drive. The infinite
speed range allows the speed of the combine to be matched
to its capacity to harvest the grain.
When fields are soft and flotation is a problem, largediameter pneumatic tire+- scmetimes called rice tires--can
be installed. Alternately, @al tires can be installed on the
driving wheels. When a combine is used on soft fields most
of the time, it can be equipped with tracks instead of wheels.
Tracks provide better flotation, but both the purchase price
and the maintenance cost are higher than with pneumatic
tires. Also, tracks do not allow high road speed. If poor
flotation conditions are encountered only occasionally, halftracks can be installed as a compromise.
The reaper function of the combine is performed by the
healer, the design of which depends on the crop. A header
for small grains such as rice or wheat consists of a reciprocating knife to cut the crop, an auger to move the severed
material to the feed opening, and a reel to assure that the
severed stalks fall onto the header. The auger and the sheet
metal supporting the cutter bar and reel are called the
platform. The reel’s height and speed are adjustable. Adjustments can be made from the cab by means of hydraulic
controls in larger combines.
In areas where grain may be damaged by hail or green
weeds, or must be threshed within a very narrow range of
moisture, it is often windrowed and allowed to dry before
combining. Crops such as beans must be combined within a
narrow moisture range and may be too dry to combine
without excessive cracking in late afternoon, so ihe fanner
.allows the windrowed crop to absorb moisture from the night
air, then combines the crop in the morning.
Windrows are gathered and fed onto the combine’s
platform by a windrowpickup, which consists of a wide belt
with spring teeth. The entire unit is attached to the front of
the header. A typical windrow pickup is 3.2 m wide. The
speed of the pickup belt (also known as a draper) can be
adjusted to the travel speed and crop condition.
Row crops such as maize are combi::ed directly by
attaching a snapping head-sometimes called a maize (cord
place of the sickle bar header. Maize heads are
manufactured in twos, fours, and eights for 75 to 1~00-cmrow
A short feeder-conveyormoves the crop from the maize
head or the platform to the threshing cylinder. The feederconveyor is usually a part of the base unit of the combine,
whereas the maize head and the platform are attached to the
feeder-conveyor housing.
Combines uhually have a cab to protect the operator from
dust, noise, rain, and cold. In hot climates, the cab may be
equipped with a fan or air conditioner. Since a large combine
costs about $100,000, it makes sense to place the operator in
a comfortable environment. Besides the controls common to
tractors and trucks, the following controls are located in the
cabs of most self-propelled combines:
pivoting ladder control
unloading auger swing control
l grain tank unloading
threshing cylinder speed control
* cylinder speed tachometer
hydrostatic reel drive control
header drive clutch
separator control lever
concave-cylinder clearance control
header height control
hydraulic lift reel control
straw walker warning horn
Most combines collect the threshed grain in a tank chat
holds at least 1,t of grain. In regions where grain is transported
insbags, a bagging platform and a bag chute to drop the bag
onto the field replace or supplement the grain tank and
unloading auger.
Threshing occurs at the threshing cylinder. The types of
cylinders are the same as those in stationary threshing
machines--rasp bar, spike tooth, and angle bar. Some small
Asian self-propelled combines for rice, such as the one
illustrated in Figure 9.18, use a wire loop threshing cylinder.
Others use a spike-tooth cylinder for harvesting rice.
The rasp bar is the most common type of ,threshing
cylinder in combines. Besides the conventional rasp bar
cylinder (where the material to be threshed ir passed under
and perpendicular to the cylinder and concav<>, the axialflow cylinder is used on many combines because it provides
greater threshing capacity without increasing the overall
dimensions of the combine.
Since the axial-flow design
eliminates the need for a straw walker, the space formerly
occupied by the walker can be used for threshing and
separation. Pzause of the 360” between rotor and concave,
the crop is subjected to a much longer period of threshing than
in the conventional combine.
One self-propelled combine uses an axial-flow threshing
cylinder similar to the IRRI design. Another uses 2 roto,rs, each
one 43 cm (17 in) in diameter. One rotor turns clockwise and
9.18. Japanese selfpropelled combine with two
wire locp cylinders5
the other counterclockwise.
Still another manufacturer uses
1 large rotor, 76 cm (30 in> in diameter. Most axial-flow
combines perform a feeding function in the first 20% of the
rotor length, thresh in the next 40%, and separate grain from
straw in the last 40%.
Reciprocating straw walkers (as shown in Fig. 9.17) are
used on most conventional combines, although a large
European combine with a 1.58-m-wide (5.2-ft) threshing cylinder has 8 pairs of separating cylinders, one behind the other
and in the same plane, to move straw rearward from the
threshing cylinder and to save grain6
Performance of a combine varies with the type of crop,
weather conditions, and skill of the operator. It is impossible
to operate a combine without grain loss. Some grain will not
be picked up by the header, some will not be threshed, and
some will ride out on top of the straw and become lost in the
stubble. A 2-3% grain loss is acceptable; to reduce it further
increases the cost of harvesting, since reducing the rate of
harvesting costs more than the value of the grain saved. In the
US, the top 10% of combine operators experience about 1.5%
loss when combining maize and about 3-4% with soybean.
The average combine is probably operated a ith a grain loss
of 4-8O/ of the crop yiel~d. To reduce grain losses and to
operate at maximum efficiency, electronic grain loss sensors,
straw walker overload warning sensors, and shaft speed
monitors can be installed in the cab.
Hillside combines utilize a pendulum and hydraulic
cylinders to keep the combine body level, even while the
header and the tires remain in contact with the ground as the
combine moves along the side of a steep hill. If the body of
the combine is not level, the grain accumulates on the
downhill side of the cleaning sieves, and the straw tends to
overload the downhill side of the straw walkers. These
conditions cause a loss of grain over the chaffer and out of the
rear of the combine.
Three types of self-propelled combines are illustrated in
Figures 9.19! 9.20, and 9.21.
A combine is similar to a good camera in that the various
adjustments will provide good results if made correctly, but
constant adjustment is necessary to meet changing conditions. When combining, adjustments must be made ciepending on the type of crop, grain moisture, amount of green
110. seFpfopellecl
mblne wlth tangential
yfinderand straw walkers.
A. Rasp bar cylinder
B. Concave
C. Back boater
D. Beater grate
E. Straw walker
F. Shoe
Weight (empty)
11,060 kg (24,460 lb)
4.1 m (13 ft)
9.1 m (30 ft)
4.5 m (14-314ft)
Grain tank
7.6 cu m (221 bu)
Brake horsepower
Travel speed
O-23 km/h (O-14 mph)
1.675 m x 56 cm diameter
(5.5 ft x 22 in diameter)
Combine has a capacity of 15.4 t grain/h when operating at a 3%
total grain loss in windrowed barley yielding 3.3 t/ha (61 bu/acre).
weeds, and crop yield. The major adjustments are made in
cylinder or rotor speed, concave-cylinder clearance, chaffer
opening, sieve opening, fan output, and travel speed.
For wheat, the peripheral velocity of the threshing cylinder should be 22-35 m/set (4300-KIWI ft/min [fpml) and the
concave-cylinder clearance 3-13 mm (P/8-1/2 in>. For rice, the
peripheral velocity should be 20-30 m/set (4000-6000 fpm)
and the clearance 1.5-13 mm (1/16-i/2 in>. Beans require very
low cylinder speed with a peripheral velocity of 7-20 mIsec
(1400-4000 fpm) and a clearance of 13-25 mm (1/2-l in>.
Clover seed requires high cylinder speed with a velocity of 25
41 m/set (5000-8000 fpm) and a clearance of 3-10 mm (l/83/8 in).
During combining, moisture can be transferred from the
straw to the grain, thereby increasing the moisture level in the
grain tank O.l-3% higher than in the kernels in the field.
9.29. Self-propelled
combine with transverse
axial-flow cylinder.’
A. Concave
D. Rotor
G. Grain distributors
B. Cage
E. Discharge paddles H. Accelerator rolls
I. Shoe
C. Helical segments F. Discharge beater
10,960 kg (24,200 lb)
Weight (empty)
Grain tank
8.6 cu m (245 bu)
3.6 m (12 ft)
Brake horsepower
8.5 m (27-3/4 ft)
0 to 38 km/h (O-24 mph)
4.9 m (16 ft)
64 cm diameter x 2.19 m length
(25 in diameter x 7.2 ft length)
Combine has a capacity of 23 t grain/h-when operating at a 3% total
grain loss in windrowed barley yielding 3.3 t/ha (61 bu/acre).
9.2 Rootandtubes
Root and tuber crops such as Irish potato, sweet potato, yam,
cocoyam, cassava, taro, peanut, and sugar beet are hidden
from the farmer at harvest time. Unless the entire mass of earth
about the tubers is lifted as a unit, tuber damage can easily
Cassava is grown throughout the tropics and is usually
harvested by hand. Since cassava tubers can be harvested
over several months and are difficult to store, subsistence
farmers harvest the tubers as required by digging them out of
the soil with a machete and a hoe or a fork. In sandy soil,
tubers can he lifted to the surface by the stem if some of the
topsoil is first removed. The woody stem of a year-old cassava
plant can transmit a maximum lifting force of about 1,500 N
(337 lb) before breaking. To pull a cassava plant from sandy
soil requires approximately 1,000 N (225 lb).
9.21. Self-propelled
combine with longitudinal
axial-flow cy1inder.O
A. Frotor
6. Concave
C. Separating section
D. Back beater
E. Shoe
Weight (empty)
10,240 kg (22,600 lb)
Grain tank
7.3 m3 (206 bu)
4.2 m (13.8 ft)
Brake horsepower
8.7 m (29 ft)
O-26 km/h (O-l 5 mph)
4.6 m (15 ft)
76 cm diameter x 2.73 m long)
(30 in diameter x 8.9 ft long)
Combine has a capacity of 22 t grain/h when operating at a 3% total
grain loss in windrowed barley yielding 3.3 t/ha (61 bu/[email protected]
Experiments in Surinam with a two-person cassava lift,er
demonstrated that a simple cassava lifter was more effective
than a spade in light soil. The lifter is simply a lever with a
3:l mechanical advantage mounted on a stand. A pair of tongs
hangs from the short end of the lever. One person places the
jaws of the tongs around the cassava plant stem while the
other person pushes down on the long end of the lever. Since
a man can exert a downward force of 600 N (135 lb) with his
body weight, the 3:l mechanical advantage of the lever
produces a [email protected] force of 1,800 N (405 lb) at the tongs . Table
9.3 provides a comparison of the two-person lifter and a fork
for harvesting cassava.
ksingle-bottom moldboard plow can be used as a cassava
lifter. If animals are used to pull the plow, they must be well
trained. Studies in Fiji revealed that a single-bottom mold-
board plow mounted on a standard 3-point hitch cf a 40-hp
tractor was satisfactory for lifting cassava roots.‘” Before
plowing the cassava, the stalks were cut IO-15 cm above the
soil surface. The short stem was used to pull the clump of
tubers from the fractured soil after plowing. The aerial parts
of the plant were tossed aside from the patn of the tractor,
which maintained a speed of about 3 km/h while plowing out
the crop. The tubers were handpicked and tossed aside
before being covered by the overturned soil. The Fiji
experiments also tested a tractor-drawn disc plow and a hand
fork. Test results are shown in Table 9.4.
Tractor-drawn cassava harvesters resemble the tractordrawn potato diggers of the temperate regions. The simplest
design is merely a lifting blade. A more mechanized design
uses an inclined blade that passes under the cassava tubers.
The tubers are loosened from the soil and lifted onto a moving
conveyor chain or a reciprocating rack and are separated from
the soil as the machine moves forward. The tubers fall off the
end of the chain or rack onto the ground and are picked up
manually. An even more sophisticated system features a side
loading elevator at the end of the conveyor chain, which loads
the tubers directly into wagons or trucks moving alongside the
Table 9.3. Comparison of fork and 2-person lifter for ralslng cass8va.l’
Cutting off
Tubers left
in soil
Tubers undamaged
on lifted stems
Twc-person lifter
Table 9.4. Comparison of methods of harvesting cassava In Fiji.
Tubers exposed (kg)
Tuber damage (%j
Time required to
harvest (h/ha)a
Persons required (no.)
Tractor and
moldboard DIOW
* Doesnot includetime for removingaerial parts.
Tractor and
disc DIOW
moldboard olow
Man with
In 1978, two cassava hapvesters were evaluated at CIAT in
Cali, Colombia.
The CIAT lifter was a two-row machine adapted to the
three-point hitch of a category II tractor. Two inclined lifting
planes, SOcm wide on l-m centers, corresponded to the row
spacing. The planes elevated the tubers but did not separate
them from the soil. Depth of work was controlled by the
setting of the hydraulic lift.‘2
The second machine was the Australian Richter h,arvester.
It is a category II;one-row, PTB-driven ma,chine with a curved
digger blade. A chain web elevator 1.6 m (5 ft) long directly
behind the blade separated soil from the tubers as they were
elevated about 50 cm above the ground. Depth of work was
controlled by two adjustable land wheels at the rear of the
The harvesters were evaluated in 7-mo-old cassava
planted on ridges, beds, and the flat. Several cassava varieties
wt’re planted. Row spacing of 1 m was maintained in both flat
and ridge plots. Plant densities of 1,000, 5,000, 15,000, and
20,000 plants/ha were obtained by 200~cm, 66-cm, and SO-cm
row spacing as well as by plant spacing within the row. The
beds were 1.3 m (4 ft) wide on the soil surface, with 2 rows
in each bed 90 cm (3 ft) apart. Plant spacings within rows were
adjusted to provide the same densities as the flat and ridged
~p1ot.s.Before harvesting the cassava, the aerial parts of the
plants were cut and removed from the field.
The following observations tiere made regarding the two
Both machines were effective under the test conditions.
The chain web elevator on the Richter harvester laid
the tubers on top of the ground, where the workers
collecting them could easiiy find them.
The small volume of soil displaced in the ridged plots
minimized draft and energy requirements.
Crop density did not appear to affect the quality of
work, except that a higher density appeared to reduce
crop damage by abrasion on the Richter elevator.
Mechanical harvesters left two to three times fewer
difficult-to-harvest tubers (tubers with a spreading type
of root system) than did workers harvesting by hand.
The opposite was trues of the easy-to-harvest varieties,
which produce compact, conical tubers attached directly to the stem.
l Manual harvesting produced the least tuber damage.
Table 9.5 compares the harvesting machines with hand
The mechanization of cassava harvesting requires modification of cultural practices in addition to alterations in
harvesting tools and machines. Uniformity of tuber position
in the row results in lower loss of tubers. Uniformity of
position is enhanced by planting varieties with compact root
systems, growing cassava on beds or ridges, removal of the
aerial portions of the plants before harvest, and care in
planting the stakes.
Potato harvesting can be by hand or by machine. A few
potatoes can be removed from the soil by a person with a
spade. Animals can be used to pull a single-row potato plow
or an elevated potato digger (Fig. 9.22).
In many countries, potatoes are harvested with a farm
tractor equipped with either a spinner, an elevated digger, or
a potato harvester. A spinner is a tractor-*nounted, PTOpowered machine consisting of a share to pass beneath the
potato row and loosen the tubers, and an assembly of
revolving tines that throw the loosened soil and potatoes to
the side. Most of the potatoes land on top of the ground. The
potato spinner is simple and works well in wet conditions.
However, it can bruise the potatoes. Moreover, the potatoes
are not laid in a compact windrow to facilitate manual picking.
Potato spinners are common in Europe but have never been
used commercially in North America.
manual and machine harvesting of cassava.
CMC 94
tubers (%)
9.22. Animal-drawn potato
An elevated digger has a broad share that slides under the
row and loosens the tubers. Since the rear of the share is tilted
upwards, the earth and tubers must be lifted by a steel elevator
chain. The chain is shaken by agitator sprockets so that soil
falls through the elevator as the potatoes are moved rearward.
Chain speed is such that the potatoes and soil are moved
rearward at the same speed that the digger moves forward.
The agitator sprockets are selected according to the specific
soil conditions and potato variety in order to obtain a windrow
of soil-free potatoes with a minimum of bruising.
elevator diggers are two-row machines, because when the
tubers from two potato rows are placed in a single windrow,
less labor is required to pick them.
The potato harvester is really a potato combine, since it
combines the tasks of digging, pickmg, and sorting (Fig. 9.23).
Most potato harvesters are 2-row machines pulled by a farm
tractor of 75 hp or greater. A 2-row harvester traveling at 3.2
km/h (2 mph) with the blade 10 cm deep lifts 8-10 t of soil per
minute. The common means of separating the tubers from the
soil, stones, and clods is the tilted conveyor. This unit is a
variable-tilt picking table manned by two to seven workers.
Some potato harvesters use an air blast to remove light debris
and flat stones. Other machines use rotary brushes to remove
tuber-shaped rocks from tubers. The tubers ride atop the
brush rollers, while the stones fall through the bristles to the
9.23. Potato harvester.
Liquid can also be used to separate tubers from stones.
Although flotation is efficient in stationary installations, it has
not proved successful on field machines. The flotation
solution is heavy and cannot be maintained because of
contamination with soil and debris in the field.
Some potato harvesters are equipped with X-ray sorters.
A thin layer of material passes a bank of X-ray emitters, and
corresponding sensors distinguish tubers from stones and
clods. A commercial harvester uses a bank of 16 pairs of
emitters, sensors, and pneumatically operated support fingers
to distinguish a tuber from debris. When a tuber is identified
by the X-ray sensor, it passes onto the conveyor. If the X-ray
sensor identifies the object as debris, the corresponding
support finger swings away, and the object drops to the
Since it is crucial to use a ground speed that will provide
the proper amount of soil and tubers on the primary apron,
the tractor must have a transmission that will provide a large
selection of gears. Tractors with hydrostatic transmissions are
often preferred for operating potato harvesters.
9.3 Forage harvesting
Forage harvesting refers to the harvesting of grasses and
legumes used in the form of fresh cut: hay, or ensiled fodder
for animals.
9.3.1 Hund tools. Grasses and legumes are reaped with
sickles or scythes similar to those used for harvesting grain,
except that these sickles are not usually serrated, and the
scythes have shorter blades. A machete can also be used for
harvesting forage. When cutting very flexible blades of forage
with a machete, a stick is used to provide resistance to the
impact of the blade.
9.3.2 Mowi-rg
machines.The reciprcs:ating mower (Fig. 9.24)
cuts like scissors by moving a section knife across a mating
surface (ledger plate). It is the oldest and most common type
of mowing machine. It is easily identified by the guards that
separate the crop, lift lodged plants, shield the section knives
at the end of the cutting stroke, and protect the knife from
damage by rocks and rigid obstructions.
The reciprocating mower has low power requirements
and is used for animal-powered machines. Horse-drawn
mowers normally have a 5 ft (1.5 m) cutter bar! while tractor
mowers range from 5 to 9 ft (1.5-3 m). The knife cuts on both
the outward and the return strokes. Throughout the world,
knife sections are manufactured to a width of 3 in (7.6 cm),
and the guards are spaced to the same measurement. Many
mowers made for high-speed mowing have a stroke longer
than the 3-in guard spacing, e.g., 3.75-4.75 in (9.5-12 cm). The
knife moves through the crop at high velocity, with the cutting
side of the knife section within the lip of the guard at the
9.24. Reciprocating mower.
begiting and end of each stroke. Mowers with a long pitman
usually operate at a crank speed of 700-l ,000 rpm, while those
using a rocker mechanism or a 2-throw crank drive the knife
at speeds of l,OOO-2,000 strokes/min.
It is essential that the knife section fit tightly against the
ledger plates for smooth cutting. Otherwise, good cutting
action is rest, and the crop clogs the guards.’ The cutting edges
of the knife sections and the ledger plates must be kept sharp,
and the guards must fit on the bar so that all of the ledger plates
are on the same plane. A pry bar and heavy hammer are often
used to nudge a guard into position. The knife is pressed onto
the ledger plates by hold-down clips, which must be adjusted
The maximum forward spred of a reciprocating mower is
greatly affected by the veloci& of the knife moving across the
ledger plates. The double-kni!c mower has two reciprocating
knives, one above the other. When pressed together and held
in position with a guide about every 15 cm (6 in>, good cutting
action between the upper and lower knife sections is obtained. The doubl&knife rno\t:er does not have guards. In
smooth fields, it is able to mow i;ravy hay crops at high speed.
Thick growth presents no diffi~Gry to this mower. However,
damage from large stones can occur since there are no guards,
A test of a typical double-knife mower with a 1.5-m-wide cut
revealed that the mower operates satisfactorily at speeds as
high as 15 km/h.14 The speed and rate of work are about 50%
higher than those of a conventional reciprocating mower
under the same conditions. The operator’s comfort and safety
are quite often factors limiting travel speed. The double-knife
mower is able to cut closer to the ground than the conventional reciprocating mower, and for this reason it is used
where short stubble is desired.
Most tractor mowers connect the cutter bar behind for
ease of attachment. Other mowers are mounted on the righthand side of the tractor and forward of the driver. ‘Ws
arrangement makes it easy for the operator to watch the action
of the mower and to make sharp turns.
Mowers are
occasionally mounted in front of the tractor for a few specialty
crops. Break-away protection,, which allows the cuttel bar to
swing rearward to prevent a damaging shock load should the
cutter bar Strike an immovable object, is difficult to design on
a front-mounted mower.
Rotary mowers cut by impact rather than scissor action.
Free-swinging knives about 7.5 cm (3 in) long do the cutting.
The knives are mounted on from 2 to 6 high-speed drums or
disks spinning at 1,800~4,000 ‘pm. Typically, three knives are
mounted on the periphery of a disk. While cutting, the knives
travel at about 340 km/h. Rotary mowers are of three main
types: disk, drum, and rear mounted.
The knives in disk mowers (Fig. 9.25) are driven by spur
gears enclosed in a housing that resembles the cutter bar of
a reciprocating mower.
Drum mowers (Fig. 9.26) are supported and driven from
the top. Vertical cylinders (drums) support the driving
mechanism 1.5-2 m above the ground and cut at ground level.
Swinging knives are attached to the bottom of the drums. The
rotors of disk and drum mowers are arranged in counterrotating pairs for ease of manufacturing. The counter-rotating
arrangement is normally satisfactory, although on some grass
crops the pairs of drums tend to deposit the crop in rows
instead of an even swath.
The rear-mounted rotary mower is used for trimming
pastures and lawns. It usually has a vertical drive shaft with
two heavy swinging blades attached to the bottom of the shaft.
Centrifilgal force throws cut herbage from below the sides *{Ed
rear of the mower deck, which is attached to :he tractor’s
three-point hitch.
Flail mowers have free-swinging flails (knives) attached to
a shaft mounted transversely at the rear of the tractor and
powered by the trxtor’s PTO. A sheet metal hood over the
shaft and flails directs the severed crop rearward into a swath
and prevents stones and ot,her objects from being thrown
9.25. Disk mower.
Illustration courtesy of Gehl Company
9.26. Drum mower.
outside of the swath. The flail mower is very similar to a flail
forage h~arvester, except that its rotor operates at a lower
speed. Another difference is that the crop is placed into a
swath instead of being blown through a discharge pipe. By
placing retarding bars between the periphery of the flails and
the hood, stems can be cracked and conditioned to enhance
The power requirement for a rotary or disk mower is
between that needed for a sickle bar reciprocating mower and
that o,f a flail mower. For the same width of cut, a rotary
mower requires five times as much power as a sickle bar
mower, and two-thirds as much as a flail mower. The freeswinging knives that cut by impact give the rotary mower 2
important advantages over the conventional sickie bar: it can
cut ‘70% faster and it cannot be clogged.
A rotary or flail mower is preferred with grass crops, in
orchards where twigs and limbs are difficult for a sickle bar
mower, where there are anthills or woodchuck mounds, or
where the terrain is rough and the hay crop is frequently
lodged. On the other hand, if the field is fairly smooth, the
sickle-bar mower is preferred, since it requires less power,
does not recut the crop, and has a low initial cost. Rotary and
disk mowers have largely replaced double-knife mowers,
since they are capable of mowing at high speed, and the
cutting elements are much easier to replace than are the sickle
knives of the double-knife mowers.
9.3.3 Conditionersand rakes.Grasses and legumes have high
moisture content at mowing time. If the forage is to be stored
as hay, it must be dried to 20% moisture content (MC). If it
is to be stored as haylage (wjlted hay crop silage), it should
be dried to 5565% MC. A tremendous amount of water must
be evaporated from a freshly cut hay crop to convert it to
haylage or hay. Four tons of freshly cut grass or alfalfa at 80%
MC must lose 2 t of water to wilt it to 60% MC before it can
be stored as haylage. If the crop is to be made into hay, 3 t
of water must be evaporated from 4 t of fresh material to
obtain 1 t of hay at 20% MC.
To promote drying of the fcrage where no machines are
available, farmers use hay forks to turn the bottom of the
swath toward the sun and wind. The tedder is a machine that
fluffs up the swath and rearranges the orient:,*ion of the leaves
and stems to the sun and air. Tedders are drawn by both
animals and tractors. The animal-drawn units are reel or kick
type, in which the tines that lit? and rearrange the hay crop are
powered by the ground wheels.
The rotary tedder is tractor powered and available in both
trailing and three-point hitch models (Fig. 9.27). In addition
to tedding, most rotary tedders can form a swath into a
windrow or spread a windrow into a swath. A typical reel
tedder has a swath width of 2 m (6.5 ft), weighs 300 kg, and
is operated at 10 km/h (6.2 mph). Rotary tedders are made
for swaths from 1.5 to 6 m (5-20 ft) wide. A typical rotary
tedder designed to work on a 3.5-m-wide swath weighs
250 kg and is operated at about 10 kin/h (6 mph).
Tedders are more useful with grasses than with alfalfa,
since they tend to knock leaves from the alfalfa stems and thus
reduce its value.
Frequently the top part of a windrow of a drying hay crop
is dry enough to bale, but the bottom is too wet. By inverting
the windrow without tearing it apart as with a tedder, the
wetter underside is exposed to the sun and air to dry, while
the dry top surface is placed underneath. Windrows can be
inverted by flipping them over with the end of aside-delivery
rake. A windrow inverter (Fig. 9.281 is designed specifically
9.27. Rotarytedder.
Illustration courtesy of Ford New Holland, Inc.
to turn windrows without much disturbance to the integrity of
the windrow in a gentle fashion so that dry leaves will not be
stripped away and the wet and dry materials are not mixed.
The windrow inverter shown in Figure 9.28 uses a spring tine
pickup to place the windrow on a transverse rubber belt that
moves the hay to the side where, guided by deflectors, it forms
an inverted windrow as it falls from the belt.
Research conducted in New York State with various types
of tedders arid conditioners to determine their effect in
shortening the drying time for alfalfa revealed that
crops cut with a mower-conditioner dried significantly
faster than crops that had been mowed and tedded with
a rotary or reel type tedder; and
crops cut with a mower-conditioner and tedded dried
significantly faster than crops not tedded.15
The tests revealed that 28 h after cutting, the crop that had
been mowed and left in the Seth
had 27% MC; mowed and
tedded twice, 25%; cut with a mower-conditioner,
22%; and
cut with a mower-conditioner and tedded twice, 20%.
Where alfalfa is the hay crop, leaf loss, cost of tedding, and
the marginal reduction of drying time do not justify the use of
a tedder.
The drying of hay crops with hollow stems such as alfalfa
is enhanced if the stem is crushed or crimped. Unless the
stems are crushed or crimped, the leaves become overdry
before the stems are dry enough to store. Smooth roll crushers
that crush the entire length of stem are not as efficient as
rubber roll crimpers. The crimpers provide more aggressive
crop movement through the condinoning rolls. Also, it is
9.28. Windrowinvertar.
Illustration courtesy of Ford New Holland. Inc.
unnecessary to crush the stem, since crimping it about every
10 cm is satisfactory.
Some hay crop conditioners use swinging tines to abrade
the stems so that moisture can move more easily through the
epidermis. The tines are usually rubber-mounted steel bars
or rigid-mounted plastic fingers.
Mower-conditioners combine mower, reel, conditioning
rolls, and optional windrowing shields into a single tractorpowered or self-propelled machine (Fig. 9.29). The reel
speed is extremely important, because it provides support for
the standing crop while it keeps the cutter bar cleared of cut
material, thus alleviating plugging of the sickle bar. The
peripheral speed of the reel should be 10% greater than
ground speed. Reel tooth action is usually controiled by an
adjustabie cam. Mower-conditioners are available with either
reciprocating or disc mowing elements.
The mower-conditioner is a basic tool in North America
and Europe for conserving the hay crop as hay or haylage.
A comparison of mower-conditioners
harvesting alfalfa in
Wisconsin revealed that the unit with a disc-type cutter bar
had a higher loss of material than the unit with a reciprocating
sickle cutter bar: 5.9% total dry matter loss vs 3.9%. The unit
with swinging rubber-mounted tines to condition the crop
9.29. Mower-conditioner.
Typical [email protected]
Width of cut
Conditioning roll diameter
Average field speed
Average work rate
Peak PTO power
2.7 m
1,450 kg
75 cm diameter
22 cm
5-l 0 km/h
1.3-2 ha/h
7-9 hp
illustration courtesy of Gehl Company
had a higher loss than the one using a pair of rubber flutes for
crop conditioning:
7.2% vs 5.9%.”
In humid areas, grass or legumes grown for haylage are
dried in the swath to about 40% MC, wet basis (wb), and are
raked into a windrow, remaining there until dry enough to
bale. In low-humidity areas, the forage is made into a loose
windrow by the mower-conditioner
and left to dry before
‘baling. The various side-delivery rakes used for this purpose
are cylindrical reei, oblique parallel bar, finger wheel, rotary,
and transverse endless-chain types.
The cylindrical reel rake is usually ground driven, since it
was first designed as a horse-drawn implement. This rake has
spring tines on three or more reel bars, which move in a
cylindrical pattern as they rotate about the center shaft. The
reel bars and the basket in which they operate are towed at
an angle to the swath. Thus, the interaction of the tines and
the forward motion of the rake moves the hay to one end of
the rake and deposits it as a windrow.
Many models of
cylindrical reel rakes can also be shifted into a tedder mode
in which the swath is kicked out to the rear to form a loose
swath. The cylindrical reel type rake is bulky and slow when
compared to other rakes.
The oblique parallel bar rake (Pig. 9.30) is the most
popular rake in North America. The bars are designed so that
the tines remain nearly vertical as they descend into the swath,
move sideward, and lift out. This rake forms a unifori;;
9.30. Oblique parallel bar
Illustration courtesy of Ford New Holland, Inc.
windrow, which is necessary to achieve high performance
from a baler or forage harvester. Adjustments allow the tines
to be tipped forward to make a loose, fluffy windrow, or
tipped backward to make a tightly rolled windrow. Oblique
parallel bar rakes are normally about 3 m wide and are
operated at about 8 km/h (5 mph).
A finger wheel rake (Fig. 9.31) is very simple. It consists
of a frame with a number of independently mounted, largediameter wheels with spring teeth. The wheels are mounted
slightly obliquely to the direction of travel and are rotated by
the tines striking the swath. The wheels are spring-mounted
so they can float and overlap, thus moving the hay sideways
from one wheel to the other. This rake is inexpensive and can
be operated at 8-13 km/h (5-8 mph). A disadvantage of the
finger wheel is that it picks up aftermath from previous crops,
sirice the tines are in contact with the ground. Also, wind has
a negative effect on the rake, since it blows some of the crop
over the top of the finger wheels. Wind guards are sometimes
installed to alleviate this condition.
The rotary rake is the most popular type in western
Europe. This rake has spring tines mounted on stars, which
rotate about vertical axes and are driven by a gearbox from
the tractor’s PTO. The rotary rake resembles a rotary tedder,
and some models can easily be converted into either a tedder
or a swath-turner. A typical rotary rake weighs 300 kg (660
lb) and has 4 rotary stars to provide a working width of 4.8 m
(16 ft).
9.31. Finger wheel rake.
The transverse endless-chain type of side-delivery rake is
a mounted PTO machine with a pair of chains running
perpendicular to the direction of travel. Spring tines attached
to the chains move the hay across the swath to form a
windrow. This rake is not 2s simple or maintenance-free as
the other rakes.
93.4 Forage huruestm. Forage harvesters are used to cut
standing crops or COpick up windrows. Since the machines
chop material into short lengths and then blow it 6-8 m (2026 ft) into a wagon, they are normally powered by tractors of
60 hp or more. Only the multibottomed plow demands as
much power as the forage harvester among ordinary farm
Forage harvesters are available in tractor-mounted, pullbehind, and self-propelled models. They are designed as base
units with various attachments, commonly called heuds in
North America. The head is designed for gathering the crop
and moving it to the cutterhead of the base unit. Common
heads are the row crop, windrow pickup, direct cut, and
snapper. The row crop head’ is for harvesting standing row
crops such as maize, sorghum, and sunflower. The windrow
pickup head is used to pick up forages such as alfalfa or
grasses that have been placed into windrows. The direct cut
head has a wide sickle bar and is used to cut a standing crop
such as alfalfa. Direct cut heads are frequently used when
alfalfa is cut for dehydration, since it is important to shorten
the time between standing crop and dehydration.
A flail forage harvester (Fig. 9.32) is the simplest and least
expensive type of forage harvester. Farmers frequently use
them for the daily chopping of fresh animal forage. The flail
rotor is the heart of the flail harvester. Typically, the rot.or is
equipped with flails (knives) that cut a 2-m swath. The rotor
is driven at about 1,500 rpm; thus, centrifugal force keeps the
flails rigid as they sever the plants just above the soil surface.
The flails are driven so that they move forward into the crop.
Since the forage is usually longer than desired for silage,
retarding bars are often placed on the inner surface of the
rotor hood to reduce the forage length. The lacerated forage
is thrown from the discharge spout by the energy imparted to
it by the flails. The diqtance that the flails can throw the
chopped material is often insufficient.
9.32. Flail forage harvester.
Flail harvesters equipped with blowers can throw the
chopped material into the rear of a trailing wagon, even
against the wind. By placing a transverse auger behind the
flail rotor and a flywheel cutterhead at the exit end of the
auger. a double-cut flail harvester is obtained (Fig. 9.33). It
is possible to cut the long forage into shorter pieces and blow
it with sufficient velocity into a trailing wagon. The cutterhead
knives cut the forage into shorter pieces, but, since the
material cannot be fed into the cutterheacl at a uniform rate,
it is not cut into uniform lengths. In fact, even with six
cutterhead knives instead of three, the actual length of cut is
not half as long as with the three knives.
Precision-cut forage harvesters have feed rolls that control
the speed of forage through the cutterhead to obtain a uniform
length of cut. The combination of cutterhead speed and the
speed of the feed rolls controls the length of cut. Most
precision-cut forage harvesters are set for a length of cut
between 0.5 and 1.5 cm (j/16-5/8 in>.
A cut-and-throw precision-cut forage harvester is designed so that the cutterhead throws the forage through the
discharge spout and into a trailing wagon. When a higher
9.33. Double-cutflail forage
Illustration courtesy of Ford New Holland, ICC.
discharge velocity is desired, a forage harvester with a
separate blower (cut-and-blow) should be used.
Several decades ago, most precision-cut forage harvesters
utilized flywheel-type cutterheads (Fig. 9.341, because the first
forage harvesters were merely ensilage cutters fitted with
wheels and a row crop head. The flywheel-type cutterheads
were satisfactory when the largest farm tractor was about 50
hp. However, as more power became available, and greater
9.34. Precision-cut
harvesterwith row crop
Illustration courtesy of Deere 8 Company
capacity was desired. larger machines bare constructed. For
each unit of increase of throat width, a flywheel cutterhead
required two units of increase in diameter. Flywheel cuUerheads became larger and more expensive. Although it is
possible to make a thicker mat of material go through the
cutterhead, better cutting action is obtained when the mat is
Manufacturers gradually moved from flywheel to
cylindrical cutterheads (Fig. 9.35). A cylindrical cutterhead
can run at higher speed and be made wider than a flywheel
type, thus obtaining a shoq length of cut with a thin mat of
material. Power consumption by a forage harvester according
to function is shown in Figure 9.36. The figure is for a
flywheel-type forage harvester cutting maize at a rate of 16.4
t/h with a 1.25~cm length of cut.‘”
A precision-cut rrltterheac! cuts with a scissors action. To
retain nonragged particles, the knives and the stationary shear
bar must be kept sharp and properly adjusted. About twothirds of the energy consumed by a flywheel type or a cut-andthrow type of precision-cut forage harvester is by the ctltterhead (Fig. 9.36); however, dull knives or a poorly adjusted
shear bar can increase power consumption significantly. It is
necessary to remove the knives from a flywheei cutterhead to
sharpen them-not an easy task. Cylindrical cutterheads are
designed so that the knives can be sharpened in the machine.
The cutterhead is powered at low speed while a sharpening
stone is moved across the cutting edges.
9.35. Precision-cut
cylinder-type forage
harvester and windrow
9.36. Power needs by a
flywheel-type forage
14~14% -
Precision-cut forage harvesters are used primarily to
harvest forage for storage in silos. Since silo unloaders fol
tower silos require a short length of cut to operate sati&ctorily, precision-cut harvesters must be used to harvest forage
to be stored in tower silos.
To produce a finer chopped material than is possible with
knife speed and feed roll speed combinations, a recutting
screen can be installed in a cut-and-blow harvester. Recutting
screens are heavy, curved, perforated steel plates similar to
hammennill screens. They fit closely behind and below the
cylindrical cutterhead and are available with hole sizes
ranging from 1 to ‘IO cm (:$i8-4 in) in diameter. A shorter
length of cut is obtained. but at the expense of more power.
Since forage harvesters are normally operated at full horsepower, the installation of a recutting screen reduces the
harvesting rate.
A forage harvester equipped with snapper-head attachments can be used to snap maize ears and grind them into a
maize and cob mix. The attachments are usually combine
snapper heads adapted for use with forage harvesters. Snapper heads are available only for cut-and-blow machines with
recutter screens.
9.3.,5 Hq IXZ~CXS.
Baling is a method of packaging hay so that
it can be stacked and handled by machinety~ The hlk density
of the bale is important because it affects storage and
transportation costs. If the hayfield is close to the storage
facility, low-density bales of long, loose hay are desirable.
When the bstles must be shipped hundreds or thousands of
kilometers, the hay is formed into cubes or wafers. Bulk
densities of typical hay packages are shown in Table 9.6.
The three major types of pickup ha;r balers are those for
small rectangular bales (Fig. 9.37, large rectangular bales
(Fig. 9.38), and large round bales (Fig. 9.3!4). Rectdngulal
bales have adjustments to vary the length of the bale, but the
Table 9.6. Bulk densities of various forms of packaglng hay.
Bulk density in
Hay package
([email protected])
-Long loose hay
Chopped hay
Baled hay
Grass silage (haylage)
Cubed hav
30 - 60
100 - 200
150 -250
375 - 700
(2 - 4)
(4 - 6)
(6 - 12)
(9 - 16)
(23 - 441
9.37. Pickup baler for
making small rectangular
Bale dimensions
Bale weight (hay)
Bale weight (straw)
Tractor required
PTO power required
Average feed rate
2.9 m (loft)
6.4 m (21 ft)
1.5 m ( 5 ft)
1,750 kg (3850 lb)
36 x 46 x 91 cm (14 x 18 x 36 in)
30 kg (66 lb)
22 kg (50 lb)
60 hp
8 to 35 hp
Illustration courtesy of Ford New Holland. Inc.
9.38. Pickup baler for
making large rectangular
Bale dimensions
Bale weight (hay)
Bale weight (straw)
Tractor required
Average feed rate
2.8 m ( 9 ft)
3.7m (12ft)
3.2 m (10.5 ft)
7,800 kg (17,200 lb)
900 kg (2000 lb)
650 kg (1433)
125 hp
9.39. Variable chamber
baler for making large round
Bale dimensions
Bale weight (hay)
Tractor required
PTO power required
Average feed rate
2.6 m ( 8.5 ft)
4.0 m (13 ft)
2.4 m ( 7.9 ft)
1,750 kg (3850 lb)
170 x 170 cm dia (67 x 67 in dia)
800 kg (1760 lb)
60 hp
8to35 hp
illustration courfesy of Gehl Company
cross-sectional dimensions are determined by the bale chamber and cannot be altered. The standard cross-sectional
[email protected] for balers making small rectangular bales are
1$ x 18 in, 16 x 18 in, and 16 x 23 in (35 x 46, 40 x 46, 40 x
58 cm). The length of small rectangular bales can be adjusted
from about 30 to 125 cm (12-48 in). Two strands of twine or
wire are used to keep the bale compressed and to retain its
shape. The strands are usually against the larger crosssectional dimension of the bale.
Large rectangular bales cannot be handled manually
because of their size and weight . Cross-sectional dimensions
of large rectangular bales range from 80 x 80 cm (32 x 32 in)
to 120 x 125 cm (47 x 49 in>. Five to six strands of twine are
used to hold a bale together.
If a rectangular bale is stored outdoors for several months
in a humid climate, it will mold and rot, since it cannot shed
rain or snow. The round bale was developed for outside
storage of winter feed. In some areas, bales are left where
ejected from the baler, and are used for winter feeding months
later. The hay forming the cylindrical surface ir. round bales
serves as a thatched roof to the rain and snow. There is somr
deterioration of the outside 15 cm C.6in), but the bulk of the
hay remains in good condition. The storage loss of a large
round alfalfa or mixed hay bale stored inside a barn is about
3% of dry bale weight. The same bale stored outside for 6 mo
in humid temperate climate will lose about 15%.Lo
Although balers have been developed for making small
round bales--.35-50 cm in diameter x 90 cm in length (14-20
x 36 in), weighing 20-45 kg (44-100 lb&-they are no longer
commonly used. One type of baler is a very simple machine
that fonns the bale by rolling the windrow between the baler
and the ground. Because the bale is formed on the ground,
the baler cannot carry the bale, but must leave it behind.
These bales are about 2 m in diameter by 2.1 m long, weigh
500 kg, and have a density of about 100 kg/m?.
Another type of round baler picks up the windrow and
feeds it between sets of belts, chains, or powered rollers to
form the bale. The belt- or chain-type bales are usually
variable chamber machines, while the powered roller balers
are usually fixed chamber machines. The variable chamber
machines can make bales of various diameters, while fixed
chamber balers make only one size bale.
The ends of most round bales are not tied with knots. The
twine is merely wrapped on the bale while it is compressed
and rotating in the chamber.
The PTO power requirements for a large round baler are
fairly constant. A typical baler consumes 4 hp at no load. As
hay is fed into the chamber, the PTO power increases to about
15 hp as the bale weight increases to 100 kg (220 lb). The
power requirement remains constant as the bale weight
increases to about 300 kg (660 lb), and then rises to 20 hp as
the bale approaches a weight of 400 kg (880 lb). About 10
dwb hp is required for a large round baler traveling at 10 km/
h (16 mph) on a dry flat field.
9.4 Fiber harvesting
and field processing
9.40. Ripe cotton boll ready
to harvest.
9.4.2 Cotton. Cotton is a perennial crop, but it can be grown
as an annual. The fibers that grow from the seed coat are
called lint. These fibers are the most valuable part of the plant,
although the seeds are also valuable, since they are about 20%
oil by weight. The seed and lint are contained in a seed pod
called a boll (Fig. 9.40). Each boll contains four or five clumps
called lo&s, which contain the seeds and lint. The seeds and
attached lint are called seed cotton.
Cotton can produce up to 3300 kg seed cotton/ha (3000
lb/acre), but the yield is more commonly 1,500 kg/ha (1340
lbiacre), and in primitive conditions it is often as little as 300
kg/ha (268 lb/acre).
Traditionally, cotton is handpicked. A good worker can
pick 45 kg (100 lb) of seed cotton per day in a heavy crop, but
on poorer yields the average is probably 10 kg (22 lb) per
pi~cker per day. Unfortunately, cotton bolls do not open
uniformly, so a field must be picked three or four times
weekly. Cotton should be dry before it is picked. The picker
pulls a sack that can be up to 2 m long. The open end of the
sack is tied to the picker’s waist so that both hands are free to
pick the cotton. Cotton pickers are usually paid by the weight
of seed cotton picked. After weighing, the cotton is put into
30-kg (66-lb) bags and transported to a cotton gin, where the
lint is removed from the seeds. The lint is baled into 227-kg
(SOO-lb) bales.
The disadvantage of harvesting cotton mechanically is
that it usually results in an accumulation of trash-pieces of
leaves, stems, and unopened bolls. The gin must therefore
remove the additional trash. There is no difficulty in giuning
handpicked cotton in a gin designed for mechanically harvested cotton, but cotton from a mechanical harvester can
cause difficulties in a gin designed for handpicked cotton.
An example of a mechanized cotton picker is shown in
Figure 9.41.
Chemical defoliants are necessary in harvesting cotton
mechanically. Defoliation removes leaves, which interfere
with machine harvesting, prevents staining of the lint by green
leaves, and eliminates clry leaf trash, which is difficult to
Mechanical cotton pickers are of two types: stripper
harvesters and spindle pickers. Stripper harvesters operate
best with low-growing, short-limbed plants. At first glance, a
cotton stripper resembles a maize .snapping head for a
combine or maize picker. For each row there is a pair of
stripping rolls about 15 cm in diameter, 1 m long, and set at
about 30” to the horizontal (Fig. 9.42). The rolls consist of
alternate longitudinal rows of brushes and rubber flaps. The
rolls are driven so that they pull up on the plant (opposite to
the direction of rotation of snapping rolls on a maize
harvesting head). The stripper rolls snap off the cotton bolls,
which are discharged into conveying augers and then into an
airstream, which separates the mature bolls from the green,
unopened bolls by blowing them into a storage basket.
Gin turn-out is the weight of recovered lint divided by the
weight of field-run seed cotton and expressed as a percentage. It is sometimes used as an index of the efficiency of the
9.41. Self-piopelied
spindle-type cotton picker.
lllustrafion courtesy of Deere & Company
9.42. Stripping rolls of a
cotton stripper.
harvesting system. In a test of harvesting systems, the gin turnout for hand picking was 37%; spindle picker, 36%; and
stripper harvester, 23%.“*
Instead of pulling the cotton bolls from the plant, the
spindle picker uses revolving spindles to penetrate the plant.
The seed cotton is then wound upon the spindles. In some
machines, the spindles are tapered with three or four longitudinal rows of barbs (Fig. 9.43). The barbs on, the spindles
snag the cotton, which is pulled from the bolls and wound on
the spindles as they rotate at 2,000-4,000 rpm. Other machines
use straight spindles with circular or square cross sections
(Fig. 9.44). Their cross-sectional area is smaller than that of
the tapered spindles, and they rotate at about 1,500 rpm. Both
straight and tapered spindles must be moistened with water,
since a wet steel spindle adheres to cotton better than a dry
spindle, and the water keeps the spindles clean of gum and
Figure 9.43 shows tapered spindles mounted on a drum.
The peripheral speed of the drum is the same as the ground
speed of the machine. There are 2 drums per row, with a total
of 500-600 spindles. Cotton is removed from the tapered
spindles by powered doffer plates.
Some chain-belt types of spindle pickers are designed to
pick from only one side of the rowI while other machines are
designed so that the row passes between a set of belt,s holding
9.43. Top1view of spindle
picker, drum type, with
tapered spindles.
9.44. Top view of spindle
picker, chain type, with
straight spindles.
spindles. A chain type of spindle picker with straight spindles,
as illustrated in Figure 9.44, may have nearly 1,300 spindles.
The spindles rotate only while passing through the cotton
foliage. On the return side, the spindles are not rotated and
the cotton is stripped as the spindles pass between the teeth
of stationary strippers.
94.2 Jute.Jute (Corchorus capsulurisor Corchorus olitorius)
ranks second to cotton in importance as a fiber plant. A jute
stalk at harvest time is 3-4 m high, with a diameter about that
of a man’s small finger. The stalks are harvested between the
time of blooming and the appearance of the seed capsules.
Harvesting is usually accomplished by workers with hand
sickles, who sever the stalks 3-5 cm above the soil surface.
Jute is produced mainly in the river deltas of Bangladesh. It
is often harvested while partially submerged by the annual
monsoon floods. Since the jute plant has a very small root
system, partially submerged plants are harvested roots and all.
The roots are cut off later on dry ground.
Jute yields about 28,000 kg/ha of green crop, although
under excellent conditions, yields of 45,000 kg/ha are possible. Since the extracted dry fiber by weight is about 4-4.5%
of the green crop, a normal crop yields about 1,400 kg dry
Harvesting of jute goes hand in hand with primary
processing. Jute fibers are located in the cylindrical stalks
between the epidermis and a central woody core. The fibers
are detached from each other, the woody core, and the bark
by immersing the stalks in water for a period of days. This
process is called retting. Sometimes jute farmers set up the
stalks in shocks to dry for several days before retting. Other
farmers take their crop directly to the water, where a raft of
IO-15 bundles of stalks with 50-100 stalks/bundle is placed in
the water. Weight is placed on top of the raft to force the stalks
underwater. After 8-10 d, the fermentation progresses to a
stage where the fibers are flexible and can be separated from
the stalk. The stalks are removed from the bundles, and
workers pull the fibers from the stalks with their hands. The
process can be expedited by using a wooden mallet. The
fibers are washed in the water and hung up to dry in the sun.
An experienced person can extract about 3 kg of dry fiber per
Machines have bet::: developed to partially decorticate
jute stalks before retting. By machine extraction, the fiberbearing strips are made uniform, and retting is uniform
throughout the length of the strip, whereas in traditional
retting the thinner tops ret early while the thicker base of the
plant is only partially retted. Machine decortication before
retting reduces retting time to 5-6 d, provides more uniform
fibers, and reduces labor.23
94.3 KenaJ: Kenaf (Hibiscus cannabinwsj is used as a substitute for jute. It has more luster than juke, but is coarser and
less supple. In the 19th century and during World War I, one
variety (Cannabis sativa) was grown in the United States as
a source of cordage. Kenaf is an annual crop with a single
stem about 4 m high. Harvesting and primary processing of
kenaf are identical to that of jute.
9.4.4 Flux. Flax (Linum usitatisimum), a fiber crop of the
temperate zone, is the plant from which linen is made. The
fibers are located in the stem between the epidermis and a
central wooden core. At harvest, the flax plant is 5U-100 cm
Flax harvesting and primary processing consist of six
1. harvesting
4. drying
2. deseeding
5. scutching
3. retting
6. combing
9.45. Ripple.
These operations may consume 1.5-2 yr. Although this length
of time could be greatly shortened by artificial drying, the
weather and the agricultural work load patterns where flax is
grown determine a long time period.
Flax harvest is traditionally accomplished by pulling the
plants out by the roots. Experienced workers require I68 h
to harvest 1 ha of flax manually. Because of high labor cost,
harvesting is usually accomplished by cutting the plants with
animal- or tractor-drawn reapers or mechanical pullers.
However, the reapers waste fiber by cutting too high, and a
pulling machine may scuff or crush the straw where the grip
is applied.
The fibers in the damaged sections may be
weakened during retting. After harvesting, the plants are
placed into shocks and left to dry.
Deseeding removes the seed bolls from the plants. In
primitive systems, the seed bolls are removed by pulling the
plant through an upright steel comb called a rippZe(Fig. 9.45).
A typical ripple consists of a row of iron spikes
in* (3.2 cm?
in cross section and 18 in (45 cm> high with a 3/16-in (5-mm)
clearance at the bottom. The top 3 in (7 cm> of the spike tapers
to a point.*” Ripple deseeding requires about 18-20 Nt of
pulled flax.25 When powered rolls are used for deseeding, the
work is accomplished faster. The flax plants are fed through
spring-loaded metal rolls, which crush the seed bolls. The llax
seed falls onto a screening device, which cleans and collects
it. After deseeding, the flax is rebundled into s&eaves.
Retting is a fermentation process in which microorganisms loosen the bond between the fiber and the rest of the
plant. Repeated exposure of flax to dew by spreading it on
the ground is called dew retting. The immersion of sheaves
of flax in water is called water retthg. In unsophisticated
systems, the flax is placed in ponds or sueams. In systems
with greater control, the flax is placed in large tanks, where
the water temperature is maintained at 30-35 ‘C and retting is
completed in 4-6 d.
After retting, the wet flax straw is spread in a field and
dried in the sun. This is the fourth step in the preparation of
linen cloth.
Scutching, the separation of the fibers from the rest of the
plant, is the fifth step. During this operation, the dry, woody
portion of the stem is crushed and broken by passing it
through a series of fluted rollers. The straw is then held at one
end, and, by beating and scraping, the dry broken pieces of
the stem are removed from the fibers (decorticated).
decorticator is shown in Figure 9.46.
called hackling-is the sixth and final
step. The scutched fiber is drawn manually over a series of
combs. This process removes short, tangled fiber; straightens
the long fibers; and lays them in parallel strands.
mechanized operations, hackling is done during the last stage
of the scutching process.
9.46. Decorticator.
9.4.5 Coir. Coir is the fiber obtained from coconut husks.
“White” coir is produced from green (unripe) coconuts by
manually beating the fibers out from the husk. The fibers are
then spun into yarn and made into mats and other household
products. “Brown” coir is a by-product extracted from the
husks of ripe coconuts harvested for copra, oil, or desiccated
coconut, and is the coir usually referred to in commerce. Forty
coconuts yield about 2.7 kg of The first step in
preparing coir is to husk the coconut by ramming it onto a
stationary spike and ripping the husk from the nut into three
to five pieces. The husks are then retted for 1-6 mo in either
fresh water or seawater to loosen the fibers from the rest of
the husk. Powered steel crushing rolls are often used to crush
the husk before retting to hasten the retting process.
After retting, the fiber is sun-dried and then decorticated.
The dry husks are held with both hands against a powered
roller containing a number of steel spikes called needles,
which strip particles from the fiber. A foot-treadle machine
can handle 3-5 kg of husk (10 pieces) per hour, while a 3-hp
machine tended by three operators has a capacity of 200-250
kg, or 600 pieces per hour. An 8-hp engine-driven decorticator will decor&ate nonretted husks at the rate of 2,000
complete husks in a 10-h day. The fibers from the decortieating machine must then be put through a carding machine
before being made into rope, twine, or mattress stuffing.
9.4.6 Sisal. Sisal @gave sisalana) is used primarily for agricultural baler twine. (Henequen L4gazJejbumvydesl and
maguey L4guue can&z] are also referred to as sisal for
commercial purposes.) Sisal is grown for the fibers contained
in the plant’s fleshy leaves. Sisal leaves are usually about 1.2
m long with a sharp spine at the end of each leaf. Each mature
leaf contains about 1,100 creamy white fibers. A sisal plant
produces 2-3 leaves per month, or 200-250 leaves over its
7- to 12-yr lifespan. .A sisal plant flowers once and then dies.
When the plant is about to flower (pole), a shoot resembling
a giant spear of asparagus arises from the center of the plant
to a height of 5-6 m. A sisal plant from which no leaves are
removed until poling will live about 4 yr? but by regular cutting
of a few leaves from a plant throughout the year, its lifespan
is lengthened and its fiber productivity increased. The’leaves
are cut from the stem with a blade about 18 cm long and 3 cm
wide; 16-18 leaves are left on the plant, except at the last
cutting at poling, when all the leaves are removed.
Under primitive conditions, the fibers are extracted by
beating the leaf to a pulp with a mallet. The fleshy particles
are scraped away by drawing the fibers over the corner of a
block of wood, and then washing them. Sophisticated
decortication is accomplished by engine-powered machines
such as a raspador, or automatic decorticator.
The raspador is a wheel 1 m in diameter and 30 cm wide,
on the rim of which steel bars or.knives are fastened. The
wheel is mounted on a horizontal shaft and driven at a speed
of about 500 rpm. The bottom of the wheel is set about 5-6
mm above a stationary base plate. The operator feeds a leaf
into the space between the wheel and base plate. The
direction of the rotation of the wheel tends to pull the leaf into
the machine, but the operator holds onto the leaf and allows
it to enter the machine at a uniform speed. Fleshy particles
of the leaf fly from the rear of the machine. After the leaf is
halfway into the machine, the operator removes it, grasps the
exposed fibers, and decorticates the other half. One operator
can decorticate 400-500 leaves per hour, although the work
is tiring.
Automatic decorticators consist essentially of a shaft or
drum tu which beater knives are fastened. The leaves enter
the automatic decorticator parallel to the axis of the drum. The
flesh of the leaf is removed as it passes between the drum and
a concave. The leaves are czrried into the throat of the
automatic decorticator by means of a conveyor. An automatic
decorticator can process 25,000 leaves (lo-20 t> per hour.
During and after decortication, the fiber is washed with
fresh water. The fiber is then dried, combed, and baled for
94.7 Abaca. Abaca (Muss text&s1is a member of the banana
family and provides a fiber that is sometimes called Manila
hemp. (The fiber is actually not hemp, but got its name from
the port of Manila from whence it was first exported.) Abaca
is a tropical plant requiring a hot and humid climate, heavy
rainfall throughout the year, and well-drained soil. Abaca
fiber is light buff and lustrous in color and the strongest of all
the natural fibersA In addition to its use in cloth and twine,
it is superb for marine ropes because of its elasticity, strength,
and resistance to salt water.
Abaca stalks can be harvested at about 4 yr of age,
although the plant can live as long as 25 yr. New plantings
are made after 10 yr of harvest, since maximum production
falls off after about 8 yr. Abaca is harvested when blossoms
appear on the flower stalks. Pseudostems at least 2.5 m (8 ft)
long are cut off near the ground, and the leaf sheaths are
stripped off. Each pseudostem has an outside layer that
contains the commercial fiber, a middle layer with a few weak
fibers, and an inner layer of soft tissue with no fibers. By
inserting a machete between the outer and middle layers,
ribbons of the outer layer 6-7 cm wide are stripped off for
processing. The remainder is thrown away.
Manual processing consists of pulling the ribbonscalled tuxks-between.
the knife edge of a machete and a
hard wooden block. A smooth knife edge is used to produce
fine fiber, while serrated blades are used to produce coarse
fiber. A knife with large serrations requires little effort and
wastes little material; a smooth or finely serrated knife leaves
more waste and requires more work. An output of 10 kg of
well-cleaned undried fiber per day by t.his method is considered good. The fiber is hung on lines and sun-dried after
An engine-driven spindle rotating at about 600 rpm can be
used to pull the tuxies between the knife and the wooden
block. The spindle is a cantilevered truncated cone about 15
cm diameter on one end, 10 cm on the other, and about 30
cm long. The conical spindle is whittled out of soft wood,
since hardwood will not provide sufficient friction for the
tuxy. The spindle is located between the operator and the
knife/block assembly. The operator steps on a spring-loaded
lever to open the space between the knife and the bottom
plate, and inserts about half the length of a tuxy under the
knife. Removing his foot and allowing the tuxy to be caught
between the knife and the block, he then wraps his end of the
tuxy around the spindle, as a sailor would wrap a line around
a capstan. The operator then pulls on the tuxy to create
friction on the spindle, which pulls the tuxy between the knife
and block. Since the spindle is conical, the tuxy is easily
released by moving it axially toward the small end. The
operator then flips the tuxy end over end and repeats the
operation until the flesh is removed from the fibers.
Mechanization of abaca fiber production utilizes an engine-driven decorticator similar to the one used for sisal.
When the decorticator is used, the outer sheath is not
separated from the middle and inner sheaths, since the entire
pseudostem is put through the decorticator. First, the stems
are flattened by putting them through a pair of crushing
rollers. Copious amounts of water are used by the decorticator for cleaning the fiber and washing away extraneous
material. A decorticator produces cleaned fiber at the rate of
about 0.5 t/h.
1. Philippine Council for Agriculture, Forestry and Natural Resources
Research and Development (1977) The Philippines recommends for rice.
Los Bafios, Laguna, Philippines.
2. Agricuitumi Engineering Department (1982) Openitor’s manual for
CAAMS-IRRI 1.0 m reaper. International Rice Research Institute, P.O. Box
933, Manila, Philippines.
3. Fernando M D, Palipane K B (1983) A comparative study on buffalo,
tractor, and mechanical threshing in Sri Lanka. RPRDCTecimical Report 141
83. Rice Processing Research and Development Center, Jayanthi Mawatha,
Anuradhapura, Sri Lanka. p. 3-10.
4. Ibid.; p. 8.
5. Shimamoto T, Hiyaniuda S, Fujita S, Nozoe A, Yamaguchi, H, Kabushiki
J (1969) Harvester combine. tJ.S.Patent 3,423,910. Assigned to Kubota,
patented 28 Jan. 1969.
6. Anonymous (1986) Rotary roundup. Power Farming. p. U5. October 1986.
7. Prairie AgricuiturAI Machinery Institute (198181)Report No. E3180D, John
2,-z- ‘820, self-propelled combine. Humboldt, Saskatchewan. Canadd.
8. Prairie Agricuitural Machinery Institute (1981) Report No. E3180B, Allis
Chalmers Gleaner N-6 self-propelled combine. Humboldt, Saskatchewan.
9. Prairie Agricultural Machinery Institute (1981) Report No. E3180A,
International Harvester 1480 self-propelled combine.
Humboldt, Saskatchewan, Canada.
10. Sherma A P (1979) Studies on the mechanized harvesting of cassava in
Fiji. Agric. Mech. Asia 10(2):39-41.
11. van der Sar T (1979) Hand-operated
Asia Io(0:64-68.
cassava harvesters. Agric. Mech,
12. Kemp D C (1978) Harvesting: a field demonstration and evaluation of
two machines. Pages 52-57 inCassava harvesting and processing proceedings, CIAT, Cali, Colombia, 24-28 April, 1978. E.J. Weber, J.H. Cock, and A.
Chouinard, eds. International Development Research Center, Ottawa,
13. Leihner D (1978) Follow up evaluation of two harvesting machines.
Pages 58-59 In Cassava harvesting and processing proceedings, CIAT, Cali,
Colombia, 24-28 April, 1978. Weber, E.J. et al, eds. International Research
Development Research Centre, Ottawa, Canada.
14. Khnner W E, Aspinwell J S (1963) Report on test of Busatis BM 315 KW
National Institute of Agricultural
rear-mounted double-knife mower.
Engineering, Silsoe, England.
15. Campbell J K (1971) An investigation of tedding upon field drying of
alfalfa. Agricultural Engineering Staff Report No. 71-l. Cornell University,
Ithaca, New York.
16. Prairie Agricultural Machinery Institute (1980) PAM1 Evaluation Report
E3179D. International 1190 mower-conditioner.
Humboldt, Saskatchewdn.
17. Koegel R G, Straub R J, Walgenbach R P (1984) Quantification of
mechanical losses in forage harvesting. ASAE Paper 84-1524. American
Society of Agricultural Engineers, St. Joseph, Michigan
18. Blevins F 2, Hansen H J (1956) Analysis of forage harvester dcjign. Agric.
Eng. 37(0:21-29.
19. Prairie Agricultural Machinery Institute (1979) New Holland Model 320
Baler. PAMI Evaluation Report E1978C. Humboldt, Saskatchewan, Canada.
20. Belyea R, Bell S, Mar& F (1984) Large, round bales work well, but ,,..
Hoards Dairyman, August 25, 1984, p. 971,
21. Watson L J (1951)‘Ihe effect of mechanical harvesting on quality. Pages
25-26 in Proceedings of the fifth annual cotton mechanization conference.
National Cotton Council, Memphis, Tennessee.
22. Weindling L (1947) Long vegetable fibers. Columbia University Press,
New York.
23. Mandal T C, Dutta R K, Ojha T P (1987) Principles of mechanical
extraction of base fibre. J. Agric. Eng. 24(2):197-205.
24. Royle J F (1855) The fibrous plants of India. Smith, Elder & Company,
London. p. 216.
25. Hammond J E (1951) Processing of fiber flax in &ego”. Crops In Peace
And War, The Yearbook Of Agriculture 1950-3951; United States Department of Agriculture, U.S. Government Printing Office, Washington, D.C.
26. Royle, op. cit., p. 102-103.
27. Kirby R H (1963) Vegetable fibres. Interscience Publishers, New York.
Avery P J (1963) Hay baling apparatus. U.S. Patent No. 3,110,145; 12 Nov.
Barrington G P, Berge 0 L, Finner M F (1%9) Effect of using a re-cutter in
a cylinder cut forage harvester for chopping low moisture grass silage. ASAE
Paper No. 69-145. American Society of Agricultural Engineers, St. Joseph,
BolIey H I., Marcy W L (1907) Flax culture. Farmers’ Bulletin 274. United
States Department of Agriculture, Washington, DC.
Campbell J K (1986) Reducing potato harvester bruising by adjusting apron
speeds. Agricultural Engineering Idea Sheet 76. N. State College of Agriculture and Life Sciences. Cornell University, Ithaca, New York.
Chuo Boeki Goshi Kaisha (Central Commercial Company) (no date)
CeCoCo guide book for rural cottage and small and medium scale industries.
7th ed. “CeCoCo” Exhibition Demonstration Center, Ibaraki City, Japan.
Dewey L H (1914) Hemp. Pages 283-346 in 1913 yearbook of agriculture.
United States Department of Agriculture, Washington, D.C.
Hennen J J (1971) Power requirements for forage chopping. ASAE Paper
No. 71-145. American Society of Agricultural Engineers, St. Joseph,
Kepner R A, Bainer R, Berger E L (1972) Principles of farm machinery. 26
ed. AVI Publishing Co., Westport, Connecticut.
Quick G, Buchele W (1978) The grain harvesters. American Society of
AgricukuraI Engineers, St. Joseph, Michigan.
Schrock M D, Figutski D L, and McReynolds K L (1975) Hay handling
systems. Report C-537. Kansas State University Extensicn Service, Manhattan, Kansas.
Tracy S M (1903) Cassava. Farmers’ Bulletin 167. United States Department
of Agriculture, Washington, DC.
Grai clrying and storage usually occur at a static location and
are i )I normally included in a book primarily about mobile
tool5 :md field machinery. But the drying and storage of a crop
are affected by its harvesting and transport, and the costs of
growing and harvesting cannot be recovered until the crop is
stored safely. This chapter deals primarily with the basic
principles of drying and. moving air through agricultural
10.1 Basic principles
A grain kernel appears inert. but it is actually a living organism
consuming oxygen and carbohydrates. It produces carbon
dioxide and heat. Fungi are always present, waiting to attack
the grain and cause its deterioration. Between harvest and
safe storage, farmer and fungi are engaged in a race to
determine which will enjoy the grain as food.
Grain can be protected during storage and kept suitable
for human consumption by any or all of these measures:
* drying the grain until fungi are inactive and grain
respiration ceases,
* cooling the grain until fungi are inactive and grain
respiration is nil,
0 placing the grain in an environment with very little
oxygen, and
using a fungicide such as propionic acid to preserve the
In storage, grain must be protected from rodent and insect
infestation, deterioration by extremes of temperature and
moisture, loss through mishandling, mixing with other lots of
grain, and damage by microorganisms.
At harvest, grain and pulses usually contain too much
moisture for safe year-round storage. Grain is often harvested
before it is dry so that it cannot be threshed from the plant by
the wind or eaten by birds and rats while still in the field. Also,
harvest frequently occurs during the rainy season. Better
quality grain can often be obtained if it is harvested before
becoming fully dried on the stalk, and then artificially dried
under controlled conditions.
Moisture content (MC), the most useful and reliable index
of the keeping quality of cereals and pulses, is expressed in
percent and is usually calculated on wet basis (wb):
% MC =
weight of water in grain
weight of water in grain + dry grain matter
x 100
Water molecules in air are in motion and exert a vapor
pressure. The vapor pressure in grain is determined by the
grain’s characteristics, the amount of water in the grain, and
the temperahIre of the grain. If the vapor pressure created by
the water molecules in the grain is greater than the vapor
pressure of water in the surrounding air, the crop loses
moisture to the air until the vapor pressures equalize. When
conditions are reversed, the crop absorbs moisture.
biologicdl material such as grain or forage attains equilibrium
moisture when, at the same temperature as the air, both the
air and the biological material have the same water vapor
pressures. When equilibrium moisture content exists, no
moisture interchange occurs. .4 crop’s equilibrium moisture
content should not be confused with relative humidity (RH).
When is grain dry? In general, grain must be dried to a MC
not greater than its equilibrium :noisture at 70% RI-I and 27 ‘C
(80 “F) for long-term storage. . Table 10.1 lists equilibrium
moisture values at 70% RH and about 25 ‘C (77 OF) for
common grains and other agricultural products. This is the
maximum acceptable level for long-tern] storage.
To dry grain, the vapor pressure of the moisture in the air
surrounding the kernels must be less than the vapor pressure
of the moisture in the grain. The most common means of
lowering the air’s vapor pressure is to heat the air. If the air
temperature is increased while air moisture is constant, the
vapor pressure drops. Decrease in vapor pressure is revealed
by a decrease in RH. For example, if air at 27 “C (80 OF) and
Table 10.1. Equilibrium moisture content at 25 “C (77 OF)and 70%
Equilibrium moisture content
(% wet basis)
Cocoa bean
Dry bean, red Mexican
Dry bean, flat small white
Dry bean, pinto
Peanut, shelled
Maize, yellow dent shelled
Palm kernel
Rice, rough
Rice, polished
Wheat, hard red winter
Wheat, white
Wheat, durum
“At approximately 27 “C (80 OF).
95% RH is heated to 38 ‘C (100 OF), RH drops to 50%; if heated
to 60 “C (140 “F), RH drops to 17%.
When air is cooled and moisture is constant, RH increases
until the dew point is reached, and water comes out of the air
as dew or rain.
The amount of water that must be removed from wet grain
can be calculated by the following equation:
wt of H,O to remove
= wtofwetgrain
per wt of wet grain
where wt =
WG =
DG =
MC =
wet grain,
dry grain,
moisture content wb pa)
100 - MCWG
100 - MCDG-
Example: How many kilograms of water must be removed from 1,000 kg 30% MC grain to dry it to 15% MC?
[1 -
1 -[
85 I
I-~,:, = ~l,OOQx (1 - 0.824)
H,O = 1,000 x 0.176
H,O = 176 kg to be removed
Table 10.2 shows the maximum amount of water that can
be absorbed by air at various temperatures because of
changes in RH when air is heated. The initial condition of the
air is 15.5 “C and 65% RH. (The table assumes 100% efficiency.
In actual practice, only 50~30% of the water will be removed
per hour per 1,000 fP/min 10.47 mj/secl of air.)
The length of time grain may be stored without spoilage
has an inverse relationship to temperature and moisture
content. Although exact data are not available for many
grains. the relationship is well documented for shelled maize.
Shelled maize at 25% MC can be stored at 75 OF(24 “0 for only
4.3 d before deteriorating, but the same maize at 35 “F (2 “C)
can be stored for 42 d before there is significant deterioration
to lower the grade.”
In climates w!lere grain is harvested during the dry season,
harvesting can be delayed while the grain dries to a moislure
suitable for storage. In some areas, farmers break over .i:taize
Table 10.2. Effect of heating upon water-holding caps&y of air.
Water removed/h
Air RH
Per 1000 RVmin Per 106 mVmin
15.6 (unheatedair) 65.0
Air temperature
ears on the stalk so that the ear remains attached, but cannot
receive moisture from the stalk. Many crops .such as rice,
however, shatter badly if dried in the field. Moreover, the
longer a crap is left in the field, the greater the loss due to
wind, insects, and rodents.
Grain density and angle of repose must be considered
during handling, drying, and storage. Wheat weighs nearly
twice as much as oats, and a third more than rough rice. Thus,
the floor of a grain dryer holding wheat must be twice as
strong as a deer holding oats. (In practice, dryers and bins
are usually designed to support the densest grains.)
The angle of repose of filling can be determined by
pouring grain onto a floor to form a conical pile. The angle
between the floor and the tip of the cone is its angle of repose
of filling. The angle of repose of emptying can be determined
by opening one end of a bin of stored grain and allowing the
grain to flow out until the mass of grain stops. The resultant
angle between the surface of the grain and the floor is the
angle of repose of emptying.
The angle of repose of filling is never greater than the
angle of repose of emptying. A grain’s density and angle of
repose interact to exert pressure on the bin walls. The term
equivalentJuid weight takes into account the angle of repose
as well as density, and is used to estimate the force on side
walls of a grain bin. For example, a bin filled with rough rice
to the height of 2 m has a mass of 1158 kg on each square
meter of the fioor (2 m x density of 578.96 kg/m” = 1,158 kg/
ml> and a pressure of 5.56 kPa at the base of the walls (2 m
x 283.5 kg/m” fluid density x 9.80 kgf per newton = 5.56 kPa).
The information given in Table 10.3 is for dry grains used
in commodity trading. Grains with higher moisture usually
have higher angles of repose for both filling and emptying, as
well as higher density
10.2 cribs
A crib is a specialized storage structure designed both to hold
grain and to enhance the drying process. Cribs are used
primarily for drying cob maize <~a; maize). Because of the
spaces between the ears, the interchange-of air and moisture
is facilitated better than if the crib were filled wirh shelled
maize. Cribs perform best in temperate regions, where
storage of undried grain corresponds to the onset of cooler
weather. Figure 10.1 illustrates a typical maize (corn) crib.
Table 10.3. Density and slope characterlstks
Maize, shelled
Rice, rough
Sorghum, grain
Wheat, soft winter
Unit weight
44 1.71
of dry grains.
Angie of repose
n 0
Equivalent fluid weight
- Ib/ft3
a Estimated.
Maize cribs should be constructed and oriented to take
advantage of the prevailing wind. Cribs in humid areas must
be narrow.
In the northeastern USA, unhusked maize can be safely
stored and dried in .1.4-m-wide (4 Z/2-ft) cribs at 40% whole
ear Iv!:;: (35% kernel MCL3 In this region, ear maize is
harvested and stored during October and November. The
dying process is fastest early in the storage period, decreases
trj a minimum during the cold winter months, and accelerates
) completion during the warmer days of March and April.
10.1. Small North
Amarican maize crib that
holds 15 t dry ear maize.
Cob maize shrinks as it dries. Three volumes of wet cob
maize shrink to 2 l/2 volumes of dry cob maize, which in turn
produce 1 l/4 volumes of dry shelled maize.
Husks are usually removed before cribbing to ensure
quicker drying. Where maize with tight-fitting husks is grown
and.pesticides are not used during storage, unhusked maize
should be stored, since the husks provide a mechanical barrier
to moths and insects.
Tobacco barns are essentially large cribs. Their sides are
large doors that can be opened to provide air movement
during good drying weather. During wet weather, the doors
are closed. The tobacco leaves are hung from poles spaced
for adequate air movement.
10.3 Drying with heat
10.2. Shallow layer solar
drying and types of drying in
the Philippines.
Drying with heat does not eliminate the need for air movement. In fact, the heating of moist grain to hasten the drying
process is of no avail unless air moves through the grain and
carries away the water molecules.
Shallow layer solar drying is the most elementary drying
system. The grain is spread to dry in a thin layer on a flat area
exposed to sunlight: packed earth, concrete, matting, or
plastic sheet (Fig. 10.2). The surface of the drying area should
- plastic sheets.
-5a& .
prevent the movement of soil moisture from the drying floor
to the grain. The optimum thickness for sun-drying rough rice
is 2-4 cm.
Grain should be turned during .drying to ensure even
drying and to prevent overdrying of the grain on top. A
wooden rake, scraper, or plow is pushed through the grain to
mix it. Care must be taken to prevent foreign material such
as pebbles and soil from mixing with the grain, as some
kernels m%y he broken. Sun-drying is advantageous in that
it does noi require purchased equipment, except perhaps a
plastic sheet. In many regions in Asia, edges of paved
highways or concrete plazas are utilized to sun-dry rice and
other grains. Since sun-dried grain is exposed, provision must
be made to cover it or to shovel it into conhiners when rain
is imminent.
An investigation of rice production in the Philippines
revealed that conventional solar drying on pavements or hard
earth resulted in significantly lower head rice recovery than
mechanical drying.” Head rice recovev is the percentage by
weight of unbroken kernels of milled rice. Total rice recovery,
which includes both broken and whole grains from the rice
mill, was only marginally lower than that of mechanically
dried rough rice. The recovery rate i,; affected by both the type
of mill in which the rough rice is processed and the drying
Sun-drying research on rough rice revealed that
* if the rice is mixed at half-hour intervals, there is no
significant difference in uniformity of mtiisture distribu\
tion throughout grain depths of 1, 2, 4, a&l 6 cm;
when the rice is mixed at intervals of 2 h or lcnger, or
not mixed at all, grain depth should be 1-2 cm; .>.
total milling recovery is unaffected by l-6 cm rice
thickness if mixing occurs at half-hour imervals;
head rice recovery and the degree of uniformity of rice
MC are directly relateds5
The passive solar dryer (Fig. 10.3) is a glass-covered box
containing a perforated tray that supports the produce. This
type of unit is more often used for drying fruit and vegetable
slices than grain. Its primary advantage is that the glass (or
transparent plastic cover) protects the produce from dust,
insects, and rain. Its secondary advantage is that its design
provides a natural draft that removes saturated air from the
10.3. Passivesolar dryer.
Screen on which
material is laid
10.4. Oil-barreldryer.
dryer. A typical solar dryer has a drying area of about 1.25 mt.
Its framework is made of wood and hardboard sheets; wood
shavings and excelsior are used for insulation. Two sheets of
mylar polyester film 0.13 mm (5 mill thick and spaced 2 cm
apart are used for the transparent cover. The angle of the
transparent cover is determined by the latitude where it is
used. The angle of the absorber to the horizontal should
approximate the degree of latitude. Air flows upward by
natural convection through. holes at the base ,of the cabinet.
It then circulates around the produce, which is placed on a
wire tray positioned several centimeters above the cabinet
floor. The air is then exhausted through holes along the upper
sides and rear of the cabinet.
The oil-barrel dryer (Fig. 10.4) burns fuel to provide heat
without using a mechanically driven fan to force air through
the grain. Its name is derived from an early design that used
oil barrels as a source of construction material.” The grain
must be spread in 1 thin layer, since little airflow through it is
possible. The temperature of the grain should not be greater
than 50-55 ‘C (120-130 OF). Wood, coconut husk, straw, or
other biomass is generally used forfuel. Oil-barrel dryers are
usually wasteful of fuel, and grain temperature is difficult to
The conduction-type continuous-flow drum dryer is an
improvement of the oil-barrel dryer. In some areas where rice
is sun-dried, a serious problem exists during the monsoon,
when it may rain constantly for a week or two.
conduction-type continuous-flow drum dryer is designed to
complement sun-drying. Rough rice harvested at 27% MC
(wb) will heat and spoil in a few days unless it is dried.
Continuous-flow drum dryers such as the IRRI predryer (Fig.
10.5) can dry rough rice to l&20% MC.’ The rice can
subsequently be held for up to 2 wk without deteriorating.
It can then be sun-dried from 18% MC to its storage level of
14% MC.
The conduction-type continuous-flow drum dryer shown
in Figure 10.5 uses biomass such as coconut husk, straw, OK
wood as fuel. Average fuel consumption is about 1 1:g
coconut husk per kg moisture evaporated, or approximately
16.9 MJ gross energy per kg moisture evaporated (7260 BTT.‘/
lb moisture).
The powered conduction-type drum dryer utilizes biomass such as charcoal, ri.ce husk, or coconut husk as the heat
source. The drying cylinder is about 35 cm in diameter and
120 cm long. It is surrounded by an insulating cover mad&
from rice straw and mud piaster. The mud-straw pl;aster
requires replacement after about 4 mo of use.
For drying rice, the drum temperature should not exceed
250 “C (480 OF).for puffing occurs when the rice approaches
10.5. Conduction-type
continuous-flow drum dryer.
Drum temperature
Drum speed
Retention time
Crank power required
Fuel use
loo-150 “C (212-300 “F)
6 rpm
4-6 minlpass
200 kg/h (440 lb/h)
0.03 hp
1 kg coconut husk
per kg water removed
100 ‘C (conduction dryer drum temperature 250 “C). Rice
yellows when subjected to higher temperatures, with a
subsequent ~10s~in commercial value. The dryer can reduce
grain moisture by l-Z% when initial moisture is below 24%,
and by 3-5% when initial moisture is above 24%. Two passes
through the dryer with a cooling interval of one to several
hours reduces moisture content to l&20%. The grain can then
be held until it can be sun-dried to its storage moisture content
of ,14%. Higher head rice recovery is usually obtained with a
conduction-type of drum dryer than with lC3% sun-drying,
but the degree of whiteness of the milled rice may be lower.
The direct burning of biomass is satisfactory for small
conduction dryers, but for larger units it is usually better to
convert the biomass into gas first and then burn the gas in the
dryer. Although the system requires the purchase of a gasifier,
better control of drying temperature is possible, and gas is a
clean-burning fuel.8
In some parts of India, wet grain is dried by mixing it with
hot sand. Heat transfer to the rice is rapid because of the
intimate contact and the great mass of sand. The rice is slightly
parboiled, with gelatinization occurring in the outer layer of
the kernel. A continuous-flow, heated-sand rotary dryer built
at IRRI constantly heated the sand to 150-180 ‘C (300-350 OF);
introduced wet grain into the hot sand at the ratio of about 1
to 20 by weight; screened the dried rice from the sand; and
returned the sand to be reheated. The dryer was able to
reduce moisture by 20% in 15-30 sec. The thermal efficiency
was between 30 and 40%-high
speed demanding more
energy. Tests showed that heated-sand drying of rough rice
above 20% MC (wb) increased head rice yield, but drying of
rough rice below 20% MC at a sand temperature above 1I8 ‘C
(245 OF) decreased head rice yield.”
10.4 Drying with
forced air
Since airflow is useful for absorbing moisture from grain and
transporting it away from the grain, all common drying
systems utilize it. The sun-drying method uses natural airflow
above the grain, while the conduction-type drum dryer uses
air contacting the grain as it cools between passes. It is
possible to hasten drying by constructing a building with a tall
chimney to create an air draft. High-value crops such as hops
are sometimes dried in such buildings.
Airflow is not
controlled by an operator in these drying methods.
Wind is undependable and varies in strength. To obtain
more control over drying, fans driven by electric motors or
internal combustion engines are used for nearly all mechanical drying systems. (The exception is the conduction-type
continuous-flow drum dryer.) The most important part of a
mechanical dryer is a fan to provide airflow through the grain.
To dry grain satisfactorily in a mechanical dryer, minimum
airflow rates must be observed to prevent spoilage. Table 10.4
lists recommendations for drying some common grains.
10.5 Resistanceof
Grains and seeds resist the movement of air. Rough rice offers
twice the resistance of shelled maize. Resistance to ,&flow
depends on the shape and size of the grain, the amount of
trash in the grain, the depth of grain, and the airflow per unit
volume of grain. Airflow resistance is measured as a pressure
drop in inches or centimeters of water.
Pressure drop for specific grains is plotted on Shedd’s
Chart (named for C.K. Shedd, who devised it), shown as
Figure 10.6. The total resistance of grain and ductwork to
airflow is called static pressure (SP). Figure 10.6 refers to clean
Table 10.4. Recommendations for batch-drying of graln.‘O
Ear s~~/~~
Sorghum Soybean
Maximum grain moisture (%)
for drying with
Ambient air
Heated air
Maximum grain moisture
for safe storage (%)
Maximum grain temperature (“C)
when used for
Commercial use
Animal feed
Minimum airflow (air volume
per volume of grain)b of unheated
air for drying grain at a moisture
content of
30 %
25 %
20 %
'40 “C = 104 “F. 83 “C = 180 “F. “Cubicmetersof air per minute/cubicmeterof grain or CFM per cubicfoot of grain.
Pressure drop per meter depth of grain (cm water)
Cob maize as harvested
.03 .04
.06 .06 .l
0.3 0.4
0.6 0.8 1
Pressure dmp per tool depth of grain (inch water)
10.6. Shedd’sChart of
resistanceof grains to
grain. The chart‘s curves of airflow versus pressure drop are
roughly parallel for the various grains and seeds plotted. For
example, barley and rough rice offer more resistance to
airflow than sheiied maize, while soybean offers less. Broken
kernels and fines (small particles of grain) increase resistance.
The ratio of the pressure drop for grain with fines to that
of clean grain at the same airflow rate is called the pack factor.
US Grade No. 2 shelled corn (maize) with maximum broken
kernels and foreign material (3% by weight) has a pack factor
of 1.2.” A poor grade of maize such as No. 7, with about 10%
fines, can have a pack fal:tor of 2.3, which means that the
resistance to airflow is the same as that of clean rough rice.
The concept of pack factor and the fact that the airflow versus
pressure drop curves are roughly parallel can be combined so
that all agricultural seeds can be compared with clean shelled
maize. Wheat, has a factor of 3.48, while ear maize and baled
hay have factors of 0.22.
The effect of resistance to airflow is illustrated in Table
10.5. It is assumed that a 7 I/Zhp fan is used to move air
through the perforated floor of a 7-m diameter bin dryer
containing shelled maize.
Table 10.5. Effect of fines on airflow through qhelled maize.
Pack factor
shelled maize
.of 1.2
Height of grain (ft)
Fdn ,airflow (cfm)
Airflow (cfm/W grain)
Air velscity. (Wmin)
Static pressure (in of water)
Press drop/ft depth.(in of water)
Pack factor
of 2.3
In each case, the fan is a rate demanding 7 I/2
hp and is delivering 10 volumes of air per minute per volume
of grain. In the case of maize, however, with 3% fines (pack
factor 1.2i, the height of grain must be reduced byO.1 ft (3 cm)
to keep the airflow per unit volume of grain constant, The
grain with the pack factor of 2.3 had to be reduced by 14% in
height to keep the airflow per unit volume of grain constant.
10.6 Fan
Various types of fans are used for drying crops. A fan
delivering sufficient airflow against a l-in SP may be unable
to move any air against a 4-in SP. Pans are classed by airflow
(in cfm) at the SP (inches of water column [IWCI) create’d by
the resistance of the air duct and the grain. To design a djring
system, it is insufficient to cite only the fan’s diameter and hp.
A fan curve that plots airflow vs SP is also required.
Table 10.6 lists the performance data of two 7 l/2-hp fans
used for crop drying. If a fan is needed to dry a crop such as
cob maize with little resistance to aifflow, fan A should be
used, because it produces greater air volume at low SP. To
dry a crop with higher resistance to airflow such as rough rice,
fan C should be selected. Note that fan C moves over 10 times
as much air against a SP of 6 IWC’as does fan A.
The two major fan types for drying agricultural products
are the propeller fan and the centritigal fan. The propeller
fan is usually less expensive and provides a large volume of
air against low SP. The centrifugal fan, on the other hand,
provides a large volume of air against high SP. The propeller
fan is noisier than a centrifugal fan of the same horsepower.
The propeller fan is generally used when the SP is below 3
IWC. The centrifugal fan is designed to operate above 3 IWC.
Fan A (Table 10.6) is a propeller fan, while fan C is centrifugal.
Table 10.6. Typical fan performance data for two 7 l/2-hp fans.
Static pressure
(in of water)
1 .o
Airflow (cfm)
Fan .A.
Fan C
Occasionally, more than one fan blows air into a common
plenum chamber. A fan performance chart can determine the
total airflow by summarizing the flow of each fan at a common
SP value. For example, if fans A and C in Table 10.6 blow air
into a common plenum, the resultant airflow at 0.5 IWC SP is
14,250 + 10,350 cfm, or 24,600 cfm. At 3.0 IWC SP, the airflow
is 9,000 + 8,980 cfm, or 17,980 cfm. At 6.5 IWC SP, it is 0 +
6,250 cfm, or 6,250 cfm. In the last case, although both motors
are running, no more air is delivered than by fan C alone, since
fan A cannot move air against a SP of 6.5 IWC.
A grain dryer can use ambient air as the drying medium;
but for faster drying, heat is frequently used (refer to Table
10.2). Moisture content differences in grain between nondry
and dry states are called points of moisture in the USA. If grain
is dried from 19 to 14% MC, 5 points of moisture are removed.
10.7 Combined
forced-air and heat
Most grain dryers using solar heat or clean fuels such as
electricity, natural gas, or propane to heat the air are directfired. All products of combustion pass through the grain being
dried. Burners using wood, biomass, coal, or oils are indirectfired, because the products of combustion do not pass
through the grain. Indirect-fired units do not contaminate the,
grain but are more expensive than direct-fired units. There are
four basic forced-air drying methods, any one of which can
be the best choice depending on the specific conditions.
Drying in storage
- Sack
- Low temperature
- Layer
Batch dryers
- Batch-in-bin
-- Small flatbed
-- Recirculating batch
0 Continuous-flow dryers
- Nonmixing
- Mixing
- Continuous flow in bin
Combination dryers
- Dryeration
- Combination
Drying in storage is a method in which the grain is placed
in the storage container (a crib, for example) before being
dried. Fans are utilized to move the air, and heaters to
warm it.
A sack dryer is a system in which porous sacks such as
burlap containing grain are piled to form a tunnel. Air
(ambient temperature or heated) is blown through the tunnel,
thereby drying the grain. Another sack dryer method makes
use of a perforated floor, with each sack placed over an air
duct. Sack dryers are more labor intensive than most forced
air systems. However, the method is suitable if grain is stored
in sacks and the amount is not large. Research stations often
use this method for drying small quantities of grain.
The element common to low temperature, layer, and
batch-in-bin drying systems is the circular steel grain bin with
a perforated floor. Air is blown up through the grain by a fan
and exhausted at the top of the bin. A heater placed in line
with the fan can heat the air before it goes through the grain.
The grain is not moved or circulated during the drying
process. Air outlets must be open when drying grain in a
storage bin. If the outlets are closed, the inadequate airflow
increases SP, and the moistened air is not exhausted as rapidly
as desired. Figure 10.7 shows a typical grain bin.
Drying with unheated air is much slower than drying with
heated air. For example, air heated to 60 “C will absorb 8 times
the amount of moisture as air at 15 ‘C. IJnheated air drying
is satisfactory for small quantities of grain under 25% MC,
10.7. Grain bin used for
Drying with unheated air
Minimum air flows
Maximum grain moisture
Maximum depth of wet grain
Low temperature drying
Minimum airflovP
Maximum depth
Layer drying
Minimum airfloti
Maximum depth
= 25%
= 1.5 m (5 ft)
= 2.5 for 26% MC
= 1.5 for 24% MC grain
= 0.8 for 22% MC grain
= 5 for 30% MC
= 4 for 25% MC grain
= 5 m (16 A)
BAirflow in m3of air per min/m3 of grain or W of air per min/fP
of grain.
although continuous fan operation for up to 1 mo may be
required to dry the grain to a safe storage level.
Dryers should be operated continuously until the grain is
d,ried. During damp weather, some farmers turn the fan off
to avoid rewetting the grain. This is a mistake. While it is txue
that some of the grain at the bottom of the bin may absorb a
little moisture, grain continues to dry, and the moving air
keeps it cool. Shutting off a fan during drying invites mold and
Low temperature drying is sometimes practiced in the
temperate zone when the temperature is between 0 and 10 ‘C.
The air is heated to increase air temperature about 5 OC, the
burner is controlled by a humidistat, and the fan operates
This drying method is used to keep fuel
consumption down.
In the layer drying method, the bin is lined with successive
layers of wet grain as each preceding layer dries. For example,
when drying rough rice in a 5.5-m-diameter bin, 5 m deep,
using a 7 1,/2-hp fan, and when drying air temperature is
35 ‘C and MC is 28%, the following procedure could be used:
First fill
2.1 m (7 ft)
Second fill
Third fill
When the top of the first layer has dried to 17% MC, the
next layer is added. Approximately 3 l/2 d are required for a
layer to dry to 17% MC. Note that each successive layer is less
deep, since the increasing depth of grain means that less air
is available. Drying speed depends on airflow per unit
volume of grain when the drying air temperature and grain
moisture remain unchanged. The drying air temperature in
layer drying systems is frequently limited to a 10 ‘C (18 “F)
increase over ambient temperature.
The dryer is only one element of a drying system. Many
farmers experience difficulty not with their dryers, but with
obtaining smooth movernent of wet grain from field to dryer
to storage.
The bin dryer used in the batch-in-bin system is usually
constructed so that one day’s harvest can be placed in a layer
about 0.6-1.2 m deep; and then be dried, cooled, and
transferred to storage within 24 h. Drying temperature is 5075 ‘C (120-170 OF) while airflow is 12-50 volumes of air per
minute per volume of grain. One batch takes up to 20 h to
dry. A stirring device should be used for air temperatures
greater than 60 “C (140 OF). At the end of the harvest season,
the dryer is usually operated as a layer-dryer system or a lowtemperature dryer system to fill the bin for grain storage.
The small flatbed dryer consists of fan, heat source,
controls, and bin. The bin has a perforated bed, which is flat
or inclined to facilitate unloading. It holds 1-2 t of grain up
to 0.5 m deep, depending on the crop being dried. The space
between the perforated bed, the walls, and the floor serves as
a plenum to diffuse the air uniformly throughout the grain. An
essential control is a fan switch to cut off fuel to the burner
10.8. Flatbed dryer showing
fan, burner, and bin.
Grain depth
Drying rate
Fuel consumption
should the fan stop. Some dryers are also equipped with a
thermostatic control to automatically control temperature,
and a humidistat to adjust air temperature to grain moisture.
The small flatbed dryer (Fig. 10.8) can be constructed with
simple tools. The fan, however, must be designed and
constructed with care to obtain the desired airflow/SP characteristics. Using a truck fan or a fan from a junkyard will not
do a satisfactory job and will be wasteful of energy.
In a batch dryer, if the air temperature is high and the layer
is thick, the grain at the bottom may be seriously overdried by
the time the grain at the top is dried to the moisture content
required for storage. Table 10.7 cites the results of drying
rough rice 43 cm deep in a flatbed dryer using various air
The rough rice dried at the higher temperature exhibited
greater breakage during hulling than did t,hat dried at the
lower temperature.
The drying procedure is the same for flatbed dryers and
batch-in-bin dryers. The bin used for a batch-in-bin opera-
3-hp gasoline engine or 2-hp electric motor
47-cm-diameter vane-axial
kerosene burner or rice hull furnace
30-50 cm
For 30 cm depth of grain, 43 “C air temperature, and airflow of approximately
1800 cfm at 0.8 in of water, rough rice dries from 22 to ‘14% MC in 4 h.
0.75 liter gasoline/h,
2.0 liter kerosene/h, or
3-4 kg rice hull/h (1 t rough rice contains approximately 200 kg of hulls,
sufficient to dry 1 t rough rice)
Table 10.7. Effect ef alr temperature on drying rough rice in a flatbed
in&l moisture content (% wb)
Drying time (h)
Rough rice moisture at top (% wb)
ftough rice moist&e at center (% wb)
Rough rice moisture at bottom (% wb)
Average rough rice moisture of bin (% wb)
49 “C 60 “‘2
71 “C
(120 “F) (140 OF) (160 “F)
tion, however, is circular, with a roof that can be used for grain
storage. Fiatbed dryers cannot be closed and used for grain
storage, since they have no roofs.
Recirculating batch dryers are cylindrical or cubical in
shape, as shown in Figure 10.9. They hold 12-20 t of grain per
batch. When the dryer is loaded with a batch of wet grain, it
automatically circulates the grain through the drying zone.
The dryer moves the grain so that grain temperature does not
exceed about 60 ‘C, although air temperature may be 65120 ‘C (150-250 OF). The airflow is 30-85 volumes of air per
minute per unit volume of grain.
10.9. Racirculating batch
grain movement
, Direction of
air movement
Removing 10 points of moisture requires 2 h of drying
plus another 30-45 min to cool the grain before removing it
from the dryer for storage.
Contmuous-flow dryers are forced-air dryers designed to
continuously receive wet grain and discharge dry grain. In
nonmixing continuous-flow dryers (Fig. lO.lO>, wet and dry
gram do not mix, while in mixing-type continuous-flow
dryers, they are mixed during the drying process. The
integration of wet and dry grain handling equipment associated with different dryers is important, but in the case of
continuous-flow dryers it is essential. Storage bins for arriving
wet grain must be available, and the dry grain must be moved
into storage as soon as it flows from the dryer. Continuousflow dryers use air temperatures up to 120 OCand airflows of
40 to more than 80 volumes of air per minute per volume of
Nonmixing continuous-flow dryers that dry grain in thin
vertical columns in one pass are quite common (Fig. 10.10).
Wet grain enters at the top of the dryer and is cooled toward
the bottom. Adjustable speed discharge rolls control the
length of time the grain is Exposed to the drying air.
A typical North American unit 2.5 m (8 ft) wide x 8.5 m (28
ft) long x 4.5 m (15 ft) high weighs 5 t. The grain layer
thickness is 30 cm (12 in>, and the burner can consume 120
. Nonmixing
uous-flow dryer.
Screw conveyor
10.11. Mixing continuousflow dryer.
liters (32 gal), of liquefied petroleum gas (LPG) per hour. Fifty
horsepower is required to drive the two 91-cm-diameter
(36-h> axial fans. Airflow through the grain is normally g0 or
more volumes of air per minute per volume of grain. Drying
air temperature is between 60” and 120 ‘C (140-250 OF).
Using 80 ‘C (175 OF) airflow, the dryer will remove 5
points of moisture per hour from shelled maize. Continuousflow dryers are designed to remove grain moisture rapidly.
They therefore require higher engine power to drive the fans
and more fuel to heat the air.
Mixing continuous-flow dryers (Fig. 10.1 Ii are similar to
the vertical nonmixing dryers in that the wet grain enters on
top and the dry grain exits at the bottom. Some dryers feature
stationary baffles that tumble the grain as it flows down the
vertical columns.
The Louisiana State University (LSU) dryer is a mixing
dryer that mixes the grain as it moves
downward past alternately spaced hot air inlets and moistureladen outlets. The inlets and outlets are shaped like inverted
Vs, and the rows are staggered so that the grain mixes as it
tumbles downward (Fig. 10.12). Chaff and fines are blown out
the outlets. Grain flow and moisture removal are controlled
by the speed of grain removal from the bottom of the dryer.
Some grains can be dried in a single pass through the LSU
dryer. Grains such as rough rice, however, are passed once
10.12. Flow pattern in the
LSU mixing-typedryer.
Grain flows
through the dryer to remove about five points of, moisture.
The grain is then tempered (steeped) in a bin, which causes
the moisture in the kernel to flow from the center toward the
exterior layer of the kernel. The grain is then passed through
the dryer again, and the cycle is repeated until the grain is
High-speed dryers often utilize a drying cycle that tempers
the grain to obtain greater energy efficiency and to reduce
stress cracking of grain due to high rates of moisture removal.
is also :ICW! +Y:::::T L,
: ~‘- a& ~~Jiiillii.iOw+
flow dryers, Although these dryers remove the surface moisture on grain kernels easily, time is required for internal kernel
moisture to flow to the kernel’s exterior. Tempering the grain
provides that time.
Continuous flow in a circular bin dryer can be obtained by
using a sweep auger to remove the thin dry layer of grain
adjacent to the perforated floor. The dry grain is then elevated
to the top of tne bin, thus slowly circulating the entire grain
mass over the intensive drying area adjacent to the perforated
Dryeration and combination drying facilitate inpreasing
the throughput of a high-temperature dryer, since the grain is
cooled not in the dryer, but in a tempering or storage bin.
The dryeration system was developed to prevent stress
cracking during high-speed (high temperature and rapid
cooling) drying of grain such as shelled maize. An additional
benefit of the system is the reduction of heat loss in the cooling
phase. In a dryeration system the grain is dried to about two
points above its desired storage moisture level, but it is not
cooled before it leaves the dryer. The hot grain is transferred
into a circular grain bin with a perforated floor and a fan. After
4-6 h of tempering, the fan is turned on and the grain is dried
a final two points of moisture as it cools. The dry grain is then
transferred to a storage bin. The dryeration bin requires an
airflow of 0.5 volume of air per minute per volume of grain
based on full bin capacity.
The combination drying system was developed to reduce
the cost of fuel for heating the drying air. Grain such as shelled
maize is dried to about 19% MC in a high-speed hot air dryer.
It is then transferred to a bin-type dryer used as an unheated
air or low-temperature dryer, and dried for about a month
until it reaches a storage moisture content of 14%. Another
advantage of the combination sys*:emis the reduction? of stress
cracking. The grain is often stored in the final drying bin.
1. Hall D W (1970) Handling and storage of food grains in tropical and
subtropical areas. FAO Agric. Dev. Pap. 90. Food and Agriculture Organization of the United Nations, Rome.
2. United States Department of Agriculture (1969) Guidelines for mold
control in high moisture corn. Farmers’ Bull. 2238. Washington, DC.
3. Wiggans RG, French 0 C (1958) Farm storage of ear corn in the northeast.
Agric. Exp. Sm. Bull. 926. Cornell University, Ithaca, riew York.
4. Duff J B, Toquero T (1975) Factors affecting the efficiency of mechanization in farm level rice poshproduction systems. Ag. Econ. Pap. 75-04.
International Rice Research Institute, P.O. Box 933, Manila, Philippines.
5. Gayanilo V G, Jeon Y W (1987) Sundrying of paddy: effects of mixing
frequency and paddy layer thickness on milling quality, moisture content
distribution, and drying time. Paper presented at the 10th ASEAN Technical
Seminar on Grains Post-Harvest Technology, Aug 1987, Bangkok, Thailand.
6. Lindblad C, Druben L (1976) Small farm grain storage. VITA Manual Ser.
35E. Volunteers In Technical Assistance, Mt. Rainier, Maryland.
7. Jeon Y W, Halos L S, Elepaiio A R (1987) Design and performance
evaluation of an IRRI pre-dryer. Paper presented at the 10th ASEZAN
Technical Seminar on Grains Post-Harvest Technology, Aug 1987, Bangkok,
8. Stickney R E, Piamonte V N, Belonio A T (1987) DA-IRRI rotary paddy
dryer with rice hull gasifier. International Rice Research Institute, P.O. Box
933, Manila, Philippines. p. 4-7.
9. Arboleda J R (1973) Accelerated conduction drying of paddy. P&per
presented at the Annual Convention of the Philippine Society of Agricultural
Engineers, 25-26 Jan 1973, Manila, Philippines.
10. Canadian Department of Agriculture (l%l)
Section 3.1. Ottawa, Canada.
Drying and conditioning.
11. Grama S, Bern C J, Hurburgh C R (1981) Airflow resistance of mixtures
of shelled corn and fines, American Society of Agricultural Engineers Pap.
81-3526. American Society of Agricukural Engineers, St. Joseph, Michigan.
12. Catambay A B, de Padua D B, Arboleda J R (l%O) Drying of rough rice
with heated air in flat bed dryers. Philipp. Agric. 44(2,3):75.
Bockhop C W, Jeon Y W, Halos L S (1983) Design and development of a
furnace for efficient burning of agricultural wastes. Paper presented at the
1983 Grains Post-harvest Workshop, May 1983, Sindanglaya, Indonesia.
Bockhop C W, Jeon Y W, Halos L S (1984) A warehouse-type dryer for drying
and storing agricultural commodities. Paper presented at the 10th Intemational Congress of Agricultural Engineering, International Commission of
Agricultural Engineering, Sep 1984, Budapest, Hungary.
Boumans G (1985) Grain handling and storage. Developments in Agricultural Engineering 4. Elsevier, Amsterdam.
Demegillo J A, Maranan C L,.Jeon Y W (1985) Technical and economic
evaluation of selected types of mechanical dryers. Paper presented at the
ASEANTechnologySeminar on Post-harvest Technology, Aug 1985, Manila.
Elepailo A R, Halos L S, Jeon Y W (1982) Rice hull carbonizing and char
Paper presented at the 37th Annual Convention of the
Philippine Society of Agricuhural Engineers, Apr 1982, Manila.
Bspanto I H, Andales S C, Belonio A T, Jeon Y W (1985) Performance
evaluation of the IRRI batch-type and rotary drum dryers. Paper presented
at the ASRAN Technology Seminar on Post-harvest Technology, Aug 1985,
Halos I. S, Jeon Y W, Bockhop C W (1983) Design and performance of a
multi-purpose dryer using non-conventional energy sources. Paper presented at the 33rd Annual Convention of the Philippine Society of
Agricultural Engineers, Apr 1983, Baybay, Lejrfe, Philippines.
Jeon Y W, Halos L S, Bockhop C W (1982) Design of a center-tube type
furnace for efficient rice hull burning. Paper presented at the National
Workshop on Rice Husk for Energy, Aug 1982, New Delhi, India.
Lawand, T A (1966) A solar-cabinet dryer. Solar Energy 10:4
Ripp B E, Banks HJ, Bond EJ, Calverley D J. Jay 8 G, Navarro S, eds. (1984)
Controlled atmosphere and fumigation in grain storages. Elsevier, New
Vo-Ngoc D, Longval J R, Srivastava N K, Jeon Y W, Halos L S (1987) Wind
tunnel testing of IRRI vortex wind machine. Paper presented at the 10th
ASRAN Technology Seminar on Grain Post-harvest Technology, Aug 1987,
Bangkok, Thailand.
Wimberiy J E (1983) Technical handbook for the paddy rice postharvest
industry in developing countries. International Rice Research Institute, P.O.
Box 933, Manila, Philippines.
Good transport is essential both for getting produce to market
and for getting urban goods to rural areas. It is important that
transport be both efficient and cost effective. In the late 1970s
a large foreign aid project in North Shaba Province of Zaire
attempted to increase the production of maize for the workers
in the mines and factories of South Shaba. Much money was
spent in the local manufacture of hand tools, training centers
for agricultural cooperatives, special programs for women, an
extensive maize breeding program, and road-building.
Analysis surprisingly revealed that the most important factor
in increasing maize production in the project area was road
construction. The roads allowed the grain traders to drive
their trucks to the farm villages to purchase the maize.
Good roads encourage transport for both goods and
people. This chapter is about the various means of transport
used to move prodiace from the farm to the main highways,
railway depots, or market towns.
Transportation by boat is admittedly important. In some
countries such as Bangladesh, much produce is transported
by waterways. Only land transport, however, will be discussed in this chapter.
11.1 Manualtranspc~
Transporting cargo by humans was discussed briefly in
Chapter 1. Carrying poles, handcarts, and bicycles are
improvements on carrying headloads long j&stances, but a
bicycle requires at least a smooth trail, and handcarts require
The energy required to propel a wheeled vehicle such as
a bicycle, wheelbarrow, or handcart depends on the road
surface, the wheel size and construction, the type of wheel
bearing, and the weight of the load. In general, the larger the
wheel diameter, the better, for a large-diameter wheel is less
affected by pebbles and surface unevenness than A small one.
The width of the wheel is not very important on a smooth,
hard surface; but on soft soils a wide wheel will offer lower
resistance to rolling than a narrow wheel. The importance of
this phenomenon is illustrated by the fact that indigenous
vehicles for rural use, ‘from the wheelbarrow in China to
oxcarts in India and Paraguay, have large wheels with wide
rims. The pneumatic tire, with its ability to absorb the pebbles
or road irregularities that cause sudden resistance to the
forward motion of a steel-rimmed wheel, is preferable to a
steel wheel for a human-powered. vehicle.
Although wood bearing and steel axle or babbitt bearing
and steel axle combinations are quite satisfactory for wheeled
vehicles, these types of bearings are frequently of poor quality
in developing countries. Thus, for manually powered vehicles, sealed precision ball, tapered roller, or needle bearings
are preferred.
11.1. Bamboocarrying pole.
11. I. 3 Carryingpole. Bamboo carrying poles such as the one
illustrated in Figure 11.1 are an important means of transporting goods in Asia. Carrying poles provide the bearer a high
degree of mob&y, yet allow transportation of heavy loads-
up to 100 kg. Carrying poles are semicircular in cross-section
aird usually about 2 m long, with tapered ends, The load is
suspended from the ends, and the weight is positioned over
the~bearer’s center of gravity. By contrast? a load carried in the
arms must be supported in an awkward, off-center, fatiguing
posture that can strain the lower back muscles.
A properly designed carrying pole acts as a leaf spring and
reduces the magnitude of the shock load when the bearer lifts
the burden with a vertical movement, Although the load
carried by~the bearer remains constant regardless of how the
burden is carried, the less shock load transmitted to the
bearer, the less tiring is the carrying of the load.
One analysis of the bamboo carrying pole describes it as
a single degreeof-freedomspring-masssystem.’ The analysis
assumes that the mass of the spring is negligible in comparison with the load, and any damping is small. The natural
frequency of the carrying pole and the load depends on the
weight of the !oad and the spring rate of the pole. The bearer’s
stride in steps per second is called the driving frequency. If
the pole were rigid, the bearer would receive a peak shock
load each step. However, a fairly constant load on the
shoulder is more comfortable and less fatiguing than a cyclic
shock load. By tuning the spring rate and the weight of the
load to the bearer’s stride, the shock loads on the bearer’s
shoulders can be greatly reduced. Figure 11.2 illustrates how
the shock loads occurring with a rigid pole can be reduced
with a properly designed flexible carrying pole.
11.2. Load on bearer vs
time with rigid and flexible
TFi = Transmissibility.
............. - --e
zsig:; w-d;::::::::::::
Time ---)
.......................... .:.:.:.:.:.:.
Using a
Using a
flexible pole
- -.
The shock loading can be reduced by stepping more
rapidly or by increasing the deflection of the pole. The pole
deflection can be increased by using a more flexible carrying
Bamboo is a natural composite material, and a typical
bamboo carrying stick has a spring rate of 24 N/cm (13.7 lb/
inX2 In other words, a force of 24 N deflects the carrying stick
1 cm. A person striding 180 steps per minute and carrying a
load of 54 kg (120 lb) will experience a shock loading only
one-third as great as if carrying the load at the same speed on
a rigid pole.
Once the bearer’s stride in steps per minute and the
weight of the load are known, the carrying pole can be
designed to a specific transmissibility of the shock load using
the graph in Figure 11.3, which shows the pole deflection,
required to secure a specific transmissibility of shock load
according to the bearer’s gait.
A person with a gait of 120 steps per minute who wishes
to reduce the transmissibility of shock load to one-fourth the
peak load will need a carrying pole with a deflection of 30 cm.
To obtain this condition and carry 80 kg (40 kg on each end
of the pole), the carrying pole must deflect 30 cm under a load
of 40-kg-a spring-rate of 13 N/cm (7.5 lb/in).
11.3. Transmissibility of
shock load vs gait.
As a rule, the driving frequency should be two to three
times the natural frequency of the pole and load for effective
reduction of the shock load. When the ratio of driving
frequency to natural frequency~ is less than 1.41, the system
will resonate and create a transmissibility greater than one.
2 1.1.2 Bicycles.It appears to be a paradox that a person can.
move himself and a machine (bicycle9 weighing lo-20 kg with
less energy than if he were moving on foot at the same speed.
An analysis by Tucker compared the efficiency of moving of
various animals, man, and transport devices by using a
dimensionless quantity IPi + WVI.3 Pi is the power input
commonly known as the metabolic rate, W is the weight of the
animal or human, and V is the velocity of the animal along a
level path.
When an active muscle shortens, it does mechanical work.
When it lengthens! work is done on the muscle.
Active muscles stretching as well as shortening during
locomotion are characteristics of walking and running in
humans and in other terrestrial bipeds and quadn.tpeds.
The necessity for muscle stretching seems to be associated
largely with the cyclic acceleration and deceleration of the
animal’s center of mass during running. The leg mluscles
shorten, accelerating the animal upward and forward;
later in the step cycle, the center of mass falls and the
active muscles are stretched as they slow its rate of descent
and forward motion. To begin a new cycle, the muscles
then shorten again. An alternate strategy for running
animals is to prevent active muscles and elastic structures
from stretching at all. This can be accomplished by means
of a mechanism that converts the downward velocity
component of the body’s center of mass at the end of one
step cycle to the upward component at the start of a n&w
cycle without either storing mechanical energy elastically
or degrading it to heat. The mechanism applies a force to
the center of mass at right angles to its direction of
A bicycle is such a mechanism. Muscle efficiency while
pedaling a bicycle is high-about
25%---because the active
muscles are not stretched as much while pedaling as they are
while walking or running. Furthermore, the wheels stabilize
the rider’s center of mass so that it does not move up and
down as when running ,or walking, but rather moves in a level
plane. Body mass is not lifted with each pedal stroke as it is
with ~e;ichstep while walking. The energy thus saved can be
,use,d by the bicyclist to propel himself and the bicycle
The fastest humans can run a mile in just under 4 minabout 24 ,km/h (15 mph). A bicycle, however, can reach a
speed of nearly 100 km/h (62 mph).
A bicycle used for transporting freight has larger axles,
stronger wheels, and a heavier frame than a touring bicycle.
Loads are usually carried in a pair of panniers on each side of
the rear wheel. Additional loads are sometimes balanced on
the handlebars or fixed to a carrier over the front wheel. A
load of up to 200 kg can be carried on a bicycle.
A tricycle suitable for transporting freight or passengers is
made by replacing one of the wheels of a bicycle with a bed
or seat and a pair of wheels set l-1.5 m aparr. In Asian
countries such as Bangladesh and Indonesia, a pedicab is
constructed by lengthening the frame and replacing the rear
wheel of the bicycle with a wide axle, two wheels, and a seat
with canopy. Two or more people sit facing the direction of
travel. The operator steers with handlebars.
In other
countries, such as Peru, a tricycle for freight and passengers
is crented by lengthening the frame and replacing the front
wheel with an axle, two wheels, and a box or platform (Fig.
11.4). The operator steers with a handlebar fastened to the
rear of the box.
Although multispeed gearshifts might prove advantageous for bicycl~es used for transport, those bicycles currently
used are primarily of a fixed gear ratio.
1I. 1.3 Wbee~barmosand handcarts. WheeltYarrows are
commonly used on farms because they can move cargo on
paths where two-wheel carts cannot go. Also, they can be
turned sharply in restricted areas. Pneumatic tires are
preferable to keep roiling resistance to a minimum. If the
wheel is steel-rimmed, it should be large in diameter-at least
50 cm-and the rim should be about 10 cm wide.
The European wheelbarrow (Fig. 1I .5) is operated by one
person and is designed to carry up to about 100 kg over short
distances. The Chinese wheelbarrow (Fig. 11.6) i,s designed
11.4. Tricycle with
passengers and cargo
11.5. European
11.6. Chinese wheelbarrow.
to carry about 250 kg (550 lb) over long distances, with one
man between the handles pulling against a strap, and, if
necessary, another person pushing at the rear. The Chinese
wheelbarrow is designed so the load is balanced on the large
wheel (nearly 1 m in diameter). The wheel is secured to tile
center of the wooden frame so that the weight on the handles
does not exceed 20 kg.’
The European wheelbarrow is constructed so that the
wheel, which is located in front, carries a little over half the
load.~ ,The operator lifts the remainder of the load by the
Since pneumatic tires have much less rolling
resistance than steel-rimmed tires, many European wheelbarrows are manufactured with small-diameter pneumatic tires
(instead of steel wheels For similar wheelbarrows) so that the
wheel can be set closer to the operator, thus carrying a greater
percentage of the load.
A steel wheel running on a steel rail has a very low
coefficient of friction. In the Philippines, passengers and farm
produce are transported on public railroad lines by trolleys
(called rail cars or skates in some countries), which are owned
and pushed by private entrepreneurs (Fig. 11.7). The trolley
consists of a wooden platform about 1.3 m square with a split
11.7. Rail car (Philippine
bamboo floor and a bench for passengers The platform rides
on four ball bearings. Four smaller ball bearings are mounted
underneath and ride against the inside of the rails to keep the
trolley on the track. The troiley is propelled by the operator
pushing off on one rail with one foot while standing on the
trolley with the other foot and pushing against a bar on the
rear of thk passenger bench. Normal speed is 15 km/h. A
piece of trucktire attached to the platfoml and trailing on the
rail serves as a brake. By stepping on the piece of tire, the
operator can bring the vehicle to a halt.
The trolley is lightweight, as it must be removed from the
track when a train approaches. Since the trolleys run on
single-track rail lines, unwritten rules of +&eroad have evolved
that require a lightly laden trolley to make way for an
approaching, heavier laden one; a trolley with young passengers must make way for one with older passengers; and a
trolley with male passengers must make way for female
passengers. Such a trolley can easily transport 0.5 t of grain
and several people from one village to another.
Monorails are used in some rough tropical areas to
transport ,bananas. The bananas are hung From carriers that
ride on the monorail on steel wheels mounted on antifriction
An operator pulls the train of bananas from
collect,ion depots on the plantation to a highway, where they
are loaded into trucks,
Some monorails are equipped with a carrier powered by
a S-hp engine and equipped with a seat so the operator can
11.2 Animaltransport
Much of the world’s produce is transported by animals.
(Several means of animal transport were discussed in Chapter
1.1 Where only trails exist, animal-borne goods must be
carried in packs cinched to the animals’ backs or in panniers.
The common large draft animals such as horses, mules,
donkeys, bullocks, water buffalo, and camels can pull much
greater loads than they can carry. Sleds and wheeled vehicles
are utilized where roads are available.
The dogsled and the horse sleigh are romantic, but carry
little or no farm produce. The sled important to agriculture
is the wooden sled used to haul loads over fields and roads
do- .,- ’&o the farm. A typical farm sied is 20 cm high, 180 cm
long, and 75 cm wide. The sled is low to the ground and is
very usefut for hauling heavy objects such as ,stones. In
Southeast Asia, sleds drawn by water buffalo are frequently
used to carry seedlings at transplanting time and small
threshers during harvest. Depending on the surface and slope
upon which the sled rides, it can carry up to 400 kg.
A wooden sled runner on a dry smooth stone surface has
a coefficient of sliding friction Cf.1of 0.38, while on snow or
ice fs is 0.035. If the sled runners have metal shoes, f, is 0.02.”
The’draft required to pull a sled is equal to fs times the gross
load of the sled. So a wooden sled with a gross weight of 200
kg, running on dry, smooth stones requires a draft of 0.38 x
200 kg = 76 kgf (745 N). On wet grass or a wet but firm
wetland field, the draft is less.
It is estimated that only 50% of India’s 600,000 villages are
connected y all-weather roads, and one-third of all Freight is
transported \ >y animal power. Of the 15 million animal-drawn
vehicles in India, 12 million are located in rural areas, where
work animals are kept primarily for plowing. IJsing these
animals for pulling carts, like the one in Figure 11.8, doubles
their usefulness and provides additional employyment for their
The large wheels and height of bed of the cart in Figure
11.8 allow the shoulder yoke to sit on the bullocks. The driver
11.8. Cart drawn by a pair
of bullocks (India).
Bed size
3.9 m
1.8 m
1 x 2.5 m
Ground-to-bed height
Wheel diameter
1.6 m
600 kg
sits astride the poles above the tongue between the two
animals. The driver’s proximity to the animals’ heads permits
him to control them with a short goad or whip, as well as
verbal commands.
The amount of draft required to pull a, whee!ed vehicle
can be calculated by multiplying the gross ‘axle weight by the
coefficient of rolling friction using the equation
D = f, x L
where D = required draft,
fr = coefficient of rolling friction, and
L = load
The equation assumes that the wheel bearings are in good
condition and well lubricated, that the load is being pulled on
a level surface, and that the force required to nccelemte the
load to the vehicle’s operating speed is not i~-&ded.
The coefficient of roiling friction Vd;ifZ according to the
type and size of t,ire and the surface being traversed (see Table
11.0. For example, a bullock cart with a gross load of I ,OGO
kg on two 4 x 36 steel-:iredwhe&
and on grass sod requires
a draft of 74 kgf (720 N, I63 lb) as shown by the equation
fr x L
D = 0.074 x 1,000 kg
D = 74 kgf
If the same cart were in loose sand, the required draft
would be 413 kgf (4050 N, 909 lb).
If all the weight of both the vehicle and load are carried
by the wheels and all wheels are the same size, the draft
required to pull the load is easily obtained by multiplying the
gross weight by the coefficient of rol ling fi-iciiron. If the wheels
are not the same size, drdft can be calcuiated by individually
calculating the draft required for the load carried by the front
wheels, and the load carried by the rear wheels, and summing
the two drafts.
The rolling resistance of a pneumatic tire consists of two
parts: the flexing of the tire carcass and the resistance of the
surface to deformation. Rolling resistance is caused primarily
by tire flexing on a paved surface, or by soil deformation on
soft ground. The draft of a vehicle equipped with pneumatic
tires can usually be reduced on a hard surface by inflating the
Table 11.1. Coefficients of rolling friction for steel wheels and pneumatic tires?
2.5 x 36 steel
4 x 36 steel
6 x 26 steel
6 x 48 steel
4 x 30 4-ply
4 x 36 4-ply
8.00 x 16 4-ply
7.50 x 10 4-ply
7.50 x 16 4-ply
7.50 x 28 4.~1~
7.50 x 36 4-ply
Load per
wheel in
lb (kN)
pressure in
‘psi (kPa)
1,000 (4.45)
1,000 (4.45)
1,000 (4.45)
1,500, (6.67)
1,000 (4.46)
1,000 (4.45)
1,000 (4.45)
1,500 (6.67)
1,500 (6.67)
1,500 (6.67)
1,500 (6.67)
36 (248)
36 (248)
20 (120)
20 (120)
20 (120)
16 (110)
16 (110)
16 (110)
Coefficient of rolling friction
tires to the upper limit of aliowable inflation pressure. When
operating on soft soil, the tires should be deflated to the lower
range of inflation pressure, or slightly underinflated.
To move a vehicle up a hill requires more draft than to
move it at the same speed on a horizontal surface. A slope
or incline is generally described as a “grade” such as “1:20” or
as a “percent” such as “5%.” Both nomenclatures describe a
hill by stating the units of vertical rise for 100 units of
horizontal distance. For example, a road with a 1:20 grade or
a 5% slope rises 5 m for every 100 m of horizontal distance.
In this example, the gross weight of the vehicle is actually
lifted 5 m for every 100 m the vehicle travels horizontally.
The increased draft required to move a vehicle up a slope
is proportional to the slope. A cart with a gross weight of
1,000 kg going up a 10% grade will require 100 kg more draft
(10% x 1.OOOkg = IO0 kg) thtn for t:ie horizonral.
To calculate the power to pull a vehicle up a hill, the t,otal
draft is equal to the draft to overcome rolling friction plus
the draft required by the slope of the hill. For example, if
the bullock cart described on page 283 is pulled up a 7%
grass sod slope at 3 km/h, the bullocks will need to expend
1.6 metric hp.
= [(draft overcoming rolling friction) +
(overcoming the hill)] x speed c 270
= [(.074 x 1,000 kgf) + (7% x 1,000 kgf)] x 3 km/h + 270
hp,,,,,, = (74 kgf + 70 kgf) x 3 km/h c 270 = 1.6 hp
Farm wagons have four wheels and are usually larger
than carts.. Since the weight of the load being transported is
supported totally by the wheels, none of the load is carried by
the animals drawing the wagon. Steering of farm wagons is
accomplished either by a fifth wheel or an automotive-type
steering mechanism. The fifth wheel-type of steering provides very sharp turning. The front axle is attached to a
horizontal disc or largk bearing, which is fastened by a pin to
a stat,ionary disc on the bottom of the wagon. To keep the
bottom of the wagon box at a reasonable level, however, it is
usually necessary to make the front wheels of smaller
diameter than the rear wheels, since the front wheels must
pass under the wagon box. Few farm wagons or carts are
equipped with springs. In many European countries, the law
requires that farm wagons be equipped with brakes. In the
rest of the world, such regulations dd not exist or are not
Most animal-.drawn wagons have some sort of
mechanical w-he& hrzke, while tractor-drawn wagons depend on the tractr?r f~jr &king.
Today, most farr:: wagons use pneumatic tires, since they
provide lower rolling resistance than steel-rimmed whects.
They also provide a softer ride for the fal~mer. W%gcr~;sare
frequently equipped with worn truck tires, which are quite
11.3 Tractors
Transportation is an important function of pedestrian and
farm tracters. In countries such as Pakisan. ~7 WAKER
as onethird of tractor hours are used for transport. -rile tractor is used
to pull a wagon or trailer fi!led with goods or people (Fig.
I1.9). Transportation provides the tractor oxvner with income
when the agricultural calendar does not require the tractor for
tillage, threshing, or fieldwork. -car this reason, t,ractcYfswith
high-speed road gears are preferred by owners. If a tractor is
used frequently on paved roads, the rear tire lugs develop
sharp edges because, as the tire squeezes from the load, some
rubber P.-ill be abraded from the lug, and the edges of the lugs
will remain sharp. A tractor that~ is used only in fields will
exhibit tires with rounded edges on the tire lugs.
11.9. Edestrian tractor and
11.10. Farm tractoi with
highway trailer hitch and
brake connections.
Some tractor manufacturers provide an air compressor
and air brake system as optional equipment. Another option
is a standard highway tiuck trailer coupling that enables
tractors to puil four-,&eel high-speed truck tmilers over local
roads to small villages (,Fig. 11.10). Because the hitch for
highway trailers is higher than the tractor axle, the tractor must
be properly weighted in front and accelerated with care.
Front-end hydraulic loaders and forklifts (Fig. 11.1 lo), or
platforms mounted on a tractor’s three-point hyd,raulic lift,
provide versatile means of transporting material for short distances. The front-end loader is usuaily equipped with a
buckrrt. Not only can the loader be raised and lowered, but
it can be t.ipped hydraulically. The bucket is normally used
for jobs such as moving manure or scooping grain, but it is also
utilized to move items as diverse as firewood, bags of feed,
concrete blocks, bags of cement, and stones. Other options
for the front-end hydraulic loader include grappling hooks fol
grasping and moving large round bales, comprersion tongs
for moving blocks of about eight smatl rectangular. bales, and
pairs of pallet forks fix moving boxes of fruit or produce such
as potato in the field.
By attaching a pair of $let forks to a small platform (100
x 150 cm) cjn the rear .?-point hitch, the farmer has a hydraulic
platform by which loads can be lifted from ground level to the
height of a ~.agon t:)ed or loading platform, Rear forks are
used to move Large round baies (Fig. 11.12), and the smell
ptatfon~i is used for moving bags of feed and cans of milk.
boost farm xactors tneet the ASAE standard for the 3-point
.hitch, which specifies that at a poim 2 ft (61 cm’) to the real
of the lower lift links, a farmer can expect a minimum lift force
of 1040 lb i4.6 kN).
Tr;*ilers are very useful,
since they can be turned very
sharply when hitched to a tractor. The weight on the trailer
-hit& and thus on the drive wheels of the tractor helps increase
11 .I 1. Front-end loader.
Illustration courtesy of Massey-Ferguson.
a bilsinass of Varity Corporation
11 .12. Large bale being
loxied onto rear forks.
drive wheel traction. Farm trailers normally have a aptcity
of d-10 t.
Tractor trailers are often designed for the bed to be lifted
at the front by the tractor’s jlyclradic system. sot! iat bulk loads
can be dumped from the rear. Specialized high-lift trailers for
hauling vegetables are made with 3 recrangular lifting mechanism so that the tilted bed can be lifted 3 m ( 10 ft )-enoiIgh
to reach over the high sides of highway trucks.
Farm wagons in North America and many other areas are
usually purchased as two climponents-l-L!nlling
gear and
wagon box. The running 7 gear consists only of the axles,
wheels, and fi2me. The wagon box is either 3 covered forage
box for towing behind ;1 field forage harvester, ;I flatbed for
hand stacking !,:l,leci hay or apple crates, or a box with a
perforated floe-?rfor forced-air drying of peanuts or grass seeti
crops. If a farmer expects to he hauling very heavy loads. or
to be operating on soft soil. a higher capacity running gear
with large tires will be selected. To provide adequate
flotation, yet keep tire diameter from becoming excessive,
twin axles fitted with a walking beam are used as the rear axle.
They are then positioned to c3rr-y most of the load. The
walking bean axle provides good support on uneven ground
(Fig. 11.l.?). ‘Tires of dqu;ite
size must he used on a wagon
on 3 soft field to ;>revent it from bogging down.
11.33. Forage wagon with
walking beam tandem axle.
Illustration courtesy of Gehl Company
11.14. Feed-mixingwagon.
Illustration courtesy of Gehl Company
Several types of specialized wagons and trailers are
available. Automatic bale-loading wagons can pick up and
automatically stack hay or straw bales. Feed-mixer wagons
with electronic weigh cells placed between the running gear
and mixer box facilitate mixing various feed (Fig. 11.14).
Grain boxes with sloping sides so the box will empty clean11
when a bottom port is opened are used to haul grain from i
combine to a dryer or storage area. Boxes with sloping slides
and a center conveyor belt transport root crops such as
potato, red beet, and sugar beet. Some specialized trailers,
such as the automatic bale-loaders, d.o not fit onto separate
running gear. Their axles and wheels are an integral part of
the whole machine.
1. Campbell 0 F (1984)The ergometrics of a bamboo carrying stick. Cornell
University. (unpubi.)
2. Lakkad S C, Pate1J M (1981) Mechanical properties of bamboo, a natural
composite. Fibre Sci. Technol. 14(1980-81):319-322.
3. Tucker V A (1975) The energetic t?ost of moving about. Am. Sci. 63:413419.
4. Ibid., pp. 417-418.
S.~Hoffen HJ_ Bit &ski I? (1953) small farm implements. FAO Dev. Pap. 32.
Rome, Italy.
6. Baumeister ‘I, Marks L S, eds. (196:; tia.n.dard hau&~~~ok for mchrnic ;:I
7th ed. McGraw-Hill Book Co., New York. p. 3-39.
7. Ramaswamy N S, Narasimhan C L (1984) India’s .mimaIdrawn vehicles,
Indian Institute of Management, Bangalore.
8. McKibben E G, Davidson J B (1939) Transport wheels for agricultural
machines. Agric. Eng. 20(12):471.
Barweil I J, Edmonds G A, Howe J S G F, DeVeen J (1985) Rural transport
in developing countries. Intermediate Technology Publkations, Ltd., London.
Hathway G (1978) Appropriate technology in rurdl development: vehicles
designed for on and off fame operations. Transportation Department, World
Bank, Washington, D.C.
Hathway G (19%) Low-ca.t vehicles. fntemrediate Technology Pubiications, Ltd., London.
McKibben E G, Hull D 0 (1940) Tmnsport wheels for agriculturdl machines;
soil penetration tesEj as a means of predicting roiling resistance. Agric. Eng.
Whin F R, Wilson D G (1982) Bicycling science.
Cambridge, Massachusetts.
2d ed.
MIT Press,
Wooley J C, Jones M M (1925) The draft of farm wagons as affected by height
of wheel and width of tire. Univ. Missouri Bull. 237.
12 Social
conse uences
When mechanization is introduced in agriculture. skep&cs
often ask, “Doesn’t mechanization make the ri:h richer and
the poor poorer?’ The question has some justification, for
machinery can indeed replace humans in some agricultural
jobs. Other appropriate questions1 however, can also be
posed. “Does mechanization he!p produce more food and fiber?” “Does mechanization alleviate toil and improve the
quality of the farmer’s life?”
Disagreement concerning the desirability of agricultural
mechanization frequent!y arises because the machinery itself
is blamed for unequal distribution of the crop yield increase.
Critics point out that even when mechanization increases the
output of the agricultural system, the laborers do not receive
a proportionate share of the surplus. Unfortunately, this is
often true. In socialiy stratified countries, where land tenure
and inequality are the norm, technologicai inputs such as
agricultural machinery are unlikely to stimulate abrupt social
change. Agriculturists and engmeers have often succeeded in
increasing food production in LDCs by introducing modern
Social and political
varieties, methods, and machinery.
scientists, however, have been largely unsuccessful in improving the equity of distribution. It is difficult for a foreigner
to advise an old and stable society to revise its social structure.
Social change within a country must develop from its own
12.1 Mechanization
and agrhltural
In many agricultural countries, nonmechanized agriculture
prcvides some employment to persons who in indlustrial
nations would be receiving food stamps or would be living on
This method of
the dole because of lack of income.
production involves high labor input per unit of food produced and very low wages for the workers. It cannot be
agricultural system
depends on both its notion of social justice and its agrociimatic
A study examining the changes in employment, production, and income resulting from small rice farm mechanization
in the Philippines, Thailand, and Indonesia revealed that
reduced labor requirements during land
preparation. Total labor output, was higher during the dry
season than the wet season, except for farms irrigated by
gmvity systems (Fig. 12.1).
Figure 12.1 illustrates that in both the wet and dry seasons,
labor days per hectare of rice decreased. The decrease was
most apparent during land preparation and threshing. These
tasks, of course, are normally the first to be mechanized. A
significant difference in the am(:i : of hired labor between
12.1. Labor for rice
production in two Philippine
NM = nonmechanized,
PM = partially mechanized.
good or bad, since a country’s
Labor%sebtmr &a)
Wet seaeon
mechanized and nonmechanized farms was not apparent.
However, permanent labor and seasonal hired labor were
used differently. The major reduction of labor benefited the
farmer’s family.’ Data from West Jaya and South Sulawesi,
In gelieral, labor
Indonesia, revealed the same trend.
requirements per hectare of rice declined, hired labor increased on most mechanized farms, and the major reduction
of labor on mechanized farms was enjoyed by the farmer and
the farm fami1y.j
Another Philippine study used 1978 data to calculate the
effect on employment from a 1% increase in consumer
spending for rice.’ The study predicted that a 1% rise ir.
consumer spending for rice would increase employment in
the Philippines by 23,000 workers using full mechaniztion
under nonirrigated conditions, and by 53,000 workers if a low
level of mechanization were used under pump-irrigated
conditions. The increase in jobs would affect not only farm
labor, but (more importantly) labor in the nonagricultural
sector. The projected effect of the t)rpe of threshing is shown
in Table 12.1; manual threshing produces 22% more work in
agriculture than the use of portable mechanical threshers
does. In the nonagricultural sector, however, the portaM,mechanical thresher produces 2% more work than matlual
threshing. I:1 total, under the condition of a 1% increase in rice
production, manual threshing requires more hours of labor
than mechanical threshing, but the increase is prill?arily in the
agricultural (not nonagricultural) sector.’
12.2 ~Mechanization
and crop yield
In a rice-growing area in Central Luzon in the Philippines, a
study was made to investigate the differences in inputs,
cropping intensity, and yield for nonmechanized, partially
Table 12.1. Employment implications of threshing method for a 1%
increase in rice production in the Phllippines.6
sector (direct) sector (indirect)
Manual threshing,
1000 labor-yr
Mechanical threshing,
1000 labor-yr
Difference (%)
mechanized, and Fully ; I:ti,chanized farms in nonirrigated and
irrigated areas. The irrigated areas were classified into
rainfed, pump-irrigated, and gmvity-irrigated. The classes of
mechanization were based on the type of power utilized for
land pry. + ,-&on in both the wet and dry seasons. Nonmechaniz4 farms used cimit animals for land preparation in
both seasons, while ful!y mechanized farms used pedestrian
tractors or fatm tractors in both seasons. The farms using a
combination of animal and mechanical pow-er were classified
as pdrhlly
The study revealed that irrigation was :he major determinant of yie!d and cropping intensity, and thal there was no
evidence of a ,yield effect directly attributable to mechanization (Table 12.2). These findings support similar studies of
nonmarginal agricultural product.ion systems (that is, systems
that do not have a narrow time frame during which tillage,
seeding, or some other element of the agrisultural calendar
must be accomplished if a crop is to be produced.)
Mechanization shortens the turnaround interval between
crops. Turnaround time for a mechanized rice farm vs a
nonmechanized farm is substantially reduced because the:
farmers control irrigation by utilizing their own wells ard
pumps. For community gravity irrigation systems, little or no
difference in turnaround time exists between mechanized and
nonmechanizei farms. The cropping sequence is determined
by irrigation water, which becomes available to both mechanized and nonmechanized farms at the same time.
In areas where the growing season is limit~ed, mechanization can inclrdse crop yield. For example, in the U.S. corn belt
there is an optimal period of a few weeks in which to plant
maize. If planting cannot be accomplished during this time
frame, yield reduction will result. For this reason, 8- or 12-row
Table 12.2. Rice productivity in selected villages in Guimba and Cabanatuan, Nueva Ecija,
Philippines, 1979 wet season.8
Rough rice yield
In kg/ha
In kg/kg of nitrogen
In kg18 h of labor
Partially mechanized
maize planters are often preferable
Timeliness is more important
irrigated regions. Capacity utilization,
over a large area to lower costs, is
with timeliness.
to 4- or Grow units.
in nonirrigated than in
when a machine is used
frequently incompatible
12.3 Mechanization
and farm income
In sub-Saharan Africa, a comparative study of h,and-hoe
households and farm households mechanized by the introduction of animal traction revealed that the latter households
had net returns higher by 2-5 times.” However, the farms
animal traction were typically larger and had more
household members than the hoe-fanns, so the differences
were not qlaite as large on the basis of revenue per hectare or
per capita.
A study in the Philippines where three classes of rice farm
animal and tractor, and tractorwere compared revealed that mechanization significantly
affected income on large (2.5 ha and over> farms. An
economy of scale was noted in the use of machines on larger
farIns.“’ Income data for the classes of farms in the study are
shown in Table 12.3.
12.4 .Affordable
A farmer cannot purchase farm :ndchinery to improve his
quality of life if conditions be;ronci his control such as
governmental policies and tr:-ti I L>port conditions keep crop
prices low. A revealing comparison of the clegree of mecha-
Table 12.3. Mean household and per capita income by farm size, mechanization class, and season
in 8 villages of Cabanatuan and Guimba, Nueva Ecija, 1979 wet season and 1980 dry season.”
Farm size class
(animal) -Wet
Below 1.OOha
Household income
Per capita income
Household income
Per capita income
2.50 ha and larger
Household income
-_Per capita income
----A Income ( P)
nization in various rice-growing Asian countries is obtained
by comparing costs of tractors, draft animals, and nitrogen
fertilizer in terms of tons of rough rice required to purchase
those items (see Table 12.4). A small pedestrian tractor, for
example, costs only 3 t of t,ough rice for theJapanese farmer,
but 28 t for the Indonesian farmer. In the Republic of Korea,
a farmer needs to sell 1,2 kg of rough rice to purchase 1 kg
of nitrogen, while the Thai farmer must sell 4.8 kg of rice. ’
Table 12.5 indicates the number of rice crops a farmer
must sell to purchase mechanical power or draft animals. This
table reflects differences in average farm size and rice yield,
as well as rice prices in the various Asian countries. It also
illustrates the fact that the average rice farmer in India,
Indonesia, or Nepal cannot afford a tractor.
The lack of high yie!,ds and agricultural mechanization in
many Asian countries is due to small farm incomes rather than
to small farms.
Table 12.4. Cost of mechanical power, draft animals, and fertilizer in tone of rough ricePI
No. of crops of rough rice
India Indonesia Japan Nepal Pakist& Philippines Rep. Korea Thailand
8-hp pedestrain
45hp farm tractor
1,000 I diesel fuel
Draft cattle, 1
Water buffalo, 1
Nitrogen fert. 1 kg
55.4c 150.0
'5-7 hp. b12hp. ‘35hp.
51 .Od
"30-60 hp. * 30-55hp.
Table 12.5. Number of crops of rough rice from an average size farm with average yield needed tc
purchase tractors and draft animals in selected Asian countries.‘3
No. of crops of rough rice
India Indonesia Japan Nepal Pakistan Philippines Rep. Korea Thailand
8-hp pedestrain
45-hp farm tractor
Draft cattle, 1
Water buffalo, 1
b12hp. ’ 35 hp. d30-60hp. e 30-55hp.
The problem of affordable machinery can also be seen in
Japan, Western Europe, and the U.S. High farm prices have
provided Japanese farmers with greater tractor power per unit
of cultivated land than farmers in any other major country.
Westein Europe’s high farm subsidies have resulted in a
proliferation of specialized agricultural machines and a tractor
power intensity greater than that of the U.S., though less than
that of Japan. The U.S. hasplarge farm tractors for large farms,
but horsepower per cultivated area is less than that of Western
Europe because the prices U.S. farmers receive for their
products are lower.
12.5 Mechanization
and quality of life
Women and children who work in the fields are employed,
but at what cost? Children in the fields are not in school and
may be condemned to lives of menial labor. Women age
prematurely by laboring in the fields as well as performing
the housework their societies demand of them. Is the use of
machinery to alleviate such conditions socially undesirable?
Young people living on farms in LDCs are no longer cut
off from other parts of the world. Schools, radio, television,
and cassette players remind them that life can be more than
back-breaking work and drudgery. With this in mind, they
go to Lima, Manila, Dhaka, and other cities and add to urban
Farm mechanization in LDCs is inevitable.
As other
varieties, fertilization, pest control,
prices--of the agricultural production system evolve, so will
mechanization. In one area it will be a change from the hoe
to the animal- or tractor-drawn plow. In another it will be froni
a water buffalo to a pedestrian tractor. In still another it will
be from 2-wheel- to 4-wheel-drive farm tractors and 4-row to
I.&row planters.
Agricultural mechanization helps farm
families reduce their hours of hard labor or enlarge their scope
of farming. These desirable goals on the part of the farmer,
however, may not always coincide with government pdlicies
to put !andless laborers to work. A farmer may be willing to
buy a machine to reduce drudgery for his fainily, but not for
hired labor,
Economists may have a measurement problem when
attempting to evaluate the overal! benefit of mechanization,
since one of the main benefits is reduced drudgery. If benefits
are high, and economic analysis fails to include them, the
analysis may wrongly conclude that the farmer made a poor
In temperate zones, storeowners and office
workers can drive to work in automobiles ‘with power
steering. They work in air-conditioned comfort in summer
and heated offices in winter. Why should the farm family fin
the same region not purchase a tractor with power steering
and an enclosed cab equipped with air-conditioning and
heating for their “office on wheels”?
The social consequences of mechanization are complex.
What appear ‘to be perverse decisions by farmers to use
inappropriate machines may well be the result of skewed
government policies such as overvalued exchange rates,
subsidized credit, and excessive tariff protection. Misplaced
investment in agricultural machinery occurs in both developed and developing countries.
In general, mechanization reduces employment in agriculture, although some of the displaced workers will find
employment in factories producing the new machines and
agricultural technology.
Where the growing season is limited and a labor shortage
is inevitable, or where specific problems such as difficult
tillage exist, mechanization can increase yields. However,
even on intensively cultivated farms blessed with good soil,
water, growing conditions, and labor, mechanization will not
necessarily increase crop yield.
An economy of scale appears to exist in that larger farms
can increase income by increasing mechanization-up
to a
point. Smaller farms, on the other hand, may be able to obtain
some of the economy of scale by utilizing custom hire
Throughout the 20th century, the mechanization of agriAs people seek less
culture has continued to develop.
arduous lives and the dema,nd for food grows, mechanization
will play an increasingly important role in agriculture.
1. Duff’JB (1986)Someconsequences
of agriculturalmechanizationin the
Philippines,Thailand,and Indonesia.Pages59-84in Smailfarm equipment
for developingcountries. InremationalRice ResearchInstitute, P.O. Box
2. Ibid., p. 69.
3. Ibid., p, 71.
4. Ahammed C S, Herdt R W (1985) A general equilibrium analysis of the
effects of rice mechanization in the Philippines. Modeiling the impact of
small farm mechanization. Philippine Institute for Development Studies
Monog. Ser. 5. p. 38-68. Manila.
5. Duff J B (1986) Changes in small-farm rice threshing technology in
Thailand and the Philippines. IRRI Res. Pap. Ser. 120.
6. Ibid., p. 11.
7. Shields D (1985) The impact of mechanization on agricultural production
in selected villages of Nueva Ecija. J. Philipp. Dev. 12(1):182-197.
8. Ibid., p. 193.
9. Pingali P, Bigot Y, Binswager H P (1987) AgricukuraI mechanization and
tire evolution of farming systems in sub-Saharan Africa. Johns Hopkins
University Press, Ba!timore, Madison. p. 110-l 11.
10. Lim P C (1985) Effects of agricultural mechanization on farm income
patterns. J. Philipp. Dev. 12(1):198-206.
11. Ibid., p. 205.
12. Gee-Clough D (1985) Affordable technology. FFTC Extension Bull, 222.
13. Ibid., p. 24.
Boyce J K, Hartmann B (1981) Hunger in a fertile land. Food and Agriculture
Organization of the United Nations, Rome. p. 32-35.
Herdt R W (1983) Perspective issues and evidence on rice farm mechanization in developing countries. Pages 111-147 inFarm mechanization in Asia.
Asian Productivity Organization, Tokyo.
Herdt R W, Palacpac A C (19831 World rice facts and trends. International
Rice Research Institute, P.O. Box 933, Manila, Philippines.
Stavis B (1978) The politics of agricultural mechanization in China. Cornell
University Press, Ithaca, NY.
13 Machinery
Before purchasing an agricuhural machine, it is prudent to
determine its economic viability. Frequently, owners of costly
Farm machinery consider renting the equipment to their
neighbors to help offset the expense. Knowing the fixed and
variable costs of machinery used for custom work is necessary
prior to quoting rental rates. This chapter describes how to
estimate machine capacity, area worked, available rime, fixed
costs, and variable costs.
13.1 Esthating
:ost of field
-4 machine’s cost per hour worked is greatly influenced by its
usage. The annual hours of use of some tractors can be
determined by reading the hour meter. For most machines,
however, the annual hours of use must be calculated by
dividing the area worked by the machine’s ejjjectiuecupacity
(EC). Effective capacity equals the theoretical capacity
multiplied by the field efficiency. Theoretical capacity is the
machine’s capacity, working 1S.M of the time. Field efficiency accounts for efficiency lost while attaching wagons,
turning, filling fertilizer hoppers, emptying grain tanks, slowing down over rough terrain, stopping for tea break, and so
Width(m) x speed (km/h) x
field efficiency (decimal)
EC (ha/h) =
EC (acres/h) =
With (ft) x speed (mph) x.
field efficiency (decimal)
For example, a 1.7-m reaper traveling at 5 km/h at a field
efficiency of 60% has an EC of
1.7m x 5kmlh x 0.60
= 0.5 ha/h
Normal speeds and efficiencies of field machinery are
shown in Table 13.1.
Table 13.1. Field machinery data.
Anhydrous ammonta
Baler with engine
Baler, PTO
Baler, large round
Chisel plow
Combine, PTO
Combine, self-propelied
Cultivators, seeder,
Cultivator, field
Cultivator, row crop
Disk plow
Fertilizer equipment
Flail harvester
Forage blower
Forage harvester,
Forage harvester,
Grain drill
Harrow, single disk
Harrow, tandem disk
Harrow, heavy tandem
Harrow, spring-tooth
Harrow, spike-tooth
Land plane
Land roller
Loader, front-end
Estimated Repair
life (h)
Depreciation Field
group efficiency
.60 - .75
.60 - .85
.60 - .85
.60 - .85
.70 - .90
.85 - .80
.65 - .80
.70 - 530
.80 - .90
.70 - .90
.70 - .90
.70 - .90
.60 - .75
.50 - .75
.50 - .75
.50 - .85
.50 - .85
.70 - .90
.70 - .90
.70 - .90
.70 - .90
.70 - .90
.70 - .90
Table 13.1. continued.
Maize head
Maize picker
Maize planter
Manure spreader, beaters
Manure spreader, flail
Manure spreader, liquid
Middle breaker
Moldboard plow
Mower, cutterbar
Mower, flail
(horizontal blade)
Potato harvester
Rake, side delivery
Rod weeder
Rotary hoe
Standby power unit
Sprayer, mounted
Sprayer, self-propelled
Swather, self-propelled
Stalk cutter
Tractor, pedestrian
Tractor, 2-wheel drive
Tractor, 4-wheel drive
Tractor, tracklayer
Truck, farm
Truck, pickup
Wagon box
Estimated Repair Depreciation Field
life (h)
.60 - .80
.50 - .85
.60 - .90
.60 - .90
.80 - .9d
.70 - .90
.70 -.90
.75 - .85
.80 - .90
.80 - .90
55 - .85
.60 - .80
.70 - .90
.73 - .90
.70 - .85
.50 - .80
50 - .80
.70 - .90
.60 - .85
.70 - .90
Effective capacity is used to calculate a machine’s annual
hours of use. For example, if a farmer uses a reaper with an
EC of 0.5 ha/h to cut 40 ha of rice per year, the annual hours
of use = 40 ha + 0.5 ha/h = 80 Nyr. For crops such as grasses
that are harvested several times per year, or for a field plowed
several times per year, the area worked by the machine is the
area traversed by the machine in 1 yr. For exampl,e, if a mower
cuts a 20-ha field of alfalfa 3 times a year, the mower cuts 60
The total cost of operating an agricultural machine consists of fixed costs (sometimes called ownership costs> and
costs (sometimes called operanonal costs). The
variable costs-fuel and lubrication, repairs, labor-depend
on the use of the machine, while fixed costs-depreciation,
interest on investment, insurance, shelter-are independent
of machine usage.
Depreciation occurs as new technology and practices
make older machines less desirable. As machines age, the
likelihood of breakdown increases. Depreciation can be
calculated by trade-in value. The actual value of a machine
(and thus its depreciation) is unknown until it is sold secondhand or abandoned. Depreciation can usually be estimated
with general knowledge of used equipment prices.’ Farm
machines do not all depreciate at the same rate. To help
estimate depreciation, the machines are classified into four
general depreciation groups: A, B, C, and D. Group A
machines depreciate at the slowest rate and Group D, the
fastest. A hay baler (Group D1 depreciates faster than a tractor
(Group A).
Based on the interpretation cf such data,* Table 13.2 lists
the average values for 4 groups of machines up to 15 yr old.
The estimated values are in U.S. dollars per $1,000 of initial list
Insurance, shelter for the machine, and interest on the
investment are the remaining fured costs. Interest is a
consideration regardless of whether or not the farmer borrows
money from the bank. Even if the farmer pays cash for the
machine, interest is an expense in that the capital could
otherwise be drawing interest on the money. In Table 13.3,
interest at lo%, insurance, and shelter are lumped together as
an annual cost equal to 12% of the depreciated value of the
machine. In Table 13.4, interest at 20%, insurance, and shelter
are lumped together as an annual cost equal to 22% of the
depreciated value of the machine.
Table 13.2. On-farm value of agricultural machines in U.S. dollars per $1,000 of initlai list price.
On-farm value (US$) at a given age in yr
9 10 11
212 195
116 102
108 96
101 90
Table 13.3. Average annual fixed cost In U.S. dollars per $1 ,ooOof initial list price @ 12% of average
Cost ($) at a given age in yr
a Based on depreciation from Table 13.2 plus 12% (10% interest + 1.5% shelter + 0.5% insurance) of the average value
during the year. It is assumedthat a new machine is purchased at 10% below list price.
Table 13.4. Average annual fixed cost in U.S. dollars per $1 ,CHJO
of initial list price @ 22% of average
Cost ($) at a given age in yr
a Based on depreciation from Table 13.2 plus 22% (20% interest + 1.5% shelter + 0.5% insurance) of the average value
during the year. It is assumed that a new machine is purchased at 10% below list price.
Depreciation is added to the other fiied costs for four
machinery groups and listed in Table 13.3 as accumulated
fured costs per $1,000 of initial list price up to 15 yr. The prices
cited in Table 13.3 reflect a 10% discount from the initial list
price, since most agricultural machines are not sold at
advertised retail prices. For example, it is assumed that a
machine in Group A with a list price of $1,000 was purchased
for $900 at a 10% discount. One year later the machine had
depreciated to a value of $626 (see Table 13.2). During its first
year, therefore, the machine’s average value was $763. That
is, it was worth $900 brand new and $626 at the end of the
year, so its average value during the year was $763. The total
fixed cost for the machine at the end of the first year is
computed as follows:
First year depreciation = $900 - $626
= $274
First’year interest, shelter, insurance = 12% x $763 =
Accumulated total fixed cost
= $366
Table 13.3 was compiled using the above calculations. It
assumes an interest rate of 10%; Table 13.4 assumes 20%.
Fuel costs are probably the simplest variable costs to
compute. Most farmers keep their fuel receipts. Tractor fuel
consumption can be estimated from the following equations,
which are based on average varying power and fuel consumption runs from Nebraska Tractor Test reports.
Average fuel consumption can be estimated?
Gasoline (liters/h) = 0.227 x maximum PTO hp
= 0.166 x maximum PTO hp
Diesel (liters/h)
LPG (liters/h)
= 0.272 x maximum PTO hp
Gasoline (US gal/h) = 0.060 x maximum PTO hp
Diesel (US gal/h) = 0.044 x maximum PTO hp
LPG (US gal/h) = 0.072 x maximum PTO hp
The above estimates are for average fuel consumption per
hour. To estimate fuel consumption under maximu;n power
conditions such as heavy plowing, multiply the above estimates by 1.5. For example, if a lOO-hp diesei tractor consumes
an average of 17 liters/h, it uses 1.5 times the average under
maximum power conditions, or 25 liters/h.
Oil, grease, and filters are lumped together under lubrication, which averages 15% the fuel cost. Lubrication is
considered in the cost estimates by using the following
Fuel and lubrication cost = _
max PTO hp x _
x $/liter = $-/h
The factors are 0.261 for gasoline, 0.191 for diesel, and
0.313 for LPG. Factors for U.S. gallons are listed on the English
unit worksheets.
Repair costs are highly variable and depend largely on the
quality of machinery management. The terrain, soil, and type
of crop also dramatically affect repair costs. All variable costs
depend on the total hour; of machine use. Agricultural field
machines are classified into seven groups for estimating repair
COSts.‘~ The estimated life and repair groups for various
machines are listed in Trible 13.1. The repair curves (Figs.
13.1-13.7) provide estimates of repair costs at any point in the
life of a machine. The costs are shown as cumulative costs,
that is, the total repair costs from the day the machine was
delivered from the factory. The curves provide repair cost
13.1. Accumulated ccst of
repairs for repair group I.
estimates for farmers who have not developed their own
repair cost guides. The repair cost equations on which the
curves are based were developed from surveys in the midwestern US5
Figures 13.1-13.7 differ primarily in the rate of repair cost
increase in relation to cumulative hours of use.
If a repair group recommended in Table 13.1 does not
seem to fit a situation, another repair curve may be used. For
example, if the.recommended repair curve, repair group 3,
for a self-propelled combine seems too low, the estimated
repair cost can be increased by using a steeper curve, such as
repair group 4. The estimated repair cust can also be altered
by changing the estimated hours of life of the machine. Increasing the estimated hours of life will decrease the repair
cost; decreasing the estimated hours of life will increase the
estimated repair cost. If operators are not properly trained in
the use of machinery, if maintenance is poor, or if spare parts
are difficult to obtain, it is a good idea to lower the estimated
hours of life in order to increase hourly,repair costs. This is
often the case in LDCs.
The cost of operating .a machine can be estimated by
following the steps in the ~worksheet for metric units (Table
13.5) or that for English units (Table 13.6).
12OGU. life
0 II-
Total hours
Accumutated repairs (WlOOO ILP)
Total hours
ILP= 1.2 x (100 I houwestimated
hours life)'.s
13.2. Accumulated cost of repairs
for repair group 2.
13.3. Accumulated cost of repairs
for repair group 3.
Accumulated repairs ($i$lOOO ILo!
II -25h
Repair $/$lOOO ILP- 0.96x(100
x houwsstimated
hours Me)"
(.$%lOOO ILP)
Total hours
Repair$/$lOOO ILP- 1.27 x (100 x hoursleslimated
hours liie)'.4
13.4. Accumulated cost of
repairs for repair group 4.
13.5. Accumulated cost af
repairs for rapair group 5.
Total hours
ILP= 1.59 x (100 x hourskslimated
lwurs life)"
Total hours
Repair$/$lOOO ILP= 1.91 x (100 x hourskstimatsd
13.6. Accumulated cost of repairs
for repair group 6 (above).
Accumulated repairs($/$lOOO
hours life)"
13.7. Accumulated cost of repairs
for repair group 7 (below).
Total hours
ILP= 3.01 x (100 Y hours/estimated
hours lile)'-3
Table 135
:’ Machine
Field machinery
cost worksheet,
metric units.
New machine
initial list price
Estimated life
:: (2)
Hectares to work per year
Field speed
Width of effective swath
Field efficiency (your value or estimate from Table 13.1)
Effective capacity = (line 2) x (line 3) x (line 4) + 10
= i 10
(6) Annual hours of operation = yline 1) c (ine 5) E
(7) Expected age at trade-in
(6) Average annual fixed cost per $1000 Initial list price (ilp)
Use Table 13.3 (10% interest) or Table 13.4 (20% interest)
(9) Average annual fixed cost = (line 6) x (ilp/lOOO)
= ~
___ /I 000
(10) Fixed cost per hectare = line 9 + Iin: 1 = $ +
(11) Fixed cost per hour = line 9 + line 6 = $ ___
Repairs Age and hours on machine purchased by you
(12) Total accumulated repair hours at trade-in = line 6 x line 7
h/yr x __yr
(13) Repair cost factor from appropriate repair group (from Figures 13.1-13.7)
(14) Accumulated repair cost = ilp + 1000 x line 13
.(15) Annual average repair cost”= line ,4++‘i”,“,“=
$ __
+ yr
(16) Average repair cost per hectare = line 15 + line 1 =
(17) Average repair cost per hour = line 15 + line 6 =
Fuel and lube
(16) Fuel and lube = tractor or engine hp x F A L factorb x fuel cost
= ---hp
x ,.--F
8 L factor x $ ___ /liter
(19) Labor cost = number of operators x hourly rate = ____,_ x $--Ih
Tractor cost for towed implement
(20) Tractor hourly cost
Total operating costs:
(21) Operating cost per hour = repairs (17) + fuel (16) + labor (19) + tractor (20)
= ---_-- .-I_
+(22) Operating cost per ha = line 21 + Tine 5 =
(23) Total cost per hour = operating cost (line 21) + fixed cost (line 11)
=$ -Ih
+ $ -Jh
(24) Tota! cost per hectare = operating cost (line 22) + fixed cost (line IO)
= $ ---/ha
+ $ -/ha
“Obtain from Table 13.1 Field machinery data.
DFueland lube factor: gasoline = 0.261, diesel = 0.191, LPG = 0.313.
_ /$I 000 ilp
11000 ilp
= ---..=
= ..I__
= .-S----/h
= __-$
-Table 13.6. Field machinery
cost worksheet,
Engllsh units.
New machine
initial list price
Estimated lie
Acres to work per year
Field speed
Width of effective swath
Field efficiency (your value or estimate from Table 13.1)
Effective capacity = (line 2) x (line 3) x (line4) .+ 8.25
= __-+
(6) Annual hours of operation = ‘;tine 1) + (ine 5) = -.
+ __
(7) Expected age at trade-in
(8) Average annual fixed cost per $1000 initial list price (ilp)
Use Table 13.3 (10% interest) or Table 13.4 (20% interest)
(9) Average annual fixed cost = (line 8) x (ilp/lOOO)
= __/la00
(10) Fixed cost per acre = line 9 + line lx= $
(11) Fixed cost per hour = line 9 + line 6 = $
Repairs Age and hours on machine purchased by you
(12) Total acrumulated repair hours at trade-in = line 6 x line 7
= -hlyr x __
(13) Repair cost factor from appropriate repair group (from Figures t3.f<7)
(14) Accumulated repair cost = ilp + 1000 x line 13
x $--* 1,000 x __
(15) Annual average repair cost = line 14 + line 7 = $
1 -_(16) Average repair cost per acre = line 15 + line 1 = __
(17) Average repair cost per hour = line 15 t line 6 =
Fuel and lube
(18) Fuel and lube = tractor or engine hp x F 8 L factor” x fuel cost
F & L factor x $ ___/US gal
= -.hp
x i
(19) Labor cost = number of operators x hourly rate = ___
x $Tractor cost for towed implement
(20) Tractor hourly cost
Total operating costs:
(21) Operating cost per hour = repairs (17) + fuel (13) + labor (19) + tractor (20)
(22) Operating cost per acre L lina
+ line 5 =+
= -__
= _.-:
.- h
/$I 000 ilp
II 000 ilp
= -._
(23) Total cost per hour = operating cost (line 21) + fixed cost (line 11)
=$ p/h+$
(24) Total cost per acre = operating cost (line 22) + Eed cost (line 10)
= $ -...-.Jac
+ 9 -lac
Obtain from Table 13.1 Field machinery data.
“Fuel and lube factor: gasoline = 0.069. diesel = 0.050, LPG = 0.083.
= -t--/h
X3.2 Multipurpose
To some extent, a machine such as a combine is multipurpose;
with only a change of the header and some adjustments to
cylinder speed and concave clearances, the combine can be
changed from a machine to harvest small grain to one that can
harvest maize. Farmers have generally accepted this type of
flexibility in a machine.
Engineers and economists have pursued the goal of
developing a basic machine to which most of a farmer’s
implements can be added. For the engineer, the tool-carrier
concept holds forth the promise of an integrated line of
implements designed to fit a common tool carrier and thus
reduce the number of individual parts that must be designed,
manufactured, and carried in stock. For the economist, the
tool carrier concept has the promise of the farmer purchasing
fewer individual machines, thus investing less capital in
agricultural equipment. Although the goal has been pursued
for at least 50 yr, the concept of a common tool carrier instead
of individual machines has not been well accepted by farmers.
The farm tractor is used as a tool carrier. Because of the
world standard three-point hitch and PTO, implements from
many manufacturers can be attached to a farm tractor qui,ckly
and easily. The ease and the rapidity of attaching implements
make the farm tractor a tool carrier for the simpler implements. However, if there is need for many hours of work for
a particular implement, the tendency is to use a specialized,
self-propelled machine. For example, to cut a haycrop, a
mower can be attached to a tractor or a mower-conditioner
pulled by a tractor; however, if a large amount of mowing is
required, the farmer in many markets will probably purchase
a’self-propelled mower-conditioner or windrower.
In the U.S. in the 194Os, Minneapolis MolineTM developed
and marketed a self-propelled tractor chassis on which fitted
a grain combine, maize picker, maize picker-sheller, forage
harvester, snow blower, and several other implements so that
all could be self-propelled.
In North America in the 1950s
FergusonTM had a line of implements including a forage
harvester, baler, and combine that mounted on the
FergusonM tractor to make these implements self-propelled
machines. For the most part, farmers did not accept this
concept, in that most Minneapolis MolineTM units were used
by farmers as single-purpose
and FergusonTM sales were so low that the models were
discontinued. About 1955,Jean Nolle applied the tool-carrier
concept to animal-drawn implements with his development
of a wheeled tool carrier called the Polyculteur, and about 3
yr later the National Institute of Agricultural Engineering in
Great Britain began work on an animal-drawn toolbar. Many
agricultural machinery research organizations in the tropics
and semitropics followed with their own designs. Probably
the greatest effort was expended by ICRISAT, which began a
decade of research on bullock-drawn wheeled tool carriers in
Animal-drawn wheeled tool carriers have not been accepted by farmers, although about lG,OOuhave been made in
the world and sold at subsidized prices over the past 30 yr.6
The designs have not been accepted because they are too
costly for the benefits derived; the tool carrier must be made
heavy enough to support the tool with the greatest draft so that
the tool carrier is overdesigned for lighter implements. On the
economic side, the tool carriers must compete with native
ards, sowing of seed by hand, low grain prices, and humers
who have little capital. The animal-drawn tool carriers
performed well technically, but because they and their
implements were more sophisticated and costlier than the
implements or practices they were to replace, and because
they did not increase yield or reduce costs, they were not
13.3 Examples of
estimating the cost of
field machinery
I. A farmer purchased a new pull-type hay baler for making
small rectangular bales, powered by a 20-hp gasoline engine.
He paid 10% below the list price of $10,000. Since he makes
3 cuttings annually on his 50 ha of haycrop, the machine will
bale 150 ha/yr. He likes to use late model machines, so he
intends to trade the baler after 5 yr. While baling, he drives
at 8 km/h and picks up winclrows made from 3-m swaths.
Field efficiency is 70%. His records show that the tractor to
pull the baler costs $5.00/h. The driver is paid $7.00/h. No
labor other than the tractor driver is required. Gasoline costs
$0.25/liter. The interest rate is 10%.
What is the average hourly cost of operation. not including the cost of baler twine? What is the estimated value of the
machine at the end of 3 yr? The completed worksheet is
shown in Table 13.7.
13.7. Worksheet
example 1, metric-- units.
New machine
initial list price
Pull type hay bailer
- 20
Estimated life
-- 3
150 ha
8 km/h
Hectares to work per year
Field speed
Width of effective swath
Field efficiency
Effective capacity = (line 2) x (line 3) x (line 4) + IO
(6) Annual hours of operatiot = ;line 1”,+ (ine ;i”= Lij~~
(7) Expected age at riade-in
(8) Average annual fixed cost per $1000 initial list price (ilp)
Use Table 13.3 (10% interest) or-Table 13.4 (20% interest)
(9) Average annual fixed cost = (line 8) x (ilp/iOOO)
= 174 x ~/loo0
(10) Fixed cost par~hectare = line 9 + line 1 = $ 1,740 + -- 150
(11) Fixed cost per hour = line 9 + line 6 = $ 1,740 + 69
Repeirs Age and hours on machine purchased by you
(12) Total accum(Jlated repair hours at trade-in = line 6 x line 7
a -..-69 hiyr x 5yr
(13) RepAir cost factor
(14) Accumulated repair cost = ilp + 1000 x line 13
= $ ~oJmm + 1,000 x &
(15) Annual average repair cost = line 14 + line 7 = $ -se
+ --55
(16) Average repair cost per hectare = line 15 + line 1 = .__108 + J5l5(17) Average repair cost per hour = line 15 + line 6 = 108
+ ..J?-
1.68 ha/h
89 hlyr
--- $174 /$I 000 ilp
A,-$1 740 lyr
$11.60 /ha
-- $19.55 Ih
= -----!I
445 h
$54 /I 000 ilp
3s --.--- $540
$108 /yr
$1.21 fh
Fuel and lube
(16) Fuel and lube = tractor or engine hp x F & L factor x fuel cost
= .-Lhp
x .12_6_Z’_F
& L factor x $ ~3). !litcr
$1.3Q /h
$7.00 Ih
.-.__$5.00 Ih
$14.51- Ih
--. $8.64
$34.06 /h
$20.24 /ha
(19) Labor cost = number of operators x hourly rate = __.I,- x $-ALE. Ih
Tractor cost for towed implement
(20) Tractor hourly cost
Total operating costs:
(21) Operating cost per hour = repairs (17) + fuel (18) + labor (19) + tractor (20)
m -Lx
+ Lx_
+ .E
+ 5.0&L
(22) Operating cost per ha = line 21 t line 5 = 14.51 + ,[email protected] COST
(23) Total cost per hour = operating cost (line 21) + fixed cost (line 11)
= $ Jla./h
+ $ 12;9_/h
(24) T’otalcost per hectare = operating cost (line 22) + fixed cost (line 10)
= $ j.68.lha
+ $ ,J’l._/ha
Table 13.8. Worksheet
a-row pedestrian seeder
(Sri Lanka)
example 2, English units.
New machine
initial list price
Estimated life
Acres to work per year
Field speed
Width of effective swath
Field efficiency
Effective capacity = (line 2) x (line 3) x (line 4) + 8.25
+ 8.25
= 1.8 x 1.3 X.60
(8) Annual hours of operation = (line 1) + (line 5) = 20 + 0.15
20 ac
1.6 mph
1.3 ft
(7) Expected age at trade-in
(8) Average annuai fixed cost per $1000 initial list price (ilp)
Use Table 13.3 (10% interest) or Table 13.4 (20% interest)
(9) Average annual fixed cost = (line 8) x (ilpilOO0)
= - 171 x .~ 100 HOOO
(10) Fixed cost per acre E line 9 + line 1 = $ 17.10 + 20
(11) Fixed cost per hour = line 9 + line 6 = $ ______
17.10 + 133
Age and hours on machine purchased by you
0 15 aclh
133 h/yr
8 Yr
$171 /$I000 ilp
$17.10 lyr
$0.88 lac
$0.13 /h
= --
(12) Total accumulated repair hours at trade-in = link 8 x line 7
= I ‘2 -. ~_Wr x Il__yr
(13) Repair cost factor
(14) Accumulated repair cost = ilp + 1000 x line 13
= $ x-c
1,000 x -m
(15) Annual average repair cost = line 14 + line 7 = $ 51 +
(16) Average repair cost per acre = line 15 + line 1 = 6.38 + 20
(17) Average repair cost per hour = line 15 + line 6 = 6.38 + 133
0 yr
1084 h
$518 /IO00 ilp
$8.38 lyr
Fuel and lube
(18) Fuel and lube = tractor or engine hp i F 8 L factor x fuel cost
F&Lfactor x $ /US
= --v-hp
x I
$0.20 Ih
$0.25 Ih
81.67 iac
$0.38 ih
82.53 iac
(19) Labor cost = number of operators
Tractor cost for towed implement
(20) Tractor houriy cost
Total opsratlng costs:
(21) Operating cost per hour = repairs
= 05
(22) Operating cost per acre = line
x hourly rate = 1
x $-.$J
(17) + fuel (18) + labor (19) + tractor (20)
0 + .20 +
+ linu 5 = L 25 t I 15
(23) Total cost per hour = operating cost (line 21) + fixed cost (line 11)
(24) Total cost per acre = operating cost (line 22) + fixed cost (line 10)
= $ 1.67/ac
+ $ .86ac
2. A farmer in Sri Lanka has purchased a new 2-row
pedestrian seeder with a list price of $100 at a 1 o discount.
The interest rate is 20%. The seeder has an effective swath of
1.3 ft and will be used to plant 20 acres/yr for 8 yr. Speed is
1.6 mph, and field efficiency is 60%. The seeder needs one
operator, who is paid $0.2O/hr.
What is the f=ed cost, operating cost, and total cost per
acre? The completed worksheet is shown as Table 13.8.
3. What is the average hourly cost for a compact tractor
with a 12-hp gaholine engine over a period of 10 yr? List price
iS $3,500. The tractor will be used 600 h/yr on a variety of light
to heavy jobs. The tmctor can be purchased at 10% below list
price. The interest rate is 10%. Fuel costs $O.fiO/liter. (Note
that on the worksheet, items 1,2,3,4,5, 10, 16,22, and 24 do
not apply, since they refer to hectares and acres.)
Answer: For 12,000 h estimated life, repair group 2, and
depreciation group A, total cost = $2.49/h, of which $1.81 is
operating cost and $0.68 is fixed cost.
1. American Society of Agricultural Engineers (1985) ASAE standards.
Agricultural machinery management data. St. Joseph, Michigan. 156 p.
2. Campbell J K (1978) Selecting field machinery - estimating cost. Agric.
Eng. Ext. Bull. 431. Cornell University, Ithaca, New York.
3. Ibid., p. 4.
4. American Society of Agricultural Engineers (1977) ASAE yearbook.
Joseph, Michigan.
5. Bowers W, Hunt D R (1969) Application of mathematical formulas to
repair cost data. ASAE Paper 69-159. American Society of Agricultural
Engineers, St. Joseph, Michigan.
6. Starkey P (1988) Animal-drawn wheeled toolcarriers: perfected yet
rejected- a cautionary tale af development. 131 p. Deutsche Gesellschaft
FairTechnische Zusammenarbeit, Eschbom.
Cronk B J, Williams T H, Krismnan P, Kemble L J (1987) Optimal width
equations,for various tillage implements. ASAE Paper 87-1612. American
Society of Agricultural Engineers, St. Joseph, Michigan.
Rogin L (1931) The introduction of farm machinery in its relation to the’
productivity of labor in’ the agriculture of the United States during the
nineteenth century. University of California Press, Berkeley, California.
Uohnson Reprint Corp., New York 19661
Ulloa 0 T, Esmay M L (19g7) Machinery selection model for Mexico. ASAE
Paper 87-5521. American Society of Agricultural Engineers, St. Joseph,
and acr
ASAE = American Society of Agricultural Engineers
CAAMS = Chinese Academy of Agricultural Mechanization
CDA = contro!ied droplet application
CIAT = Centro International de Agricultura Tropical
CIP = International Potato Center
D = draft
DIN = Deutsche Industric Norm
= ChWhl
EC = effective capacity
fr = coefficient of rolling friction
FAO = Food and Agricultilre Organization
ICRISAT = International Crops Research institute for the SemArid Tropics
ilp = initial list price
IRRI = International Rice Research Institute
WC = inches of water column
LDC = less developed country
LER = land equivalent ratio
LPG = liquefied petroleum gas
LSU = Louisiana ,State Llniversity
MC = moisture content
PTO = power-take-off
RH = relative humidity
SAE = Society of Automotive Engineers
SI = Le SystPme International d’Unit&
SP = static pressure
TDN = total digestible nutrients
ULV = ultralow volume (sprayer)
wh = wet basis
A. Metric - English
pound (lb)
pound (lb)
metric ton (1)(2205 lb)
pound/square foot (Ib/sq ft)
pound/acre (Ib/ac)
ounce/US gallon (0tiUS gal)
pound/US gallon (lb/US gal)
Non-.% metric unit
= SI metric unit
= non-S1 metric unit
kilogram (kg)
kilogram (kg)
gram/square centimeter (g/cmP) 2.048
kilogram/hectare (kg/ha)
gram/liter (g/liter)
&am/liter (&liter)
lbisq ft
oz/US gal
lb/US gal
millimeter (mm)
millimeter (mm)
centimeter (cm)
centimeter (cm)
centimeter (cm)
kilometer (km)
square centimeter (cm*)
square meter (mz)
square meter (mz)
hectare (ha)
hectare (ha)
mil (0.001 inj
inch (in)
inch (in)
foot (ft)
square inch (sq in)
square foot (sq ft)
acre (ac)
acre (ac)
square mile (sq mila)
sq in
sq n
sq mile
cubic inch (cu in)
cubic inch (cu in)
cubic foot (cu ft)
fluid ounce (fluid oz)
pint (Pt)
US.quart (US qt, liquid)
US &art (US qt, dry)~ ‘~
US gallon (US gal)
Imperial gallon (Imp. gal)
bushel (bu)
acre-foot (ac-ft)
acre-inch (ac-in)
quart/acre (qt/ac)
US gallon/acre (US gal/at)
cubic foot/second (cu Ws)
cubic foot/second (cu Ws)
cubic foot/minute (cfm)
cubic meter (ml)
milliliter (ml)
milliliter (ml)
cubic meter (m3)
cubic meter (m*)
liter.hectare (liter/ha)
lifer hectare (liter/ha)
liter hectare (liter/ha)
cubic meter/second (ml/s)
liter/second (literis)
0.000471 cubic meter/second (m%)
cu in
cu in
fluid oz
US qt, liquid
US qt, dry
US gal
Imp. gal
US gallac
cu ft/s
cu fvs
on next page
A. continued
Non-S1 metric unit
foot/second (Ws)
ounce (02)
pound (lb)
ton (2205 lb)
kilogram force (kgf)
= St metric unit
= non-S1 metric unit
meter/second (m/s)
ton (2205 lb)
pound/square inch (psi)
pound/square foot (psf)
in of water
in of mercury
in of mercury
atmospher t
Pascal (Pa)
Pascal (Pa)
Pascal (Pa)
Pascal (Pa)
Rascal (Pa)
in of water
in of mercury
in of mercury
British thermal unit (BTU)
foot-pound (ft-lb)
horsepower-hour (hp-h)
kilowatt-hour (kWh)
calorie (c)
British thermal unit/hour-footdegree Fahrenheit (BTU/h-ft-OF)
Brttish thermal unit-inchlhoursquare foot-degree Fahtenheit
(BTU-in/h-sq ~-OF)
British thermal unit/hour-square foot
(BTU/h-sq ftj
langley/minute (langley/min)
British thermal unit/square foot
(BTU/sq ft)
British thermal unit/US gallon
(BTU!US gal)
British thermal unit/pound (BTU/lb)
kilojoule (kJ)
joule (J)
megajoule (MJ)
megajoule (MJ)
joule (J)
megajoule (MJ)
joule/square centimeter (J/cm*)
watt/meter-kelvin (W/m-,K)
watt/meter-kelvin (W/m-K)
BTU in/h-sq ft/“F
watt/square meter (W/m2)
watt/square meter (W/mz)
kilojoule/square meter (kJ/m2)
BTU/h-sq ft
kilojoule/square meter (kJ/m*)
BTUlsq ft
kilojoule/liter (kJ/liter)
kilojoule/kilogram (kJ/kg)
BTU/US gal
ton (refrig)
British thermal unit/minute (BTU/min)
horsepower (hp)
foot-pound/minute (ft-lb/minr
ton (refrig)
kilowatt (kW)
kilowan (kW)
watt (W)
kilowatt (kW)
Allbright L D (1978) Metrification. Agric. Eng. Ext Bull. 423. Cornell University, Ithaca, New York. 16 p. (adapted)
Appendix 0. Rates of work, draft, and Dower
Rates of work’
Manual tillage
Slash and burn
Tillage with hoe
Hoeing, flooded soil
Spade, 25 cm depth
Animal tillage
2 oxen with ridging plow
2 oxen with ard.
4 horses with 2-bottom 14” moldboard
6 horses with 2-bottom 14” moldboard
12 horses with 3-bottom 16” moldboard
6 horses with 8-ft tandem disk harrow
4 horses with 12-ft spike-tooth harrow
8 horses with 12-ft spring-tooth harrow
Water buffalo plowing flooded soil
Water buffalo comb harrowing
5 water buffalo trampling (puddling) wet soil
2 bullocks with plank leveller
Tractor tillage
4.5hp pedestrian tiller
4.5hp tractor and 4-bottom disk plow
80-hp tracklayer and 7-bottom disk plow
5hp power tiller plowing wet soil
10-hp double-axle pedestrian tractor tilling wet soil
10-hp hydrotiller
12.5-hp compact tractor plowing wheat stubble
40-hp tractor rotovating wet soii
5-hp single-axle pedestrian tractor with
puddling wheels and comb harrow
Clearing virgin forest with tracklayer
Clearing secondary forest with tracklayer
Clearing bush with tracklayer
Manual planting
Using dibble stick
Seeding in premarked rows and covering by foot
Push- or pull-type planter in dry soil
IRRI row seeder with pregerminated rice seed
sown in wet soil
Animal planting
Bullock-drawn seed drill
2 bullocks and ard, broadcasting and covering seed
4 horses and 8-ft disk drill
6 horses and 12-ft disk drill
2 horses and 2-row maize planter
2 horses and 1-row potato pianter
continued on next page
Appendix B. continued
Rates of work’
Tractor planting
Airplane broadcasting of rice
5hp pedestrian seeder (rice)
60-hp tractor and 4-row maize planter
Manual weed and pest control
Hand weeding transplanted rice
Hand weeding rice in broadcast field
Hand weeding pricein dibbled field
Hap3 ::!eeding rice in drilled field
30-l 50
Rotary push-type weeder in rice
Iland-carried IRRI power weeder
Knapsack sprayer
Animal weed and pest control
2 horses and 2-tow (maize) shovel cultivator
Tractor weed and pest control
35hp tractor with cultivator
Airplane applying herbicide
Knapsack power duster (in rice)
Tractor-mounted sprayer (in rice)
Manual harvesting, threshing, and processing
Harvesting rice with sickle or knife
Reaping with a scythe
Bunding rice into sheaves
Hauling sheaves to thresher
Threshing rice with hand sticks
Threshing rice with flail
Threshing rice on a bamboo ladder
40 kg/h
Winnowing grain by tossing in wind
200-l 200 kg/h
Hand-driven winnower
Harvesting, threshing, and processing with animals
2 horses and 6-ft reaper
4 horses and 8-ft binder
2 horses and 1-row maize binder
6 horses and 1-row maize picker
16 horses and 14-ft combine
2 horses and 6-ft mower mowing hay
2 oxen threshing by treading
Engine-powered harvesting, threshing, and processing
5-hp pedestrian windrower
Threshing rice by treading with 5 water buffalo
600-2000 kg/h
Threshing rice by treading with tractor
350-700 kg/h
5-hp RRI axial-flow thresher, 4 men feeding
0.18 t grain/h
Small (112-m)combine
continund on opposite page
Appendix B. continued
Equations for draft and power requirements2
(S = km/h or mph, d = depth in cm or in, M = mass in kg or lb,
F = throughput rate in kg/set or IWsec)
Moldboard plow draft per unit of cross-section of furrow slice:
: Draft (N/cm*) = 2 + 0.013 S2
Draft (lb/W) = 3 + 0.05 S2
: Draft (N/cm*) = 3 + 0.020 S.*
Draft (lb/in*) = 4.5 + 0.08 S2
Silty clay
: Draft (N/cmz) = 7 + 0.049 Sz
Draft (lb/in*) = 10.24 + 0.185 S’
Disk plow draft per unit of cross-section of furrow slice:
: Draft (N/cm3 = 2.4 + 0.045 Sz
Draft (lb/in*) = 3.4 + 9.17 S2
: Draft (N/cm*) = 5.2 + 0.039 S2
Draft (IbiirV) = 7.6 + 0.15 S*
Lister at 6.75 km/h and 36-cm bottom:
Silty clay loam
: Draft (N/cm*) = 21.5 dZ
Draft (lb/W) = 31.2 d*
Disc harrow
: Draft (N/cm2) = 11.7 M
Draft (lb/W) = 1.2 M
Field cultivator operating at 8.3-cm depth, draft per tool:
Clay loam
: Draft (N/cm?) = 480 + 48.1 S
Draft (lb/Z) = 108 + 16 S
Subsoiler draft per shank:
Medium or clay loam : Draft (N/shank) = 175 d-280 d
Draft (lb/shank) = 100 d-l 60 d
draft per unit width
: Draft (N/m) = 4400-l 1600
Draft (lb/ft) = 300-800
Spike-tooth harrow
: Draft (N/m) = 440-730
Draft (lb/A) = 30-50
Spring-tooth harrow
: Draft (N/m) = 1460-2190
Draft (Ib/ft) = 100-l 50
Rod weeder
: Draft (N/m) = 880-1830
Draft (Ib/ft) = 60-125
Roller or packer
: Draft (N/m) = 440-880
Draft (Iblft) = 30-60
Row planter in loam soil and good seedbed:
Seeding only
: Draft (N/row) = 450-800
Draft (lb/row) = 100, r 80
Seed, fertilizer,
: Draft (N/row) = 1100-2000
Draft (lb/row) = 250-450
continued on next page
Appendix B. continued
Grain drill
: Draft (N/furrow opener) = 130-450
Draft (lb/furrow opener) = 30-l 00
: Draft (N/m width) = 115d-230d
Row cultivator
Draft (Ib/ft width) = 20d-40d
: Draft (N/m width) = 446 + 21.7 S
Rotary hoe
Draft (Ib/ft width) = 30 + 2.4 S
Anhydrous ammonia applicator
~Draft= 1800 N/knife
Draft = 400 lb/knife
Potato digger
Draft of 2.2-3.5 kN/row + rotary power of 0.75-l .5 kW/row
Draft of 500-800 lb/row + rotary power of l-2 hp/row
Sugar beet harvester
Draft of 2 to 4 kN/row + rotary power of 1.5-3.0 kW/row
Draft of 450-900 lb/row + rotary power of 2-4 hp/row
Rotary power at implement engine or tractor Pi0 for field machines
(does not include power required to overcome rolling resistance):
: 1.2 kW/m of cut
Cutter bar mower
0.5 hp/ft of cut
Cutter bar mower
: 3.5-4.90 kW/m of cut
1.5-2 hp/ft of cut
Flail mower-conditioner : (8.2 + 2.13 F) kW
(11.0 + 1.3 F) hp
Side delivery rake
: (-0.186 + 0.052 S) kW
(2.4 m or 8 ft wide)
(-0.25 + 0.25 S) hp
Baler, rectangular
: (2.95 F) kW
(1.8 F) hp
Baler, rectangular, tough
crop, high density
: (4.4 F) kW
(2.7 F) hp
Forage harvester, precision-cut
: (1.5 + 3.3 F) kW
(2 + 2 F) hp
Green alfalfa
: (2.0 + 4.4 F) kW
(2.7 + 2.7 F) hp
: (3.0 + 6.6 F) kW
Haylage or hay
(4 + 4 F) hp
Self-propelled combine (20% MC straw, chaff, and husks)
Small grain and beans : (7.5 + 7.5 F) kW
(10 + 4.6 F) hp
: (22.5 + 22.5 F) kW
(30 + 13.8 F) hp
Cotton picker
: 7.5-l 1.OkW/row
1O-l 5 hplrow
1. Food and AgricultureOrganization (1976) Mechanization of rice production. India-Nigeria-Senegal. international Coordinated Research Project
1970-76. Rome. p. 146-t49; and Washburn R S, Merrick D (1936) Tillage,
planting and harvesting equipment on grain farms and rates of doing field
work with these implements when drawn with horse and with tractor power.
Bureau of Agricultural Economics, USDA, Washington, D.C. p. 45-51
2. American Society of Agricultural Engineers (1983) Agricultural engineers yearbook. St. Joseph, Michigan.
Appendix 6. Bullock training’
Nose ringing
Bullocks must have nose rings fixed for control and guidance. The rings
must be made of durable metal. No ropes or corrosive rings should be
To insert the ring, the animal’s head should be put down with the horns
resting on the ground and the nose in the air. The nose should be pulled
out slightly and the ring pierced through the sofl part. The ring must be
examined afterwards and sharp pieces of metal removed.
To prevent bullocks from injuring each other, the tips of the horns must be
removed. Care has to be taken that not too much is removed to avoid
bleeding. Some horn is advantageous because it prevents the animal from
pulling its head out of the yoke.
If bleeding occurs, use a clean cloth or cotton wool to stop it. Cover the
bandage with Gentian Violet or Stock balm to prevent infection, and wash
off the blood.
Training is divided into several sections. The time spent in each section
of the training varies considerably depending on the temperament of the
animal and its ability to learn. Training should be done during the cooler
parts of the day.
In the morning
7-11 am
In the evening
4-6 pm
As few people as possible should be present during training to prevent
the bullock from becoming nervous. Bullocks aiso become nervous when
the training is done too quickly, or when the trainer shouts or beats them.
The general rule is: Never Beat Bullocks.
Preparation for training (7 d)
At tirst, the animal must be calmed. Through frequent petting and talking
during feeding and watering, Ytgrows accustomed to its trainer. The
bullocks movements should be restricted by either tying it to a post or
stabling it. Names can be given to bullocks, as this will be helpful later
during verbal training.
Yoking (3 d)
Two types of shoulder yokes, 5-and 7-R wide, are used with bullocks. The
shorter yoke is easier to use in the yoking. The trainer may need
assistance in the yoking because of the temper of the animals. The
stronger animal should always be on the right side. especially when
plowing, for the right-hand bullock must walk on plowed ground.
The rope between the nose rings should be shortened for untrained
bullocks so that their heads are slightly turned toward one another. Once
the animals are trained, a longer rope can be used.
On the second day, the bullocks should be yoked and taught to move
as a team.
Cn the third day, the teaching of verbal signals for starting and stopping
should begin. The verbal signals must sound different so that the bullocks
will not be confused.
Starting bullocks
Stopping bullocks
A trail should be used to teach them to walk in a straight line.
Fulling a sled (3-6 d)
The bullocks must get used to pulling weight. A flat wooden sled (size ll/2 x 3 ft), which can be used later for transporting the implements to the
field, is advisable.
The teaching of verbal and physical signals for starting, stopping,
turning, and backing should continue from the first day. The next day apply
some extra weight to the platform or use a log to get the bullocks used to
pulling heavy weight for a period of time. Teaching of signals should
On the third day, begin practicing walking in straight lines on afield with
continued teaching of signals.
Another 2-3 d may be needed for field practice. A furrow should be
made across the field to teach the bullocks to follow it. To learn to walk in
the furrow, the animals must be alternated.
Field equipment (7 d)
About 1 wk should be al!ocated for field training with equipment such as
plows, ridgers, or carts. Considerable practice is needed to teach the
animals to pull in a straight line and to enable the trainer to learn how to
control them and the plow or ridger at the same time. Patterns should be
avoided in the training, because the bullocks may begin to move by habit
and not by command.
1. German Agency for Technical Cooperation (1977) Agricultural extensron handbook. Ghanaian-German Agricultural Development Project,
Northern and Upper Regions. Eschborn, Federal Republic of Germany.
Appendix D. Nebraska Tractor Test
- rc,
..~ ~~.~..
. tratio,;, but it
me retawe we or 1
is not a true measure or now
much power will be available in
the field.
Average fuel efficiency in horsspower-hours per gallon. Ths
more efficient the tractor is. the
larger this value will be and the
greater the fuel economy.
inch wg
Two Hours
m5 7,
__~~~~~~ .,..,,
Rated En&be Speed - Two hours (FTO Speed-998 rpm)
Maximum PTO horsepower is a
convenient means to compare
,[email protected],
Power “rawhlr
-limp. “F ,x:i
Fuel Conrun~ptioe Hp.hrigal Coo,.
iUhJ ,&+Wh,
Available Power - Two Hours 6th (3-2) Gear
6.38 2101 3.90 ii.613 0.459 15.21
121.012, 10.279, 12.996) kK8) (10.X)
inch “g
100.56 5915
(74.9% ,263,)
75% of Pull a1 Maximum Power - Ten Hours 8tb (3.2) Gear
6.69 2184 2.84 5.723 0.501 13.yP
fS9.4/1 CIY.851 00.77,
121.663) wm,
12.713, ,*7.2, (0.4) (J.7,
50% of Pull at Maximum Power-Two
Hours 8th (3-2) Gear
1RY ~56 ~57
4.535 0.5X4 I,.95
6.83 2206 l.YY ‘~
54.18 2975
140.401 (13.23, ,!“.99,
,1;./.57, ,u.3*5, ,2.3rj, (57.2, ,G, ,,L,
vx 71
Fuel efficiency at 50% of pull.
Note that tuel efficiency is higher
at reduced speed than at
maximum throttle, which shows
that throttling back and shifting
to a higher gear saves fuel.
50% of Pull at Reduced Engine Speed - Two Hours 16th (4-l) Gear
186 59
6.84 1449 I.YI 3.740 0.481~
continued on opposite page
Appendix D. continued
78.21 12915
fS8.36) f57.151
2.27 2161
2nd (1-P) Gear
94.28 12476
(70.30, 01.19,
2.83 2099
3rd (l-3) Gear
186.4) (7.2,
95.94 12348
I71.54, ,503,
2.91 2100
4th (2.11 Gear
5th (2-Z) Gear
17.8, f9.<,
6th (3-I) Gear
p.3, (10.6,
7th (2.3) Gear
(8.9, (11.1,
8th (3.2) Gear
,86.,1 111.1, (16.71
9th (Y-3) Gear
4.69 ,2101
5.25 2100
6.37 2100
175.62) 126.54) f10.25,
WJ, ,,I. 7,
IN 8th (3-P) GEAR
Crankshaft S!xed ram
8.04 2100
(73.57) eo.+8,
Percent increase in pull at reduced ccankshatt speeds. A
tractor whose pulling power rises
substantially during the first 20%
reduction in speed has good iugging ability. This tractor’s pull increases 9% when speed drops
Slip 96
Available Power-Tk.0
75% of Pull at Maximum
50% of Pull at Maximum
50% of Pull at Reduced Engine Speed-Two
Bystander in 12th (4.3) gear
With Balbsr
Without Ballast
Rar Tim
--No., Size.ply & psi (kpn) Inner Two 18.4-38;8; 16 ,llO, tnncr Two 18.4.58;8: 16 crrv,
-Liquid (each)
--Can I,“” krch,
--No.. size.ply & psi ,kPd
--Liquid ,each!
-cart bon (each,
Hcigbcor Dnrbu
St& [email protected] with Opnmr--Reas
outer ‘TWO18.4.Y8:6: LS,110,
IS, lb (73 kg1
Two IL”“.IliSL: 6: 52 wo,
5s lb f26 kl
19.5 in ,195 mm,
llS3” Ill ,r,wb,
S61” Ii7 (1637 kg,
,494” tll (6776 kg)
ouwr Two 18.4.YB:6; 16(110,
TWO11.““-ISSL 6; 32 (220,
Non19.5in ,195 mm,
10685lb ,A?47 kg,
3195 lb ,I585 b#,
I4180 lb 16132kg,
Koelsch R K (1978) Choosing a tractor using the Nebraska Tractor Tests.
Northeast Regional Agricultural Engineering Service, Cornell University,
Ithaca, New York. NRAES FS-16.
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