Save and Grow: Cassava

Save and Grow: Cassava
copertina cassava save and grow.pdf
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25aprile2013
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SAVE AND GROW
SAVE AND GROW: CASSAVA
This guide is the first on the
practical application of FAO’s
“Save and Grow” model of
agriculture to specific
smallholder crops and farming
systems. It comes as cassava
production intensifies
worldwide, and growers shift
from traditional cultivation
practices to monocropping,
higher-yielding genotypes, and
greater use of agrochemicals.
Intensification carries great risks, including soil nutrient
depletion and upsurges in pests and diseases. The guide shows
how ecosystem-based “Save and Grow” approaches and practices
can help tropical developing countries to avoid the risks of
unsustainable intensification, while realizing cassava’s potential
for producing higher yields, alleviating hunger and rural poverty,
and contributing to national economic development.
CM
MY
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CMY
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A GUIDE TO SUSTAINABLE PRODUCTION INTENSIFICATION
FAO
Save and Grow:
Cassava
A guide to sustainable production intensification
FOOD AND AGRICULTURE ORGANIZATION
OF THE UNITED NATIONS
Rome, 2013
The designations employed and the presentation of material in this information
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preference to others of a similar nature that are not mentioned.
ISBN 978-92-5-107641-5 (print)
E-ISBN 978-92-5-107642-2 (PDF)
© FAO 2013
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Foreword
C
assava is a tropical root crop, originally from Amazonia, that
provides the staple food of an estimated 800 million people worldwide. Grown almost exclusively by low-income, smallholder farmers,
it is one of the few staple crops that can be produced efficiently on a
small scale, without the need for mechanization or purchased inputs,
and in marginal areas with poor soils and unpredictable rainfall.
Since 2000, the world’s annual cassava production has increased by
an estimated 100 million tonnes, driven in Asia by demand for dried
cassava and starch for use in livestock feed and industrial applications,
and in Africa by expanding urban markets for cassava food products.
There is great potential for further production increases – under
optimal conditions, cassava yields can reach 80 tonnes per hectare,
compared to the current world average yield of just 12.8 tonnes.
Booming demand offers millions of cassava growers in tropical
countries the opportunity to intensify production, earn higher
incomes and boost the food supply where it is most needed. But how
smallholder cassava growers choose to improve productivity should
be of major concern to policymakers. The Green Revolution in cereal
production, based on genetically uniform varieties and intensive use
of irrigation and agrochemicals, has taken a heavy toll on agriculture’s
natural resource base, jeopardizing future productivity. In moving
from traditional, low-input to more intensive cultivation, small-scale
cassava growers should not make the same mistakes.
Sustainable intensification of cassava production is the subject of
this guide, the first in a series to the practical application of FAO’s
“Save and Grow” model of agriculture to specific smallholder crops
and farming systems. Endorsed by FAO in 2010, “Save and Grow” is an
ecosystem approach to agriculture that aims at improving productivity
while conserving natural resources. It promotes practices that can
help the world’s half a billion smallholder farm families to produce
more from the same area of land while enhancing natural capital and
ecosystem services.
Drawing on two decades of research findings and on-farm experiences in Africa, Asia, Latin America and the Caribbean, the guide
presents an eco-friendly approach to managing cassava more intensively. Many recommended practices combine traditional knowledge
with modern technologies that are adapted to the needs of small-scale
iv Save and Grow: Cassava
producers. They include: minimizing tillage to protect soil health,
optimizing timing and methods of planting, and using biological
control agents to counter pests and diseases. The guide shows how
well-balanced applications of mineral fertilizer, in combination with
intercropping, crop rotation, mulching, manure and compost, can
make a cassava-based farming system not only more productive and
profitable, but also more sustainable.
The adoption of “Save and Grow” agriculture will require significant
improvements in the provision of extension, inputs and production
credit to small-scale producers. Moreover, FAO recognizes that
improved productivity may not bring about sustainable, long-term
development outcomes: a major effort is needed to integrate smallholders into higher levels of value addition. Transforming cassava into a
multipurpose subsector that generates income, diversifies economies
and ensures food for all will require political commitment, investment,
institutional support and a demand-driven approach to technology
development.
This guide will be a valuable resource for policymakers in assessing
how a dynamic cassava sector can help them to achieve their goals of
poverty alleviation, economic development and food security, and of
practical use to agricultural researchers, technicians and other professionals in preparing programmes for sustainable cassava production
intensification.
Clayton Campanhola
Director, FAO Plant Production and Protection Division
Contents
Foreword
Acknowledgements
Overview
iii
vi
vii
Chapter 1: Cassava, a 21st century crop
Chapter 2: Farming systems
Chapter 3: Varieties and planting material
Chapter 4: Water management
Chapter 5: Crop nutrition
Chapter 6: Pests and diseases
Chapter 7: Harvest, post-harvest and value addition
Chapter 8: The way forward
1
19
35
49
59
73
87
97
Annex tables
References
Abbreviations
109
121
129
vi Save and Grow: Cassava
Authors
This guide was prepared by
Reinhardt Howeler
CIAT emeritus scientist
NeBambi Lutaladio
and Graeme Thomas
of the FAO Plant Production
and Protection Division
Acknowledgements
The contributions of the following are
gratefully acknowledged:
Kolawole Adebayo (Abeokuta University
of Agriculture, Nigeria)
Jean Pierre Anota (FAO consultant)
Tin Maung Aye (CIAT)
Jan Breithaupt (FAO)
Hernán Ceballos (CIAT)
Swarup K. Chakrabarti (CTCRI, India)
Mark Davis (FAO)
Dominique Dufour (CIAT)
Emerson Fey (State University of West
Paraná, Brazil)
Marjon Fredrix (FAO)
Theodor Friedrich (FAO)
Gualbert Gbehounou (FAO)
Book design
Thomas+Sansonetti
Winfred Hammond (FAO)
Lawan Jeerapong (Department
of Agricultural Extension, Thailand)
Jippe Hoogeveen (FAO)
Josef Kienzle (FAO)
Lava Kumar (IITA)
Chikelu Mba (FAO)
Danilo Mejía (FAO)
Linn Borgen Nilsen (FAO)
Christian Nolte (FAO)
Bernardo Ospina Patiño (CLAYUCA)
Dai Peters (Great Lakes Cassava
Initiative)
Adam Prakash (FAO)
Chareinsak Rojanaridpiched (Kasetsart
University, Thailand)
Teresa Sánchez (CIAT)
Brian Sims (FAO consultant)
Mario Takahashi (Agricultural Institute
of Paraná, Brazil)
Namthip Thongnak (Thai Tapioca
Development Institute)
Bernard Vanlauwe (IITA)
Andrew Westby (University
of Greenwich, UK)
James Whyte (FAO consultant)
Amporn Winotai (Department
of Agriculture, Thailand)
Cover and illustrations
Cecilia Sanchez
Editorial assistance
Diana Gutiérrez
Overview
1. Cassava, a 21st century crop
The “food of the poor” has become a multipurpose crop that
responds to the priorities of developing countries, to trends in
the global economy and to the challenge of climate change.
ong regarded as unsuitable for intensification, cassava has
grown dramatically in importance in world agriculture. The
2012 harvest reached record levels, thanks to expansion of global
trade in cassava products and strong growth of output in Africa.
Production is intensifying worldwide. In the years ahead, cassava
will see a shift to monocropping, higher-yielding genotypes, and
greater use of irrigation and agrochemicals. But intensification
carries great risks, including upsurges in pests and diseases, and
depletion of soil nutrients. This guide shows how FAO’s “Save and
Grow” farming approach can help developing countries to avoid
the risks of unsustainable intensification, while realizing cassava’s
potential for producing higher yields, alleviating rural poverty and
contributing to national economic development.
L
2. Farming systems
Many smallholder cassava growers already practise three
key “Save and Grow” recommendations: reduced or zero
tillage, soil surface cover and crop diversification.
lanting cassava without prior tillage in degraded soils may
produce lower yields in the initial years; once soil health is
restored, however, untilled land can produce high yields at a
lower cost to the farmer and the farm’s natural resources. Mulch
and cover crops help to reduce weed infestations and create
soil conditions that improve productivity. Growing cassava in
associations, sequences and rotations increases net income per
unit area of land, and reduces the risk of crop failure. Intercropping
with grain legumes can produce higher incomes than
monocropping, and supplies food for the household. Protective
hedgerows reduce soil erosion, while rotating cassava with legumes
and cereals helps to restore soil health and yields.
P
viii Save and Grow: Cassava
3. Varieties and planting material
The full potential of cassava will not be realized until
production constraints are mitigated in higher-yielding
varieties, and cassava growers have access to disease-free
planting material.
he time is right for the genome-wide characterization of
cassava genetic diversity, to fill gaps in landrace collections,
and to create natural reserves to safeguard wild relatives. The
harmonization of passport and evaluation data on genebank
accessions should be a priority. Breeding should focus on
developing varieties that are well-adapted to specific agroecologies, cropping systems and end-uses, and produce good yields
with minimal need for agrochemicals and irrigation. The routine
multiplication and distribution of disease-free planting material
of improved varieties are essential for sustainable intensification.
While few countries have formal seed systems for cassava, a 3-tier
community-based system pioneered in Africa, involving NGOs
and farmer associations, has helped ensure that improved varieties
and healthy planting material are adopted by cassava growers.
T
4. Water management
Once established, cassava can grow in areas that receive
just 400 mm of average annual rainfall. But much higher
yields can be obtained with higher levels of water supply.
ptimizing rainfed cassava production requires careful
attention to planting dates, planting methods and planting
positions, and soil management practices that help to conserve
water. Although it can grow in areas with 400 mm of rainfall
a year, maximum root yields in Thailand were correlated with
rainfall totalling about 1 700 mm. Cassava responds well to
irrigation – full surface irrigation has doubled the root yield
obtained without irrigation; drip irrigation can produce about
the same yield as surface irrigation using 50 percent less water. In
Nigeria, root yields increased sixfold when the quantity of water
supplied by supplementary drip irrigation was equal to that of the
season’s rainfall. Supplemental irrigation that increased the total
water supply by 20 percent almost doubled root yields.
O
Overview ix
5. Crop nutrition
Combining ecosystem processes and judicious use of mineral
fertilizer forms the basis of a sustainable crop nutrition
system that produces more while using fewer external inputs.
lthough cassava produces reasonable yields on poor soils,
many varieties perform better with fertilization. Yields in
Africa, especially, could be markedly improved if farmers had
access to mineral fertilizer at a reasonable price. Farmers can
improve soil fertility with other “Save and Grow” measures.
Intercropping grain legumes, and mulching the residues of
legumes and native weeds, boosts root yields. When combined
with fertilizer, both alley cropping with deep-rooting leguminous
trees and the use of organic compost or farmyard manure produce
higher crop yields and net incomes. Options to reduce the loss of
soil nutrients to erosion include zero tillage, which maintains soil
aggregate stability and internal drainage, contour hedgerows of
vetiver grass, and the application of mineral fertilizer, which leads
to faster soil coverage by the plant canopy.
A
6. Pests and diseases
Protecting cassava with pesticide is usually ineffective and
hardly ever economic. A range of non-chemical measures can
help farmers reduce losses while protecting the agro-ecosystem.
rowers should use planting material of varieties with
tolerance or resistance to major pests and diseases, as well
as ecosystem-based practices, such as mulching, maintaining soil
organic matter, and planting intercrops to provide a habitat for
pest predators. Biopesticides, sticky traps and soapy water can help
control many insect pests. Plant health strategies should encourage
natural biological agents – the mass release of a tiny wasp defeated
serious outbreaks of cassava mealybug in Africa and Asia. To
prevent weeds overwhelming young plants, farmers should use
optimum planting densities and fertilization, and varieties with
vigorous early growth. Regular hand weeding can be as effective as
weed control with herbicides. Farmers need to exercise care in the
choice of the herbicides and should follow the advice of local plant
protection specialists.
G
x Save and Grow: Cassava
7. Harvest, post-harvest and value addition
Food for the household, feed for livestock, and raw material
for a wide array of value-added products, from coarse flour to
high-tech starch gels – cassava is a truly multipurpose crop.
arvested cassava roots are consumed directly by many farm
households or fed to their livestock. Roots can be processed
into granulated flour, or into high quality cassava flour which can
be used as a substitute for some of the wheat flour in bread and
confectionary. In Thailand and China, root starch goes into food
products, plywood, paper and textiles, and is used as feedstock for
production of sweeteners, fructose, alcohol and fuel ethanol. Two
recent cassava mutations have starch properties that are highly
valued by industry. The root is not the only useful part of the plant
– young cassava leaves make a nutritious vegetable, and plant tops
can be fed to cattle, buffaloes, pigs, chickens and silkworms.
H
8. The way forward
Governments need to encourage smallholders’ participation
in a sustainable cassava development agenda, and support
research and extension approaches that “let farmers decide”.
armer participatory research and farmer field schools have
proven very effective in promoting sustainable natural
resources management in smallholder production systems.
Cassava growers may also require incentives, such as payments
for environmental services, to adopt improved farming practices.
Action is needed to make mineral fertilizer and other inputs more
affordable to smallholders, and to provide them with quality,
disease-free planting material. Investment in roads, storage and
processing capacity in production zones will help cassava growers
retain a bigger share of value-addition. Policies should promote
private investment in cassava processing, and foster associations
that link producers with processors, promote standards and
share market information. While government subsidies may
reduce farmers’ exposure to price volatility, more sustainable
options are available, such as crop insurance and supply contracts
between food manufacturers and farmers’ cooperatives.
F
Chapter 1
Cassava,
a 21st century crop
The “food of the poor” has become
a multipurpose crop that responds
to the priorities of developing countries,
to trends in the global economy,
and to the challenge of climate change.
Chapter 1: Cassava, a 21st century crop 3
C
assava (Manihot esculenta Crantz) is one of some 100 species
of trees, shrubs and herbs of the genus Manihot, which is
distributed from northern Argentina to the southern United
States of America. While some studies indicate that cassava
has multiple centres of origin, others suggest that the cultivated
species originated on the southern edge of the Brazilian Amazon1-4.
Botanically, cassava is a woody perennial shrub, which grows from
1 m to 5 m in height. It is believed to have been cultivated, mainly for
its starchy roots, for 9 000 years, making it one of agriculture’s oldest
crops. In pre-Colombian times, it was grown in many parts of South
America, Mesoamerica and the Caribbean islands.
Following the Spanish and Portuguese conquests, cassava was taken
from Brazil to the Atlantic coast of Africa. By the 1800s it was being
grown along Africa’s east coast and in Southern Asia. Farming of
cassava expanded considerably in the 20th century, when it emerged
as an important food crop across sub-Saharan Africa and in India,
Indonesia and the Philippines.
Since it is sensitive to frost and
has a growing season of nearly
one year, cassava is cultivated
almost exclusively in tropical and
subtropical regions. It is grown
today by millions of small-scale
farmers in more than 100 countries, from American Samoa to
Zambia, under a variety of local
names: mandioca in Brazil, yuca
in Honduras, ketela pohon in
Indonesia, mihogo in Kenya, akpu
in Nigeria and sắn in Viet Nam.
Manihot esculenta has characteristics that make it highly attractive
to smallholder farmers in isolated areas where soils are poor and rainfall is low or unpredictable. Since it is propagated from stem cuttings,
planting material is low-cost and readily available. The plant is highly
tolerant to acid soils, and has formed a symbiotic association with soil
fungi that help its roots absorb phosphorus and micronutrients. To
discourage herbivores, its leaves produce two glycosides which, when
digested, produce highly toxic hydrogen cyanide. Since most of the soil
nutrients absorbed during growth remain in the above-ground part
Studies suggest that
cassava was first
cultivated, as many as
9 000 years ago, on the
southern edge of the
Brazilian Amazon, where
it is still grown today
4 Save and Grow: Cassava
of the plant, recycling the plant tops helps to maintain soil fertility.
Under drought stress, leaf production is reduced until the next rains.
Thanks to its efficient use of water and soil nutrients, and tolerance
to sporadic pest attacks, cassava growers, using few if any inputs, can
expect reasonable harvests where other crops would fail.
Cassava roots are more than 60 percent water. However, their dry
matter is very rich in carbohydrates, amounting to about 250 to 300 kg
for every tonne of fresh roots. When the root is used as food, the best
time to harvest is at about 8 to 10 months after planting; a longer
growing period generally produces a higher starch yield. However,
harvesting of some varieties can be “as needed”, at any time between
six months and two years. Those attributes have made cassava one
of the world’s most reliable food security crops.
Thanks to its roots’ high starch content, cassava is a rich source
of dietary energy. Its energy yield per hectare is often very high, and
potentially much higher than that of cereals5. In many countries of
sub-Saharan Africa, it is the cheapest source of calories available. In
addition, the roots contain significant amounts of vitamin C, thiamine,
riboflavin and niacin6.
Depending on the variety, they may also contain high levels of
cyanogenic glycosides, especially in the outer layers7. Once harvested,
therefore, cassava roots are peeled, then thoroughly cooked, or peeled,
grated and soaked to induce fermentation in order to release the
volatile cyanide gas. The mash is processed further – by drying,
roasting or boiling – into coarse flour and other food products. In
some countries, cassava is also grown for its leaves, which
contain up to 25 percent protein, on a dry weight basis5, 8.
Sun-drying or cooking reduces the hydrogen cyanide
to safe levels. Both leaves and roots can be fed to
Chapter 1: Cassava, a 21st century crop 5
farm animals, while stems can be used as firewood and a substrate
for growing mushrooms.
Cassava’s versatility does not end there. Its root starch can also
be used in a wide array of industries, including food manufacturing,
pharmaceuticals, textiles, plywood, paper and adhesives, and as
feedstock for the production of ethanol biofuel.
Cassava grows from
stakes cut from the
plant’s stems. After
3 months, some of its
fibrous roots begin
to swell with starch
relocated from the leaves.
Most of the root starch
forms after the sixth
month, when the plant
also achieves maximum
canopy size
6 Save and Grow: Cassava
Among the family of staple food crops, cassava was long regarded as
the least suited to intensification. Cassava stem cuttings are bulky and
can easily transmit serious pests and diseases, and the plant’s very low
rate of vegetative multiplication retards the adoption of new, improved
varieties. Unearthing cassava roots is labour-intensive, and the roots
themselves are cumbersome to transport and highly perishable: they
need to be processed within a few days of harvesting.
The Green Revolution approach to intensification, based on dwarf
varieties and high inputs of agrochemicals and irrigation, dramatically
boosted yields of wheat and rice, but it has proven inappropriate for
cassava in rainfed areas. Partly because it is grown in developing
countries, far less research and development has been devoted to
cassava than to rice, maize and wheat9.
But cassava’s importance in agriculture has changed dramatically.
Between 1980 and 2011, the global harvested area of cassava expanded
by 44 percent, from 13.6 million to 19.6 million hectares, which was the
biggest percentage increase among the world’s five major food crops.
In that same period, world cassava production more than doubled,
from 124 million to 252 million tonnes10.
Over the past decade, growth in cassava production has accelerated
(Figure 1). FAO estimates put the global harvest in 2012 at more than
280 million tonnes, representing a 60 percent increase since 2000 and
an annual growth rate double that of the previous two decades11. Since
2000, the growth rate of cassava output in Africa has been equal to
Figure 1 Growth in world production of major crops, 1980-2011 (index 1980=100)
240
220
Maize
200
Cassava
180
Rice
160
Wheat
Potatoes
140
120
100
Source: FAO. 2013. FAOSTAT statistical database (http://faostat.fao.org/).
2010
2011
2005
2000
1995
1990
1985
1980
80
Chapter 1: Cassava, a 21st century crop 7
Global cassava harvested area (ha/km2)
Tropic of Cancer
Equator
Tropic of Capricorn
0
>0-0.019
>0.019-0.194
>0.194-1.935
that of maize, while in South, Southeast and Eastern Asia the rate has
been almost three times that of rice10.
Another significant trend since the turn of the century is the
higher productivity of cassava-based farming systems. Growth in
production between 1980 and 2000 was due mainly to increases in
the harvested area, of some 3.7 million ha; yields grew at an annual
rate of just 0.6 percent. Since then, global average yields per hectare
have increased by almost 1.8 percent a year, from 10.4 tonnes per ha
in 2000 to 12.8 tonnes in 2011. While growth of cassava yields trailed
well behind that of other major food crops in the period 1980-2000,
the rate of increase over the past decade has exceeded that of potatoes,
maize, rice and wheat10.
Current average yields are still far lower than cassava’s potential. A
study by the International Center for Tropical Agriculture (CIAT) in
the 1990s estimated conservatively that – with improved crop and soil
management, and the use of higher yielding varieties more resistant
to drought, pests and diseases – cassava could produce an average
of 23.2 tonnes of roots per ha. On the current harvested area, that
amounts to more than 450 million tonnes a year.
A review of developments in the world’s cassava producing regions
reveals that diverse factors are driving increases in output and that
growers are responding to rising demand by intensifying production.
>1.935
Source: Adapted from Monfreda, C.,
Ramankutty, N. & Foley, J.A. 2008.
Farming the planet: 2. Geographic
distribution of crop areas, yields,
physiological types, and net primary
production in the year 2000. Glob.
Biogeochem. Cycles, 22: 1-19.
8 Save and Grow: Cassava
Figure 2 Growth in cassava production, harvested area and yield in sub-Saharan Africa,
1980-2011 Index: 1980=100
300
Production
280
260
240
220
200
180
Area
160
Yield
140
120
2010
2007
2004
2001
1998
1995
1992
1989
1986
1983
80
1980
100
Source: Annex Tables 1.1, 1.2 and 1.3
Figure 3 Growth in cassava production, harvested area and yield in Asia, 1980-2011
Index: 1980=100
200
180
Production
Yield
160
140
120
100
2010
2007
2004
2001
1998
1995
1992
1989
1986
1983
Area
1980
80
Source: Annex Tables 1.1, 1.2 and 1.3
Figure 4 Growth in cassava production, harvested area and yield in Latin America
and the Caribbean, 1980-2011 Index: 1980=100
200
180
160
140
Production
120
Yield
100
Source: Annex Tables 1.1, 1.2 and 1.3
2010
2007
2004
2001
1998
1995
1992
1989
1986
1983
Area
1980
80
Chapter 1: Cassava, a 21st century crop 9
Sub-Saharan Africa
Output of cassava has increased most markedly in sub-Saharan Africa,
which harvested 140.9 million tonnes – more than half of the global
harvest – in 2011. Between 1980 and 2000, production almost doubled,
from 48.3 million to 95.3 million tonnes, thanks to a 56 percent increase in the harvested area and 25 percent growth in yields. Between
2000 to 2011, expansion of the harvested area slowed to 18 percent,
but improvements in yields, from 8.6 tonnes to 10.8 tonnes per ha,
boosted production by almost 50 percent (Figure 2).
Cassava in sub-Saharan Africa is grown mainly on small holdings
by low-income farmers who make little or no use of external inputs.
It is usually grown with other crops, such as maize, rice, legumes,
melons, bananas and oil palm. It is still essentially a food crop – around
90 percent of harvested roots are destined for human consumption,
while around 10 percent is semi-processed as on-farm animal feed12.
Since 2000, cassava production has grown faster than the region’s
population, boosting the cassava food supply to almost 60 kg per
capita per year. Africans’ consumption of cassava is higher than that
of any other staple food, including maize. Almost all of it is consumed
as fresh roots or after processing into fermented flour products13.
By some estimates, urban Nigerians consume cassava at the rate of
0.2 kg per day14.
The biggest gains in cassava production since 2000 have been
in West Africa, where output rose by 60 percent, from 47 million
to 76 million tonnes. Productivity has increased as countries in the
subregion recognized cassava’s potential as an industrial crop that
could help to diversify farmers’ incomes, earn foreign exchange and
generate jobs12. Growth in output was particularly strong in Nigeria
and Ghana: in the space of 11 years, both countries boosted yields by
25 percent, to around 15 tonnes per ha10.
Average yields in the rest of the region remain low, at around
10 tonnes. However, thanks to more intensive production – mainly
through greater use of improved varieties, mineral fertilizer and
other inputs – yields have increased substantially in some countries.
For example, a government programme in Malawi for the rapid
multiplication of disease-free, higher-yielding planting material led
to a rapid increase in cassava cultivation nationwide15. Between 1990
and 2011, average yields rose from 2.3 tonnes per ha to 21.5 tonnes,
and production from 144 000 to 4.2 million tonnes10.
10 Save and Grow: Cassava
More recently, Rwanda has shown how intensification can produce
spectacular results in a very short time. Since 2007, the country’s food
crop intensification programme has distributed to farmers 140 million
stem cuttings of improved, disease-resistant varieties, and provided
them with imported fertilizer and extension advice. As a result, yields
rose from less than 6.5 tonnes in 2007 to 12.3 tonnes by 2011, and
production more than tripled, from 780 000 to 2.5 million tonnes16.
Sub-Saharan Africa lags behind global trends in the development of
the cassava value chain. However, new uses for cassava are emerging:
in commercial livestock feed, as a partial substitute for wheat flour in
bread making and as an industrial raw material. In 2012, Nigeria made
a strong entry into the global cassava trade when it secured an order
to supply China with 1 million tonnes of dried cassava chips10; the
government recently announced further sales to China of 3.3 million
tonnes in 201317.
Asia
Cassava growers in Asia account for 30 percent of world production.
Over the past three decades, their cassava output has grown by
66 percent, from 45.9 million tonnes in 1980 to 76.6 million tonnes in
2011. That growth was due almost entirely to more intensive cultivation – the harvested area in 1980 and 2011 was unchanged, at around
3.9 million ha, while average yields increased from 11.8 to 19.5 tonnes
per ha in the same period (Figure 3).
As in Africa, cassava is mainly a smallholder crop that was once
grown as a reserve in case of shortfalls in the rice harvest and as
on-farm animal feed18. Today, most cassava is grown in the region
to meet demand for dried cassava chips and cassava starch for use in
commercial livestock feed and for industrial processing.
Thailand put cassava on the map of industrial uses in the 1980s,
when it developed a thriving business exporting dried pellets to Europe
for use in livestock feed. The country’s impressive increase in cassava
production, from 3.4 million tonnes in 1970 to more than 20 million
tonnes in 1990, was achieved thanks to expansion of the harvested
area, which grew almost seven times over; yields actually fell, from
15.3 tonnes to less than 14 tonnes per ha10.
In the 1990s, Thailand launched a major programme for the dissemination to farmers of new, higher-yielding varieties, along with
improved access to mineral fertilizer and extension. Between 1990 and
Chapter 1: Cassava, a 21st century crop 11
2009, Thai yields rose by almost two-thirds, the harvested area shrank
by 10 percent, and production reached a record 30 million tonnes.
Since 2000, Asia’s cassava production has increased by 55 percent,
as more countries seek to enter lucrative export markets. The region’s
major customer is China. Between 2000 and 2009, China’s annual
imports of dried cassava grew from 256 000 tonnes to more than
6 million tonnes, while imports of cassava starch more than doubled,
to 1.2 million tonnes10.
Thailand dominates the export trade, shipping 6 million tonnes of
dried cassava chips and starch, with a total value of US$1.5 billion, in
2010. However, it faces increasing competition. Viet Nam has more
than quadrupled cassava production, from 2 million to 8.5 million
tonnes11 since 2000, and exported 1 million tonnes of dried cassava
in 2010. Indonesian exports also grew, from 150 000 tonnes in 2000
to 1.4 million tonnes. In Cambodia, a fledgling export trade in dried
cassava, amounting to 22 000 tonnes in 2011, was recently boosted
by orders from China for 1 million tonnes19.
An important new area of cassava utilization in Asia is as feedstock
for the production of biofuel – one tonne of dried chips yields about
300 litres of 96 percent pure ethanol13. As countries seek to reduce
both dependence on imported oil and greenhouse gas emissions,
companies in China, Japan and the Republic of Korea are obtaining
concessions for large-scale cassava plantations, mainly in Cambodia,
Indonesia, Lao PDR and the Philippines, as a source of dried chips for
ethanol production.
In a few countries, cassava remains first and foremost a food crop.
Indonesia has the region’s highest per capita cassava food supply, of
44 kg per year, well above the regional average of 6.7 kg. Cassava is
also grown mainly for food in Kerala State, India, where farmers have
achieved average root yields of 24 tonnes per ha, thanks to intensive
production, often under irrigation20.
Latin America and the Caribbean
Only 14 percent of the world’s cassava, or some 34.3 million tonnes, is
grown in Latin America and the Caribbean, where Manihot esculenta
was domesticated. Between 1980 and 2011, the harvested area grew by
less than 1 percent, to 2.6 million ha, while production increased by
15 percent, thanks to modest improvements in yields. Nevertheless,
average annual growth in production since 2000 has been at twice
the rate recorded in the previous two decades (Figure 4).
12 Save and Grow: Cassava
As in other tropical regions, cassava in the Americas is usually
relegated to marginal areas with uncertain rainfall, acid soils, low
native soil fertility, and difficult terrain. The inherent nature of cassava
cultivation, especially the labour inputs required, makes it generally a
smallholder crop, grown in farming systems that include other crops
or animal components21. Production is dominated by Brazil, which
harvested 24.4 million tonnes – almost three-quarters of the region’s
total output – in 2011, followed by Paraguay (2.4 million tonnes),
Colombia (2.2 million tonnes) and Peru (1.1 million tonnes)10.
Although consumption of cassava as food has declined over the past
50 years, with the massive movement of rural populations to urban
areas, it remains an important staple food especially in Colombia and
northeast Brazil. FAO estimates that, regionally, about half of cassava
production is used as food and half as animal feed. Cassava consumption is being promoted in Brazil by policies aimed at substituting
imported cereals with domestically produced cassava flour. The
government has mandated the blending of 10 percent cassava flour
with wheat flour in bread, an initiative that is estimated to absorb
about half of the country’s cassava output11.
Cassava growers in Latin America and the Caribbean typically
apply few inputs, and yields – averaging 12.9 tonnes per ha – are well
below potential levels. However, there has been a significant shift,
beginning in the 1990s, toward larger-scale, more intensive production,
especially in Brazil. While most of Brazil’s cassava continues to be
grown in the dry northeast, where yields average around 11 tonnes per
ha21, intensive cultivation in the country’s southern states – mainly to
produce cassava flour and native starch for the food, cardboard and
textile industries – has obtained yields of up to 40 tonnes22.
Brazilian production of cassava starch, processed mainly in factories
in the state of Paraná, is estimated at more than 500 000 tonnes in
201123. Some 70 percent of the raw material is produced by smallholder
farmers24. To ensure a year-round supply of raw material, cassava
production is mechanized, with farmers frequently cultivating cassava
as a monocrop using high levels of inputs24. Other countries in the
region, notably Colombia, Paraguay and Venezuela, are also increasing
their capacity to produce cassava starch. Compared to Asia, very little
of the region’s cassava output enters international trade. In fact, the
biggest exporter is Costa Rica, which exported some 92 000 tonnes
of dried cassava in 2010.
Chapter 1: Cassava, a 21st century crop 13
Although world cassava production reached record levels in 2012,
for the 14th consecutive year, there remains ample room for further
growth. World trade in cassava products saw a marked expansion in
2012, thanks to cassava’s price advantage over maize as a source of
starch. International prices of chips and starch have been remarkably
stable, despite very strong demand. FAO expects continued increases
in production in 2013 in sub-Saharan Africa11.
Cassava’s new status in agriculture is a major step forward toward
realization of Global Cassava Development Strategy, adopted in 2001,
after four years of consultations, by FAO, the International Fund for
Agricultural Development (IFAD), public and private sector partners
and 22 cassava-producing countries. The strategy recognized cassava’s
potential not only to meet food security needs, but also to provide an
engine for rural industrial development and a source of higher incomes
for producers, processors and traders25.
If anything, growth in cassava production is likely to accelerate
over the current decade. Once seen as the “food of the poor”, cassava
has emerged as a multipurpose crop for the 21st century – one that
responds to the priorities of developing countries, to trends in the
global economy and to the challenges of climate change. In brief:
Rural development. Policymakers in tropical countries are recognizing the huge potential of cassava to spur rural industrial development
and raise rural incomes. They look to Thailand, where increases in
yields over the past two decades have boosted smallholder earnings
by an estimated US$650 million and lifted many cassava growers
out of poverty. In southern Brazil, cassava is a multi-million dollar
industrial crop, processed in factories that employ thousands of rural
people24. It has been estimated that investments in cassava research
and development in Africa could generate some of the highest gains
in agricultural GDP26.
Urban food security. A major driver of production increases will be
high prices of cereals on world markets, which sparked global food
price inflation in 2008. In Africa, persistent urban poverty has boosted
the consumption of cassava food products as consumers seek cheaper
sources of calories12. Among FAO’s recommendations to governments
for holding down food prices is processing cassava into products that
are marketable as instant foods with a long shelf-life27. Cassava could
also help improve the nutrition of low-income populations – new
14 Save and Grow: Cassava
biofortified varieties produce roots that are rich in vitamin A, iron
and zinc.
Import substitution. Many governments have, or are considering,
mandatory blending of mostly imported wheat flour with domestically
produced cassava flour in bread making. Nigeria recently raised its
levy on wheat flour to 100 percent, and will use revenue for a cassava
bread development fund11. It has also announced plans to substitute
10 percent of the maize in poultry feed with cassava grits, which will
increase annual demand for cassava roots by 480 000 tonnes28. In
East Africa, the animal feed industry is turning to cassava, as maize
and wheat become increasingly unaffordable29.
Renewable energy. Global output of bio-ethanol could reach 155 billion litres by 2020, up from around 100 billion litres in 2010. Cassava
currently contributes to only a small part of production, but demand
from China is growing rapidly following its decision to no longer use
cereals to produce biofuel. Currently, 50 percent of China’s ethanol
is derived from cassava roots and sweet potatoes, and in 2012 it was
expected to produce 780 million litres of ethanol from 6 million
tonnes of dried cassava13. China plans to develop cassava varieties
suitable for biomass energy production in colder and drier regions of
the country’s north30.
New industrial uses. Worldwide, cassava is the second biggest source
of starch, after maize, with production estimated at 8 million tonnes a
year. However, tropical countries import each year some US$80 million worth of maize starch that could be replaced by starch from locally
grown cassava13. In Thailand, which has earned some US$4 billion
from starch exports since 2000, scientists are developing a variety
with root starch that rivals premium “waxy” maize starch31, 32. A
recent cassava mutation offers smaller root starch granules that reduce
considerably the time and energy required for ethanol production33.
Adaptation to climate change. Another factor that favours increased
cassava production is the crop’s potential to adapt well to climate
change. A recent study of the impacts of climate change on major
staple crops in Africa found that cassava was the least sensitive to the
climatic conditions predicted in 2030, and that its suitability would
actually increase in most of the 5.5 million sq km area surveyed.
Chapter 1: Cassava, a 21st century crop 15
Conversely, all other major food crops in the region, including maize,
sorghum, millet, beans, potatoes and bananas, were expected to suffer
largely negative impacts34.
As market demand grows, traditional cassava cropping systems are
being replaced worldwide by more intensive production. In the years
ahead, the trend towards intensification – aimed at achieving higher
yields on the same area of land – is expected to strengthen in all
cassava-producing regions. The alternative, expanding the harvested
area, is not feasible in most countries owing to a diminishing supply
of arable land and the high labour requirements of cassava cultivation. Past experience has also demonstrated that opening up new
areas for cassava can carry heavy environmental costs: in Thailand,
expansion of the harvested area in the 1970s and 1980s led to massive
deforestation25.
Farmers, industry and policymakers are seeking solutions to
constraints to cassava yield increases9. Smallholder producers in
Brazil, India and Thailand have been highly successful in commercial
production, obtaining yields of between 25 and 40 tonnes per ha,
through more intensive farming. Although current African yields
are less than half the global potential yield, root harvests of up to
40 tonnes have been obtained in on-farm trials35. In Nigeria, yields
could reach 25 tonnes per ha and beyond with improved varieties,
agronomic practices and crop management.
Rwanda plans to boost its cassava output in 2017 from the current
2.5 million tonnes to as much as 6.1 million tonnes, by disseminating
higher-yielding varieties, training farmers in improved crop management, and encouraging increased use of mineral fertilizer, pesticide
and irrigation16. Supported by international donors, other African
countries – including Ghana and the Democratic Republic of the
Congo – have made similar plans for the commercialization of cassava,
in line with the African Union’s Pan-Africa Cassava Initiative, which
has identified Manihot esculenta as a key agricultural commodity,
food security crop and “poverty fighter”36.
The future of cassava is likely to see, therefore, a shift to increased
monocropping on larger fields, the widespread adoption of higheryielding genotypes that are more suited to industrialization, and higher
rates of use of irrigation and agrochemicals.
16 Save and Grow: Cassava
In promoting programmes for intensified cassava production,
policymakers should consider the lessons of the Green Revolution.
Based on genetically uniform crop varieties and intensive use of tillage, irrigation, mineral fertilizer and pesticide, the Green Revolution
model of agriculture produced a quantum leap in global cereal yields
and average per capita food consumption. But those enormous
gains in productivity were often accompanied by negative effects on
agriculture’s natural resource base, so serious that they jeopardize
its productive potential in the future. In many countries, decades of
intensive cropping have degraded fertile land and depleted groundwater, provoked pest upsurges, eroded biodiversity, and polluted air,
soil and water37.
Applying the same model to cassava production carries similar risks.
A shift from traditional smallholder cassava farming systems – based
on intercropping and periods of fallow to replenish soil nutrients39 – to
more intensive monocropping may simplify management and favour
initially higher yields. Experience has shown, however, that it also
increases the prevalence of pests and diseases, and accelerates the
depletion of soil nutrient stocks35, 38.
In southern Brazil, year-round demand for cassava for starch
processing has led to continuous monocropping in the same field,
overlapping planting dates, increasing use of genetically uniform
varieties, and greater need for agrochemicals to maintain soil fertility and combat pests and diseases24. In Rwanda, higher cropping
densities under intensification have created pest and disease pressure
that is negatively affecting yields16. As warmer conditions start to
favour intensive cassava production in new areas of Africa, Asia and
South America, the risk of pest and disease problems is expected to
increase24.
Continuous cultivation of cassava – involving at least 10 years of
production on the same piece of land with less than one year of fallow
between crops – is already widespread in sub-Saharan Africa, especially in non-humid and highland zones40. In East Africa, agricultural
landscapes have changed from traditional systems with an important
fallow component to continuous cassava-based production35.
With intensification, many of Africa’s cassava growers have eliminated fallow periods altogether and are not compensating for nutrient
losses by adopting soil fertility management techniques, such as cover
crops and manure application. Declining levels of soil nutrients lead to
falling yields, to the point where production becomes unprofitable39.
Chapter 1: Cassava, a 21st century crop 17
In northeast Thailand, several years of cassava cultivation in upland
areas led to a decline in soil fertility owing to erosion, tillage practices
that removed soil cover, and the failure of farmers to incorporate
residues in the soil41. In Colombia, yields of monocropped cassava
dropped from 37 tonnes to 12 tonnes per ha over a period of nine years
owing to soil degradation.
In Nigeria, research found that soil erosion increases when
traditional mixed cropping is replaced by monoculture42. Moreover,
traditional practices, found to be highly successful in reducing soil
erosion under polyculture, are less effective when used in monoculture42. In trials in Viet Nam, monoculture of cassava produced yields
of 19 tonnes, but resulted in severe, unsustainable soil losses to erosion
of more than 100 tonnes per ha43.
In 2010, FAO endorsed an ecosystem-based approach to crop
production intensification, one that is both highly productive and
environmentally sustainable44. Dubbed “Save and Grow”, it calls for
“greening” the Green Revolution through farming practices that draw
on nature’s contributions to crop growth, such as soil organic matter,
water flow regulation, pollination and bio-control of insect pests and
diseases. The key principles underpinning “Save and Grow” are:
 maintaining healthy soil to enhance crop nutrition
 cultivating a wider range of crop species and varieties in associations, rotations and sequences
 using well-adapted, high-yielding varieties and good quality seed
 efficient water management that produces more crops per drop
 preventative management of insect pests, diseases and weeds.
This eco-friendly model of agriculture encourages reduced or
zero-tillage in order to boost yields while restoring soil health. It
controls insect pests by protecting their natural enemies rather than by
spraying crops indiscriminately with pesticide. It uses mineral fertilizer
sparingly, in combination with organic sources of soil nutrients37.
Supporting evidence from agricultural development projects in
57 developing countries has shown that more efficient use of water,
reduced use of pesticide and improvements in soil health boost crop
yields by around 80 percent45. Another study concluded that farming
systems that conserve ecosystem services, through conservation
tillage, crop diversification, legume intensification and biological pest
control, perform just as well as high-input intensive systems46, 47.
With “Save and Grow”,
tropical countries
can avoid the risks of
intensified cassava
production
18 Save and Grow: Cassava
This guide shows how “Save and Grow” can help developing
countries avoid the risks of unsustainable intensification, while realizing cassava’s potential for producing higher yields, alleviating rural
poverty and contributing to national economic development. It shows,
for example, how growing cassava with groundnuts produces not only
high root yields but also much higher income than monocropping;
how a predatory wasp has been far more effective than insecticide in
defeating devastating outbreaks of cassava mealybug; and how rotating cassava with beans and sorghum restored yields where mineral
fertilizer alone had failed.
Chapters 2, 3, 4, 5 and 6 present a set of adoptable and adaptable
ecosystem-based practices that have enhanced cassava productivity
and can serve as the cornerstone of national and regional programmes.
Chapter 7 explores post-harvest uses and value addition. Chapter 8
outlines policies that facilitate sustainable intensification of cassava
production, and underlines the importance – when introducing new
practices or technologies – of “letting farmers decide”.
Chapter 2
Farming systems
Many smallholder cassava growers
already practise key “Save and Grow”
recommendations: reduced or zero
tillage, protecting the soil surface
with organic cover, and crop
diversification.
Chapter 2: Farming Systems 21
I
n “Save and Grow”, farming systems are founded on three key
recommendations1. First, farmers should aim at protecting soil
structure, soil organic matter and overall soil health by limiting
mechanical disturbance of the soil. That means minimizing
“conventional tillage”, the practice of ploughing, harrowing or hoeing
land before every crop and during crop growth. Instead, farmers are
encouraged to practise conservation tillage, which excludes operations that invert the soil and bury crop residues. Common forms of
conservation tillage are strip or minimum tillage, which disturbs only
the portion of the soil that is to contain the seed row or planting hole,
and zero tillage, in which ploughing or hoeing are eliminated.
Along with conservation tillage, FAO recommends maintaining
a protective organic cover on the soil surface, i.e. using crops and
mulches to reduce soil erosion, conserve soil water and nutrients, and
suppress weeds. Organic soil cover not only improves soil’s physical
properties; it also encourages the proliferation of soil biota – including
earthworms and beneficial protozoa, fungi and bacteria – that promote
soil health and crop performance. In zero tillage systems, crops are
planted directly through a mulch formed by the residues of previous
crops or cover crops.
Third, farmers should cultivate a wider range of plant species in
associations, sequences and rotations that may include trees, shrubs
and pasture. Mixed cropping diversifies production, which helps
farmers to reduce risk, respond to changes in market demand and
adapt to external shocks, including climate change. Rotating or associating nutrient-demanding crops with soil-enriching legumes, and
shallow-rooting crops with deep-rooting ones, maintains soil fertility
and crop productivity and interrupts the transmission of crop-specific
pests and diseases.
By improving levels of soil organic matter and biotic activity,
reducing pest and disease pressure, reducing erosion and increasing
the availability of crop water and nutrients, those three practices
increase yields sustainably. They also lower production costs, mainly
through savings on machinery, fossil fuel and external inputs such as
irrigation, mineral fertilizer and pesticide.
22 Save and Grow: Cassava
To till or not to till?
C
assava needs a sufficiently loose-textured soil to facilitate
initial root penetration and to allow for root thickening. It also
succumbs easily to weed competition, excessive soil moisture and
root rot. For those reasons, it is usually planted in soil that has been
loosened and cleared of weeds by hoeing or ploughing. On degraded
and unstructured soils, conventional tillage makes it easier to insert
stakes in the ground and provides well-drained, aerated conditions
for the root system2, 3.
However, crop yields are a function not of tillage, but of soil conditions. Cassava stakes can also be planted, and can produce good yields,
in soil that has not been tilled, provided that the soil is healthy, well
structured and free of compaction4. Friable soils, high in organic
matter, provide ideal conditions for zero-till cultivation2. A study of
smallholder cassava production in East and West Africa found that
cassava was more frequently planted on seedbeds without prior land
preparation than any other staple crop, except rice. Where soils had
poor physical properties, farmers planted it on manually prepared
mounds or ridges5.
Continuous conventional tillage, especially when done with heavy,
tractor-mounted ploughs, harrows and rototillers, buries the soil’s
protective cover, kills soil biota, causes the rapid decomposition of
organic matter, and degrades soil structure by pulverizing soil aggregates. Ploughing or hoeing the soil at the same depth, season after
season, often leads to the formation of a hardpan, a compacted soil
layer – usually found below the topsoil – that is difficult for water and
roots to penetrate6. In such soils, some kind of mechanical loosening
will be necessary for continued crop production, but at the cost of
further soil degradation.
In that same soil, growing cassava without tillage may produce lower
yields in the initial years. In the longer term, however, by reducing
mineralization, erosion and water loss, helping to build up organic
matter and maintaining soil aggregate stability and internal drainage,
zero tillage promotes root functioning to the maximum possible
extent. Once soil health is restored, untilled land can produce high
yields and do so at a lower cost to both the farmer and the farming
system’s natural resource base7-10.
Chapter 2: Farming Systems 23
Currently, land is prepared for cassava in many different ways and
at different intensities. Small-scale farmers in Indonesia, Viet Nam
and many African countries, or wherever land is too steep for any
kind of mechanization, usually use a hoe to loosen soil in the area
to be planted. Since manual land preparation is labour-intensive,
many farmers prepare only the planting hole itself. While that is a
form of reduced tillage, it can also result in low yields if weeds are
not controlled.
In regions where farmers cultivate larger areas of cassava, they
traditionally plough the fields with oxen or water buffaloes, usually
in one or two passes. In mountainous areas of Colombia, farmers use
a pair of oxen pulling a simple reversible plough11. In Indonesia, they
plough the field with oxen, and then create planting ridges by hand,
using a short-handled hoe. In Kerala State, India, farmers hoe the soil,
then make individual mounds for each cassava plant, a labour intensive
approach requiring more than 30 days of labour per hectare.
In countries where cassava is grown intensively on larger areas, of
from 2 to 5 ha, land is usually prepared by tractor using a mouldboard
or disc plough, generally followed by the use of a disc harrow and
sometimes a ridger. Alternatively, the soil is loosened and residues and
weeds are incorporated with a rototiller. However, this method tends
to pulverize the soil and can lead to serious erosion on sloping land.
Many cassava farmers in southern Brazil practise conservation
tillage. They generally grow a cover crop, such as black oats (Avena
strigosa) or wheat, during the winter months to protect the soil surface,
increase soil organic matter and suppress weeds. In the spring, before
the cereal crop matures, they crush it with a tractor-drawn rolling
drum, or kill it with herbicides, then plant cassava stakes with a
mechanized planter directly through the mulch of the crop’s residues.
In Paraguay, farmers practise hand-planting of cassava without tillage
using black oats or leguminous shrubs as a winter cover crop12.
Many experiments have attempted to determine the best method
of land preparation for cassava and the effectiveness of conservation
tillage alternatives11, 13. However, evidence of the effect of different
tillage options on yields is not conclusive: the results of trials in Africa,
Asia and Latin America vary from year to year and from place to
place. On a gentle slope in Colombia, reduced tillage – involving the
preparation by hoe of the planting holes only – resulted in the highest
yields of one variety, while the use of a tractor-mounted rototiller
24 Save and Grow: Cassava
produced the highest yields of another
variety (Figure 5). Both zero tillage and
strip preparation with a hoe or rototiller
Variety B
produced significantly lower yields. But
other trials in the same area – which
compared zero tillage, ploughing with
oxen, and strip tillage – found that zero
tillage produced the highest yields as well
as the lowest rates of soil erosion.
In a three-year experiment on a 25 percent slope in Hainan Province, China, the
highest yields, of 26 tonnes per ha, were
obtained by conventional ploughing and
disking. Reduced tillage of the planting
Rototiller
Reduced
Zero
holes produced slightly lower per hectare
tillage
tillage
yields, of 24.6 tonnes, while zero tillage
and strip preparation produced lower yields still, of around 22.8 tonnes.
However, zero and reduced tillage also resulted in the lowest rate of
soil erosion, which was a major problem on the steep slopes14.
In Brazil, average cassava yields over four years of trials were
18.2 tonnes per ha on zero-tilled plots, significantly lower than the
24.7 tonnes obtained with conventional tillage15. However, in clay
soil that had been previously planted with winter maize under zero
tillage for four years, there were no significant differences between
zero tillage and conventional tillage yields16.
In a land preparation trial conducted for four consecutive years
in Thailand, the standard practice – ploughing twice with a 3-disc
plough followed by a 7-disc harrow – produced the highest yields,
while zero tillage consistently produced the lowest yields3. In another
Thai experiment, however, tillage did not result in significant yield
differences. Using a subsoiler followed by a chisel plough, researchers
obtained an average root yield of some 22 tonnes per ha, compared
to 20 tonnes when the land was not tilled and weeds were controlled
with herbicide17.
Also in Thailand, with nitrogen fertilizer applied at the rate of
100 kg per ha, the fresh root yield of cassava grown under zero tillage
reached 67 tonnes, significantly higher than the 53 tonnes obtained
using conventional tillage (Figure 6). In the second year, average yields
from the unprepared plots fell to 49 tonnes, slightly less than the
conventional tillage yield that year of 54 tonnes17.
Figure 5 Effect of tillage system on cassava root yield,
Colombia (t/ha)
20
Variety A
15
10
5
0
Strip
tillage
Source: Annex Table 2.1
Chapter 2: Farming Systems 25
A study in Nigeria found that yields under con- Figure 6 Effect of tillage system
ventional ridge tillage were up to 46 percent higher and fertilizer* on cassava root yield,
than those obtained in untilled fields18, although zero Thailand (t/ha)
tillage was practised by the majority of local farmers. 80
Conventional tillage
Zero tillage
However, the trial beds were planted at the height of
70
the rainy season in June, when levels of soil moisture
were higher and soil temperatures lower, which delayed 60
the emergence of plants in the zero-tilled plots and led 50
to a substantial number of rotten stems18. In fact, when 40
planted at the onset of the rainy season, in March,
cassava emergence was higher under zero tillage19. 30
Other trials in Cameroon and Nigeria have found that 20
cassava yields were not affected by tillage18, 20; in the 10
Democratic Republic of the Congo, yields were higher
in untilled than tilled oxisols, and similar in sandy 0
0-50-50
50-50-50
100-50-50
loam soil, provided the field was mulched2.
* N-P2O5-K2O in kg/ha
Finally, a recent study of an 8-year experiment in
Source: Annex Table 2.2
sandy loam soil in Colombia concluded that zero
tillage was more effective in building up
Figure 7 Cassava yield response to surface
soil nutrients and conserving the soil’s plant mulch, fertilizer and tillage, Colombia (t/ha)
physical properties and, when combined 7
with mulching of residues, produced the
Fertilized
Unfertilized
highest root yields, with or without min- 6
eral fertilizer (Figure 7). Weighing up the 5
costs and benefits, the study concluded
that zero tillage compared favourably 4
with conventional tillage and, in the 3
long term, was “an optimum system” for
2
cassava production21.
1
Based on the evidence presented, no
single method of land preparation can 0
Conventional Conventional
be described as “best for cassava”. As a
tillage
tillage+mulch
general conclusion, it can be inferred
Source: Annex Table 2.3
that the effects of tillage on cassava yield
are variable from year to year and that the benefits of zero tillage in
terms of erosion control are usually positive. Research also indicates
that some land preparation is necessary in areas with heavy, poorly
drained soils or where soils are already badly degraded. However, even
in those cases, the need for tillage can be reduced through practices
Zero
tillage
Zero tillage
+mulch
26 Save and Grow: Cassava
that improve soil structure, organic matter content and drainage,
such as mulching2.
Cassava growers should be encouraged to adopt minimum tillage
and, ideally, zero tillage, especially on well-aggregated, friable soils
with an adequate level of organic matter. Since yields do not depend
on tillage per se, but on soil health, it is also recommended that, in
tillage trials, changes in soil structure and organic matter under a
zero-till regime be monitored closely, as those factors are likely to have
a long-term positive impact on cassava yields and are good indicators
of sustainability.
Even where conservation tillage produces lower yields, it offers
farmers economic advantages: reduced spending on the fuel and
equipment needed for conventional tillage, and – since it reduces soil
erosion, conserves soil moisture and helps maintain soil health – the
opportunity to produce cassava more intensively and sustainably,
without the need for high levels of external inputs22. Conservation
tillage will also be important as an alternative to conventional tillage
in cassava-growing areas affected by climate change. Where rainfall is
reduced, it will help to conserve soil moisture; where rainfall increases,
it will help reduce soil erosion and improve soil structure, allowing
better internal drainage23.
Cover crops and mulching
M
aintaining a continuous ground cover is another basic “Save
and Grow” practice that is also essential for reaping the full
benefits of conservation tillage. Ground cover is especially important
in cassava production – because the initial growth of cassava is slow,
the soil is exposed to the direct impact of rain during the first 2 to
3 months of its growth cycle, and the wide spacing between planted
stakes favours the emergence of weeds. To protect the soil surface,
reduce runoff and erosion, and inhibit weed growth, “Save and Grow”
recommendations include covering the soil surface with mulch, such as
crop residues, or growing cover crops (also called “live mulch”) during
fallow periods or during cassava establishment. Mulching seedbeds
is recommended especially when growing cassava on slopes prone to
soil erosion. Cassava stakes can be planted directly through the mulch
cover, with little or no land preparation24.
Chapter 2: Farming Systems 27
Mulch cover also serves as an insulating layer that reduces diurnal
temperature variations and water evaporation, even during periods
of prolonged drought. It increases the soil organic matter content
and provides a favourable environment for soil micro-organisms and
below-ground fauna. By improving physical soil conditions – reduced
soil temperatures, higher levels of moisture, increased water infiltration capacity and lower evaporation – it favours higher yields16.
In a 3-year trial in the Democratic Republic of the Congo, the
application of 5 tonnes of rice straw on late season cassava led to
an increase in soil pH, organic carbon content, total nitrogen, soilavailable phosphorus and soil exchangeable cations. Mulched cassava
plants produced more and bigger storage roots than unmulched plants,
and the dry storage root yield increased
Figure 8 Effect of mulching on dry root yield of late season
each year, from an average of 4.3 tonnes cassava, Democratic Republic of the Congo (t/ha)
to 5.6 tonnes per ha, irrespective of 6
the cultivar used. In the first, second
Mulched*
and third year, yields were 17 percent, 5
Unmulched
28 percent and 58 percent higher, respectively, than those of unmulched 4
cassava (Figure 8)25.
Growing cover crops between cas- 3
sava cropping cycles is regarded mainly 2
as a soil improvement practice (see
Chapter 5, Crop nutrition). However, 1
it can also help reduce weed infestations. Fast-growing legumes smother 0
* rice straw at 5 t/ha
Year 1
Year 2
Year 3
many unwanted weeds that normally
Source: Annex Table 2.4
proliferate during cassava establishment
and after the cassava harvest, thus providing weed control that is
less labour-intensive than manual weeding and less expensive than
spraying with herbicides (see also Chapter 6, Pests and diseases).
Trials have found that while perennial legumes are more effective
for soil protection than commonly intercropped grain legumes, such
as beans and cowpeas, highly productive perennials, such as stylo
(Stylosanthes guianensis) competed strongly with cassava for nutrients
and reduced root yields considerably. However, with less aggressive
legumes, such as pintoi groundnuts (Arachis pintoi), the yield loss
was less serious26.
28 Save and Grow: Cassava
Mixed cropping
A
When grown as a
monocrop, cassava is
usually planted with
spacing of 1 m, making
10 000 plants per hectare
lthough cassava is widely grown as a monocrop in Thailand and
southern Brazil, intercropping is practised by smallholder cassava
farmers in many parts of the tropics. Subsistence growers, or those
with very limited areas of land, generally plant the space between
cassava rows with early maturing crops, such as maize, upland rice and
various types of grain legumes, including common beans, cowpeas,
mungbeans and groundnuts. The practice has many benefits – it
protects the soil from the direct impact of rain, reduces soil erosion
from runoff, and limits weed growth during the early stages of cassava
development.
Intercropping also produces crops that can be harvested at different
times during the year, increases total net income per unit area of land,
and reduces the risk of total crop failure. In south-western Nigeria,
for example, maize and cassava are often planted in the first of two
annual rainy seasons; the maize is harvested during a short break in
the rains, after which the cassava continues alone. Since the two crops
have different pest and disease complexes and growth requirements,
one may survive even if the other fails. Some farmers even plant a
second maize crop – cassava is less risky and the maize, if it succeeds,
provides a bonus27.
Chapter 2: Farming Systems 29
Growing cassava with short-duration grain legumes has an added
advantage: it supplies both carbohydrates and protein, which provide
the foundation of a healthy diet for the farming household. It has
been estimated that one hectare of cassava intercropped with black
common beans (Phaseolus spp.) can produce around 10 tonnes of
fresh cassava roots with 30 percent starch and 600 kg of beans with
28 percent protein – enough to meet the annual requirements of five
adults and leaving a surplus of about 6 tonnes of cassava for use as
animal feed or for sale2.
In many parts of Africa, cassava is grown with a wide range of other
crops, either in a regular pattern or an irregular mixture of various
crops that are continuously harvested and replanted as space becomes
available. In West Africa, farmers often plant from 5 to 10 cassava
stakes along the edge of large mounds, and plant crops such as maize,
beans and melons in the middle of the mounds.
In Indonesia, upland rice is grown between the cassava rows, while
maize is grown between the cassava plants in the rows themselves.
Once the rice and maize are harvested, at about four months after
planting, the inter-row space is replanted with grain legumes, such as
soybeans and groundnuts. In some areas, the long rainy season allows
the planting of a fourth intercrop, such as mungbeans, after the grain
legumes have been harvested. That very intensive intercropping allows
the production of up to five crops a year on a very small area of land.
Trials in Viet Nam showed that cassava intercropped with groundnuts (Arachis hypogaea) produced not only high root yields, of
30.7 tonnes per ha, but also much higher income than monocropping
In Indonesia, farmers
plant cassava along with
faster growing crops, such
as maize and rice. After
the cereal harvest, they
plant groundnuts
30 Save and Grow: Cassava
(Figure 9). At 32 tonnes per
ha, monoculture yields were
slightly better than those
Net income
Gross income
of the cassava/groundnut
system and production
costs were almost 30 percent lower. However, the
high commercial value of
the groundnut yield, of
1.5 tonnes per ha, resulted
in a total net income 50 percent higher than that of the
monoculture.
In the Democratic
Republic of the Congo,
planting cassava with spacCassava+mungbean
Monoculture
ing of 2 m between rows
and 0.5 m within the row
(instead of the usual 1 m x 1 m) allowed for two successive legume
intercrops, of groundnuts and climbing beans. The crop arrangement
did not affect the cassava root yield, and the extra income generated
from legume sales amounted to almost US$1 000 per ha28. In India,
intercropping with banana produced higher cassava root yields, while
the highest net return was obtained by combining cassava with french
beans or cowpeas29.
In northeast Thailand, dairy farmers have developed a “food-feed”
system of cassava intercropped with cowpeas. The cowpea crop
produces up to 2.4 tonnes of fodder per ha, which is fed along with
dried cassava leaves to their cows. While the system produces generally
lower root yields, compared with monocropping, researchers found
that it increased land use efficiency and resulted in higher economic
returns30.
Intercropping requires careful selection of the crops – and the most
suitable varieties of each crop – to be planted, careful timing of planting, good fertilization, and optimum plant densities and distribution.
In Nigeria, the success of maize/cassava combinations depends on the
time and the rate of recovery of the cassava after the maize harvest.
Research found that cassava root yields dropped from 31.6 tonnes per
ha to less than 20 tonnes with high densities of maize planting and
maize yields that exceeded 3.5 tonnes27. In trials in Thailand, planting
Figure 9 Production costs and income of three intercropping trials
with cassava, Viet Nam (million dong)
Production costs
30
25
20
15
10
5
0
Cassava+groundnut
Source: Annex Table 2.5
Chapter 2: Farming Systems 31
cowpeas (Vigna unguiculata) and sword beans (Canavalia gladiata)
at the same time as cassava, over a period of four years, resulted in
lower yields than when cassava was grown alone. However, moving the
planting date three weeks after that of cassava reduced competition
during cassava’s early growth stages, which allowed it to establish
better and produce root yields exceeding those of the monocrop31.
The effectiveness of intercrops in reducing soil erosion depends
on whether they have been able to produce enough foliage in time
to protect the soil surface from rainfall. That may explain why
experience with intercropping as a means of soil erosion control is
mixed. Intercropping with groundnuts, pumpkins, squash or sweet
corn was judged not very effective in Thailand, but growing cassava
along with maize in Viet Nam and with mungbeans in Thailand was
“quite effective”32.
More consistent results in reducing soil erosion have been achieved
by planting cassava with protective hedgerows, or “live barriers”, a
low-cost alternative to engineered soil conservation options such as
contour bunds or bench terraces33. Hedgerows filter and slow the rate
of runoff and can be created using various recommended grasses,
perennial legumes and other plants, or established naturally from
native grasses and other species left as unhoed or unploughed strips in
the field2, 34. Farmers in several Asian countries protect their fields with
hedgerows of vetiver grass (Vetiveria zizanioides), the shrub Tephrosia
candida, the grass Paspalum atratum and closely-spaced pineapple.
Vetiver grass, especially, is recommended for reducing severe erosion
of already degraded land.
An added advantage of planting hedgerows is that, when pruned
regularly, they provide in situ mulch, which makes these systems particularly effective in reducing erosion and less laborious than carrying
mulch from elsewhere. Pineapples can be harvested and sold, while
paspalum and other grasses can be cut and fed to cattle and buffaloes.
In trials in Viet Nam, monoculture of cassava without hedgerows
produced yields of 19 tonnes per ha, but resulted in severe soil losses of
more than 100 tonnes per ha. Intercropped with groundnuts, cassava
root yields were slightly higher and soil losses fell to 65 tonnes, a big
improvement but unsustainable in the long term. Cassava grown with
groundnuts and vetiver hedgerows recorded the highest root yields,
of 23.7 tonnes, the lowest soil losses, of 32 tonnes, and the highest net
income of all the treatments tested (Figure 10).
In Thailand,
intercropping cassava
with cowpea (above)
results in generally lower
root yields, but enough
cattle fodder to produce
higher net income
32 Save and Grow: Cassava
Another type of intercropping is agroforestry, in which trees and
perennial shrubs are grown along with crops. In India, cassava is
grown under mature coconut palms and rubber trees35. Cassava
may also be planted in alleyways between rows of deep-rooting and
fast-growing leguminous trees, such as Leucaena leucocephala and
Gliricidia sepium. The foFigure 10 Yield and dry soil loss in response to crop management
liage is cut back regularly
treatments, Viet Nam (t/ha)
and the prunings are either
120
Cassava yield
Dry soil loss
incorporated into the soil of
the alleys or – in a zero-till
100
system – applied as mulch
before the cassava is planted.
60
Since the trees fix large
amounts of atmospheric ni40
trogen and their roots draw
nutrients from deeper soil
20
layers, the decomposition of
prunings fertilizes the alley
0
soil and boosts the yield of
Cassava
Cassava
Cassava
alley crops. In dryer climates,
monoculture
+groundnuts
+groundnuts
trees are deeper-rooting and
+vetiver hedgerows
thus compete less for water
Source: Annex Table 2.6
and nutrients than other intercrops. In agroforestry systems with
cassava, leaf cuttings from the forage legume Flemingia macrophylla
were found to have a particularly positive effect on root yield36. In
Benin, a combination of mineral fertilizer and the application of
3 tonnes per ha of pigeon pea (Cajanus cajan) mulch led to significant
root yield increases37.
While cassava is rarely rotated with cereals in cassava-growing areas
with poor soils and unpredictable rainfall, it is a common practice in
cereal-growing areas in parts of Africa, where cassava’s ample litter
falls and post-harvest residues are used by farmers to maintain soil
fertility. Maize yields benefit substantially from the nitrogen released
by the decomposition of green, leafy cassava biomass38.
In marginal areas where cassava is the main crop, it can be rotated
with grain legumes, such as beans, groundnuts, mungbeans, cowpeas
and soybeans, which fix atmospheric nitrogen and make it available to
the successive cassava crop. In India, sequential cropping of cassava
and cowpeas improved soil fertility to the point where applications of
Chapter 2: Farming Systems 33
manure and mineral fertil- Figure 11 Cost and benefit of sequential cropping with cassava
izer could be reduced by and cowpea, India (‘000 Rs/ha)
50 percent, with no yield
loss. Thanks to savings on
Production cost
Gross income
Net income
external inputs, income 90
from the cowpea-cassava 80
sequential cropping system 70
exceeded that of production 60
using full fertilizer treat- 50
ments (Figure 11)39.
40
A study in Colombia 30
found that yields of mono- 20
cropped, unfertilized cassa- 10
va dropped from 37 tonnes 0
No treatment
Half treatment
Full treatment*
to 12 tonnes per ha over a
period of nine years. While * Full treatment= 26 kg/ha P + 25 tonnes/ha farmyard manure
moderate use, thereafter, of Source: Annex Table 2.7
fertilizer had no positive effect on productivity, a rotational scheme
– using sunn hemp (Crotalaria juncea), maize, cassava, common
beans, sorghum and cassava again – restored yields to 30 tonnes.
Researchers concluded that soil nutrients were not deficient, but that
the cassava had been unable to make use of them owing to biological
soil degradation following years of continuous cassava production40.
In Thailand, a long-term experiment showed that rotating cassava
yearly with groundnuts, followed by pigeon peas in the same year,
contributed to a steady increase in cassava root yields, while yields
under continuous cassava monocropping tended to decrease31.
Many smallholder cassava production systems already incorporate,
to varying degrees, the three key “Save and Grow” practices of
minimizing soil disturbance, using organic soil cover and improving
system resilience through crop diversification and cropping sequences.
Those practices provide the foundation for sustainable intensification of cassava production. However, they need to be supported by
four additional “Save and Grow” practices: the use of well-adapted,
high-yielding varieties and good quality planting material; efficient
management of water resources; enhanced crop nutrition based on
judicious use of mineral fertilizer combined with organic manures;
and integrated management of insect pests, diseases and weeds. Those
practices are described in the following chapters.
Chapter 3
Varieties and
planting material
The full potential of cassava
will not be realized until production
constraints are mitigated in higheryielding varieties and cassava growers
have access to disease-free planting
material.
Chapter 3: Varieties and Planting Material 37
F
arming systems based on “Save and Grow” will use crops and
varieties that are better adapted to ecologically based production than those bred for high-input agriculture. More limited
use of external inputs will require plants that are more productive, use nutrients and water more efficiently, have greater resistance
to insect pests and diseases, and are more tolerant to drought, flood,
frost and higher temperatures.
Varieties will need to be adapted to less favoured areas and production systems, produce food with higher nutritional value and desirable
organoleptic properties, and help improve the provision of ecosystem
services. Sustainable intensification will also require adaptation to
climate change – greater genetic diversity will improve adaptability,
while increased resistance to biotic and abiotic stresses will improve
the resilience of cropping systems.
Farmers will need the means and opportunity to deploy those
materials in their production systems. That is why the management
of plant genetic resources, development of crops and varieties, and the
timely distribution of high quality seed are essential contributions to
sustainable intensification1.
Among the world’s major staple food crops, cassava is well-known
for its ability to produce reasonable yields on poor soils, in areas with
low or erratic rainfall, and without agrochemicals and other external
inputs. Those “hardy” traits have made cassava highly suitable for
low-input, small-scale agriculture, while its inherent potentials have
placed it among the crops most suitable for resource-poor farming in
the tropics and neotropics under 21st century climate change scenarios.
However, cassava’s full potential will not be realized until some
critical production constraints are mitigated in higher-yielding, welladapted varieties. For example, cassava is susceptible to waterlogging,
to low temperatures at high elevations, and to a wide spectrum of
mutable pests and diseases that can seriously affect yields. Climate
change models indicate that it will be affected more by biotic constraints than drought and high temperatures2.
With the growing importance worldwide of cassava as a source of
food, animal feed and industrial feedstock, there is increasing demand
for cultivars with specific characteristics and adaptation to different
ecologies. Niche varieties need to be developed and deployed to cater to
increasingly diverse and competing end uses. In Africa, new varieties
will be needed as cultivation expands into dry savannah, semi-arid and
38 Save and Grow: Cassava
subtropical zones and the shift towards market-oriented production
accelerates3.
The system that will provide high-yielding and adapted cassava
varieties to smallholders has three parts: genetic resources conservation and distribution, variety development, and the production and
delivery to farmers of high quality, healthy planting material.
Conserving the cassava genepool
T
he genus Manihot consists of the cultivated species, Manihot
esculenta, and – depending on the taxonomic classification used
– from 70 to 100 wild species4. Both wild relatives and traditional
cultivars, or landraces, developed by farmers over centuries are the
primary sources of genes and gene combinations for new varieties4.
In the early 1970s, CIAT launched a major initiative to collect
and conserve cassava landraces. Today, CIAT’s collection at Cali,
in Colombia, is the world’s largest, containing about 5 500 landrace
accessions. The collection is maintained in a tissue culture laboratory,
and a back-up in vitro collection is held at the International Potato
Center in Lima. CIAT has created a “core collection” of about 630
accessions that represents the wide genetic diversity found in the
main collection and is used for intensive characterization and genetic
analysis. A duplicate of the core collection is maintained in Thailand,
both in vitro and in the field.
The International Institute of Tropical Agriculture (IITA) in Ibadan,
Nigeria, also has an important cassava genebank of some 2 800 accessions, collected mainly in West Africa. The largest national collection,
of 2 900 accessions, is held by the Brazilian Agricultural Research
Corporation. Other major collections, totalling 7 200 accessions, are
held by Benin, India, Indonesia, Malawi, Nigeria, Thailand, Togo and
Uganda (Figure 12). Most other cassava-growing countries have established a genebank of local landraces and improved varieties, although
little documentation is available on many national collections4.
Over the past two decades, biotechnologists and molecular breeders
have used genebank accessions to determine which genes control
specific traits, and in 1997 the first genetic map of cassava was announced5. With the decreasing cost of molecular biology and biotechnology, the time is right to begin the genome-wide characterization
Chapter 3: Varieties and Planting Material 39
Figure 12 Major collections of cassava germplasm
(number of accessions)
6000
5000
4000
3000
2000
1000
o
To
g
in
d
Be
n
an
ai l
sia
Th
i
ne
law
In
do
a
Ma
nd
ria
Ug
a
ge
a
Ni
di
In
IIT
A
zil
Br
a
CIA
T
0
Source: Annex Table 3.1
of cassava genetic diversity and to fill gaps in germplasm collections
before valuable diversity is lost6.
Further collection of landraces needs to be carried out as farmers
abandon their traditional cultivars for improved varieties. For example,
CIAT’s genebank has limited representation from Central America and
no accessions from Suriname or French Guiana6. According to FAO’s
Second report on the state of the world’s plant genetic resources for food
and agriculture, priority countries for collecting in the Americas are
the Plurinational State of Bolivia, Brazil, Colombia, Haiti, Nicaragua,
Peru and the Bolivarian Republic of Venezuela; in Africa, collecting
needs to focus on the Democratic Republic of the Congo, Mozambique,
Uganda and the United Republic of Tanzania. Strategies for on-farm
conservation and management of landraces also need to be developed
to complement ex situ conservation4.
Wild relatives of cultivated cassava could make an important
contribution to the development of varieties suitable for sustainable
intensification under low-input regimes. However, wild Manihot
species have been poorly collected and poorly characterized and
evaluated, and many populations are threatened in their native
habitats6. Land clearing in Brazil has been most extensive in areas that
40 Save and Grow: Cassava
are the natural habitats of seven wild Manihot species which could
be a valuable resource for future breeding of cassava for semi-arid
environments. Deforestation of the Amazon Basin threatens forest
species of Manihot, and urbanization and agricultural expansion are
reducing the habitats of wild relatives native to Mesoamerica. Action
is urgently needed, therefore, to realize long-standing proposals to
create in situ reserves for wild Manihot4.
The harmonization of passport and evaluation data on genebank
accessions should also be a priority. Molecular biology tools, underpinned by robust information technology, would contribute to more
efficient data generation and dissemination, and facilitate global
genotyping of cassava accessions. Data should be made publicly available through searchable databases in order to facilitate the acquisition
of germplasm that could be used to augment locally available heritable
variations for the genetic improvement of the crop.
That is a major undertaking, and will require the active collaboration of CIAT, IITA, national programmes – particularly in the main
producing countries and the crop’s centres of genetic diversity – and
the advanced laboratories that work on cassava. Through multilateral
mechanisms, especially the International Treaty on Plant Genetic
Resources for Food and Agriculture, FAO can provide a much-needed
neutral platform for synergistic cooperation.
Breeding improved varieties
E
arly introductions of cassava from Latin America to Africa and
Asia represented a narrow genetic base, which limited the diversity
available to farmers for selection of new varieties. In Thailand, for
example, a single clone – Rayong 1 – was grown on 90 percent of
the entire cassava-cultivated area until the 1990s7. The availability
of superior varieties with combinations of many useful traits has
improved remarkably in recent decades, as researchers at CIAT, IITA
and several national breeding programmes have exploited the wide
genetic diversity available in genebanks.
The breeding and distribution of higher-yielding varieties with
resistance or tolerance to biotic and abiotic stresses have contributed
to substantial increases in cassava yields and to overall production –
especially in Asia – over the past 30 years. It is estimated that improved
Chapter 3: Varieties and Planting Material 41
varieties are planted on 55 percent of Asia’s total cassava farming area.
In Africa, the rate of adoption is lower, and in fact yields there are also
much lower. In order to close the yield gap, therefore, the dissemination
and adoption of improved varieties need to be promoted worldwide.
Higher yield and improved root quality are the most common
breeding objectives, but others also receive breeders’ attention, including resistance to insect pests and diseases, and tolerance to drought,
waterlogging, low and high temperatures, high soil acidity and low soil
phosphorus8-11. While some genebank accessions have been released
directly as new varieties, most are used in crossing programmes to
produce new varieties that combine high yield potential with other
beneficial traits.
The CIAT breeding programme has released clones with better
resistance to cassava bacterial blight, super-elongation disease, white
flies and thrips, and tolerance to root rot caused by Phytophthora water
moulds. It has also developed cold-tolerant varieties that produce well
in areas up to 1 800 m above sea level, such as the tropical Andes and
the East African highlands, and works with national programmes to
develop varieties adapted to the seasonally cool subtropics of China,
Brazil and Paraguay.
More than half a million sexual seeds produced by CIAT have
been distributed to national breeding programmes in Asia, which use
them to make selections or to cross the best selections with their own
promising lines. At least 50 improved varieties containing some Latin
American germplasm supplied by CIAT have been released in Asia.
Cassava plants have 3 to
11 smooth or winding leaf
lobes, arranged spirally
around the stem
Cassava roots are
conical, cylindrical or
irregular, and coloured
cream, yellow and light to
dark brown
42 Save and Grow: Cassava
CIAT has also supplied India’s Central Tuber Crops Research Institute
with tissue culture plants of lines with high levels of resistance to the
Indian and Sri Lankan cassava mosaic virus.
In four decades of work on cassava genetic improvement, IITA
has produced more than 400 improved varieties with traits such as
resistance to cassava mosaic disease (CMD), bacterial blight and green
spider mites. The varieties have been released throughout sub-Saharan
Africa, and are estimated to have doubled cassava yields in some
countries. IITA’s scientists identified three different sources of CMD
resistance – the wild “cassava tree” (Manihot glaziovii), found in Brazil,
and two Nigerian landraces. Some 40 varieties resistant to CMD have
been released in Nigeria, 36 in the United Republic of Tanzania, 30 in
the Democratic Republic of the Congo and 14 in Malawi. The disease
is now considered largely under control in areas where the resistant
varieties are planted.
Research at both CIAT and IITA has also focused on improving the
nutritional value of cassava by increasing its vitamin A, iron and zinc
content. Through breeding, scientists have been able to double the
content of carotenoids, a precursor of vitamin A, in cassava roots12.
Cassava biofortified with vitamin A has been released in several countries, including the Democratic Republic of the Congo and Nigeria.
The cassava genepool has already been extensively tapped to produce
income-generating technologies for farmers worldwide6. Great
scope exists for further improvements, as the rapid development of
molecular technologies deepens our understanding of the structure
and behaviour of the cassava genome, and the costs of sequencing and
molecular marker development decline.
With climate change threatening crop production in many parts
of the world, breeding efforts will focus increasingly on “stacking”
multiple traits in elite varieties. There should also be greater focus on
developing varieties for niche agro-ecologies and – since almost all
breeding is done in monoculture fields – for specific intercropping
systems, rather than for wide adaptation. That is because low-income
smallholders living in isolated areas with suboptimal soil conditions
need “smarter”, locally adapted varieties that can produce very good
yields with minimal use of agrochemicals or irrigation.
National programmes should be encouraged, therefore, to introduce the outputs of the pre-breeding activities of CIAT and IITA
into their own breeding programmes that use landraces and other
Chapter 3: Varieties and Planting Material 43
farmer-preferred genotypes as parents. Until now, the focus has been
on evaluating breeding lines from the CGIAR centres for wide adaptations; that work must now be complemented by introgressing traits
from locally adapted materials.
There are promising examples of cassava breeding for specific
industries and uses. Scientists at CIAT have identified a cassava mutation with root starch containing zero or near-zero amylose13, which
has extremely useful applications in industry14. That “waxy starch”
characteristic is now being incorporated into high-yielding commercial varieties by the Thai Tapioca Development Institute15. CIAT has
also identified an induced mutation that has starch granules one-third
the normal size, with a rough outer surface. The starch is expected
to be useful to the fuel-ethanol industry, as it requires less time and
energy to convert the starch into sugar, the first stage in fermentation
for ethanol production16.
Other on-going work at CIAT and partner organizations include
the routine application of molecular tools in cassava genetic improvement. For instance, a number of molecular markers for tracing the
inheritance of resistance to whiteflies, green mites and bacterial blight
are at varying stages of validation.
Molecular markers associated with a specific gene for resistance to
cassava mosaic disease are being used to select for resistance to this
devastating disease. High-yielding, locally adapted cassava varieties
resistant to CMD have been developed by CIAT as a precautionary
measure against the real possibility of the virus’s appearing on the
American continent. The use of molecular markers is also making
the trans-continental transfer of cassava germplasm possible. Latin
American cassava genotypes have been successfully introduced into
African cassava breeding programmes as the markers provided an
efficient means for deploying only those genotypes with resistance
to CMD.
Following the first demonstration of successful genetic transformation in cassava in 1996, a number of transgenic genotypes with
improved resistance to viruses and abiotic stress, reduced levels of
cyanogenic glycoside content, better nutritional qualities and modified
starch yield and characteristics have been developed17. Initially, the
capacity for developing cassava transgenes was restricted to a few
advanced laboratories in the United States of America and Europe.
However, cassava can now be genetically transformed in a number
44 Save and Grow: Cassava
of laboratories in Asia and Africa as well. The wide applicability of
this potentially useful means of producing “designer varieties” with
novel traits is enhanced by the continued development of genotypeindependent protocols for genetic transformation in cassava.
While there are a few cases of controlled trials of transgenic cassava
genotypes, none has been officially released anywhere in the world.
In addition to the technical challenges, intellectual property rights
and biosafety issues will need to be addressed before genetic transformation can become a method of choice for cassava improvement.
Recognizing those constraints, CIAT is investigating the production
of non-transgenic herbicide-resistant varieties that would reduce the
labour cost of weeding, which currently accounts for 20 to 40 percent
of production costs, and could greatly facilitate the adoption of
reduced-tillage practices6.
Farmer participation in variety trials and the choice of selection
criteria (known as participatory plant breeding, or PPB), needs to
become a key step in the development of new varieties. Farmers’
criteria must inform all stages of selection, and trials in farmers’ fields
should begin as early as possible in the selection process. National
programmes should incorporate PPB principles into the development
and deployment of improved cassava varieties, especially with the
increasing demand for niche cultivars suited to particular environments, cropping systems or end-uses. Agricultural extension services
in many countries will need to be substantially upgraded to ensure
that smallholder farmers reap the full benefits of improved cassava
varieties.
Planting material
T
he use of high quality planting materials that maintain genetic
purity and are free of diseases and pathogens is crucial in cassava
production. With vegetatively propagated crops, diseases and pests
can build up over several generations of propagation, a problem that
is negligible with botanic seeds. In addition, cassava stem cuttings
are perishable, bulky and cumbersome to transport, and require
considerable storage space. As cassava under subsistence agriculture
is typically harvested piecemeal over a period of one year or more,
storage of stakes until the next planting is logistically challenging.
Chapter 3: Varieties and Planting Material 45
As a result, many farmers do not save cassava stems for planting
and frequently source cuttings from neighbours or in local markets;
under such conditions, assuring the quality of planting material is
practically impossible.
Effective systems for routine multiplication and distribution of
disease-free planting material of improved varieties is essential for
sustainable intensification. Among major cassava producers, Thailand
has been the most successful in disseminating improved varieties
to its cassava farmers. In 1994, the Thai Government established a
special programme for the rapid multiplication and distribution of
new varieties with high yield potential, high harvest index, high root
starch content and early harvestability. The programme involved
the country’s Department of Agriculture and Kasetsart University’s
Faculty of Agriculture, which supplied the basic planting material,
and the Department of Agricultural Extension and the Thai Tapioca
Development Institute, which multiplied and distributed it. By 2000,
almost 90 percent of Thailand’s cassava area was planted to the recommended cultivars, compared to less than 10 percent a decade earlier7, 18.
Although several protocols have been developed for the rapid
multiplication of cassava, and could be scaled up for the dedicated production of material that meets quality standards19, very few countries
have a formal seed system for cassava multiplication. Efforts to involve
the private sector have made little progress, owing mainly to the plant’s
low multiplication rate, compared to that of cereals – while one cassava
stake can produce in a year enough stems for 10 new stakes, a maize
seed can yield 300 new seeds three months after planting.
Stakes cut from healthy
stems free of pests and
diseases have a higher
rate of sprouting and
produce higher root yields
46 Save and Grow: Cassava
In India, the indiscriminate use of infected planting material, the
non-availability of resistant varieties and the lack of commercial
interest in supplying healthy planting material have resulted in
the widespread incidence of cassava mosaic disease. The country’s
Central Tuber Crops Research Institute has developed procedures
for multiplying virus-free cassava meristems in vitro. However, no
private firms have adopted the technology in order to supply farmers
with virus-free cassava plants on a large scale, as they have done for
other high-value horticultural crops, such as banana and potatoes20.
To increase the efficiency of cassava stem production, IITA and
Nigeria’s National Root Crops Research Institute have developed
a rapid multiplication technology, which involves cutting cassava
stems into stakes with 2 or 3 nodes, rather than the usual 5 to 7. With
efficient field management, cassava stems can be harvested twice a
year, at 6 and 12 months after planting, yielding around 50 times more
stems than were used for planting21. A study in 2010 found that onethird of cassava farmers in Akwa Ibom State, Nigeria, were using the
technology to multiply stems of improved varieties, which they sold to
other farmers; their average earnings from sales were US$750 a year22.
In the absence of a national cassava seed system, cassava development programmes in a number of African countries have used a 3-tier
community-based system of rapid multiplication to supply farmers
with improved, healthy planting material23. At the top level, material
from breeders is multiplied under optimal agronomic conditions
on research stations and government farms to produce disease-free
foundation seed. The secondary level involves further multiplication
on 2 ha farms often run by farmer groups, community organizations
and NGOs. Certified material is then distributed to tertiary multiplication sites, which are the main and most readily accessible source of
stems24. In several countries, the approach includes the distribution
of “seed vouchers”, which allow low-income farmers to buy stems at
subsidized prices.
It is estimated that more than 300 000 households in western Kenya
and 80 percent of small-scale cassava farmers in Uganda are growing
improved varieties multiplied and distributed through the system23.
The African Technology Uptake and Up-scaling Support Initiative
(TUUSI) has called on the region’s policymakers to promote the 3-tier
approach more widely and to encourage the formal seed sector to
become involved in the certification, multiplication and distribution
Chapter 3: Varieties and Planting Material 47
of high quality planting material. TUUSI also recommends the
participation of NGOs and farmer associations as the best means of
ensuring that research outputs are adopted by the largest number of
cassava growers23.
A high level of grassroots participation in multiplication was
achieved by the Great Lakes Cassava Initiative, managed by Catholic
Relief Services and supported by the Bill & Melinda Gates Foundation.
Implemented in six countries of East and Central Africa, the initiative involved 10 agricultural research institutes, 53 local NGOs and
some 3 000 farmer groups. It established a network of 6 500 small
multiplication plots, averaging 0.3 ha, each serving around 350 local
farmers, and helped disseminate a total of 33.6 million stems. The
initiative also put in place a low-cost quality management protocol,
based on visual assessment, to evaluate varietal purity and score for
pests and diseases25.
The use of poor-quality planting material will remain one of the
major causes of low cassava yields, especially in Latin America and
Africa, for some time to come. In the absence of efficient systems
of multiplication and distribution, farmers can help to improve the
situation using some simple local practices:
 Cut stems from vigorous plants which are 8 to 12 months old,
show no symptoms of pests or diseases, are growing in fertile soil,
and produce high root yields. The long, straight primary stems of
late-branching varieties are the most suitable.
Store
cut stems in an upright position in the shade, with the base

of the stems resting on soil that has been loosened with a hoe and
is watered regularly. Stems that have been stored for no more than
5 days before being cut into stakes will sprout more quickly.
Cut
stems into stakes 20 cm long, each with 5 to 7 nodes, imme
diately prior to planting. The diameter of the stakes should be at
least 3 cm, while the diameter of the pith should be less than half
the diameter of the stem.
 Before planting, soak the stakes for 5 to 10 minutes in hot water
to kill pests or disease-causing organisms that might be present.
Getting the right water temperature is also simple – mix equal
amounts of boiling and cold water26.
To ensure high yields, the stakes’ mother plants should have been
adequately fertilized. Cassava plants grown in soil with low levels of
nitrogen, phosphorus and potassium produce stakes that are also low
48 Save and Grow: Cassava
in those nutrients, and are also low in starch, reducing sugars and
total sugars. In turn, plants grown from stakes with a lower nutrient
content have a lower rate of sprouting, produce fewer stems and have
lower root yields (Annex table 3.2)27.
Even within a uniformly fertilized field, some plants grow better
and produce more roots than others. Farmers can increase the size of
their next cassava harvest by cutting the stems to be used as planting
material only from plants with high root yields. This simple practice
will markedly increase production, especially when using traditional
varieties that may be susceptible to pests and diseases.
Chapter 4
Water
management
Once established, cassava can grow
in areas that receive just 400 mm
of average annual rainfall.
But much higher yields are obtained
with higher levels of water supply.
Chapter 4: Water Management 51
T
he sole source of water for around 80 percent of the world’s
farmland is rainfall. Rainfed crop production accounts for as
much as 60 percent of global agricultural output and is the
source of livelihoods and food security for millions of the
world’s poorest farmers. Irrigated agriculture, with its higher cropping
intensities and higher average yields, produces up to three times more
from the same unit area of land.
Both rainfed and irrigated agriculture face major challenges.
As competition for increasingly scarce water resources intensifies,
irrigation is under growing pressure to produce “more crops from
fewer drops” and to reduce its negative environmental impacts,
including soil salinization and nitrate contamination of drinking water.
Greater use of water-saving precision technologies, such as drip and
micro-irrigation, will make an important contribution to sustainable
intensification.
Climate change poses grave risks to rainfed agricultural production.
Scenarios indicate a decline of some 30 percent or more in runoff from
rainfall over large areas of sub-Saharan Africa, South Asia and Latin
America by 2050. As water flows become more variable and uncertain,
and the incidence of droughts and floods increases, crop yields are
projected to decline in many developing countries1.
Nevertheless, a comprehensive assessment of water management in
agriculture has found that the greatest potential for yield increases is
in rainfed areas2. But realizing that potential will require implementation of key “Save and Grow” recommendations: the use of improved,
drought-tolerant varieties, widespread adoption of conservation tillage,
mulching and other soil improvement practices, the reversal of land
degradation, and adding an irrigation component to rainfed cultivation
through rainwater harvesting and supplemental irrigation2.
Unlike most other food crops, cassava does not have a critical period
during which adequate soil moisture is essential for flowering and
seed production. It also has several defence mechanisms that help it
to conserve water, and its roots can grow to great depths to access
subsoil moisture reserves3. As a result, cassava can withstand relatively
prolonged periods of drought4.
However, the crop is very sensitive to soil water deficit during the
first three months after planting. Stakes will only sprout and grow well
when the temperature is above 15°C and the soil moisture content is
at least 30 percent of field capacity5. Water stress at any time in that
52 Save and Grow: Cassava
early period reduces significantly the growth of roots and shoots,
which impairs subsequent development of the storage roots, even if
the drought stress is alleviated later6, 7.
Once established, cassava can grow in very dry areas – such as
northeast Brazil – that receive just 400 mm of average annual rainfall3.
In southern India, the crop’s water requirement is put at from 400 to
750 mm for a 300-day production cycle. But higher yields have been
obtained with much higher levels of water supply. Research in Thailand
found that maximum root yields were correlated with rainfall totalling
about 1 700 mm during the 4th to 11th month after planting8.
Cassava also responds well to irrigation. In trials in Nigeria, root
yields increased sixfold when the quantity of water supplied by
supplementary drip irrigation matched that of the season’s rainfall9.
However, cassava is also susceptible to excess water – if the soil
becomes water-logged, sprouting and early growth is affected and
yields fall.
Rainfed production
I
n most parts of the world, cassava is almost exclusively a rainfed
crop. Optimizing rainfed cassava production requires, therefore,
careful attention to planting dates, the use of planting methods and
planting positions that make the most of available soil moisture, and
soil management practices that help to conserve water.
Cassava can be planted throughout the year if rainfall is evenly
distributed, but not during periods of heavy rains or drought10. In
areas with only one rainy season per year, farmers usually plant as
soon as the rains start – generally around April-May in the northern
tropics and October-November in the southern tropics. A survey in
Thailand in 1975 found that almost 50 percent of the cassava crop was
planted in the period April to June (Figure 13).
Once well-established, young plants will grow deeper roots as
the topsoil begins to dry out with the arrival of the dry season. In
Andhra Pradesh State, India, farmers plant cassava in well-watered
nursery beds, before the onset of the 5-month rainy season, in order
to induce sprouting and root development. When the rains start, the
rooted stakes are transplanted to the field. If the early rains do not
persist and some of the transplanted stakes die, they are replaced by
Chapter 4: Water Management 53
newly sprouted stakes from the nursery Figure 13 Rainfall and area of cassava planted
beds. Using this approach, farmers can each month in Thailand
make optimum use of the short wet season
300
Planted area (%)
without the need for irrigation.
20
Rainfall (mm)
In southern Nigeria, planting usually
250
takes place between March and April, at
200
the onset of the rainy season, although 15
later planting – in June, at the peak of the
150
rains, with harvesting 10 months later 10
during the long dry season – produces
100
higher profit margins11. Delaying planting
5
beyond June in southern Nigeria can lead to
50
drastic yield reductions, of up to 60 percent
0
0
(Figure 14)12.
Jan
Mar
May
Sep
Nov
Jul
In areas with two relatively short rainy
seasons per year, cassava can be planted Source: Adapted from Sinthuprama, S. 1980. Cassava planting systems in Asia. In E.J. Weber,
J.C. Toro and M. Graham (eds.). Cassava cultural practices.
in the early or middle part of either rainy Proc. of a Workshop, held in Salvador, Bahia, Brazil. March 18-21, 1980. pp. 50-53.
season and harvested after 10 to 14 months,
preferably during the dry season, when the root starch content is
highest. In Kerala State, India, cassava is usually planted in April-May,
with the start of the southwest monsoon, and in September-October,
when the northeast monsoon arrives. However, some farmers plant
short-duration cassava in lowland paddy fields in February, after the
Figure 14 Effect of planting
rice has been harvested, and the soil is still wet. The crop benefits from
the remaining soil moisture during the dry months that follow, and date on root yield of late
season cassava, Nigeria (%)
is harvested after eight months, before the land is used again for rice.
120
Planting early in the rainy season will generally produce the highest
yields because the plants have adequate soil moisture during the most
critical part of their growth cycle. However, research has shown that
yields can vary according to the variety used, the soil type, the plant’s
age at harvest, and the rainfall intensity and distribution during any
particular year.
In Thailand, planting in June produced average root yields of
almost 40 tonnes per ha, compared to 27 tonnes when planting was
in September, the month with the heaviest rainfall, and 22 tonnes in
October, the beginning of the dry season (Figure 15)10.
However, later research at the same location in Thailand, using
four improved Rayong varieties, showed that the highest average yield
was obtained by planting in August to November; planting either
100
80
60
40
20
0
Jun Jul Aug Sep Oct
Month of planting
Source: Annex Table 4.1
54 Save and Grow: Cassava
early, in April-May, or late, in December-March, produced much lower yields. A more recent experiment
conducted over three consecutive years produced a
45
different result again. The highest root yields were
40
obtained when cassava was planted in December, in
35
the early dry season, and harvested after 11 months,
30
in November (Figure 16)8.
The explanation: in the location used for the trials,
25
rain
falls occasionally during the dry season and
20
provides enough soil moisture to produce 90 percent
15
of the potential plant stand. Planting even later in the
10
dry season, in February, resulted in lower root yields
5
but higher starch content. By plotting root yield and
starch content against rainfall during specific periods
0
May
Jun
Jul
Aug
Sep
Oct
of the growth cycle, it was found that root yields were
* roots harvested at 8, 10, 12, 14, 16 and 18 months
best correlated with total rainfall during the 4th to
Source: Annex Table 4.2
11th month (March to October), while starch content
was best correlated to rainfall during the 6th to 9th month (July to
October), after planting8.
Figure 15 Effects of time of planting on
average cassava root yield*, Thailand (t/ha)
Figure 16 Effect of different planting dates and average rainfall
on cassava root and starch yield, Thailand (t/ha)
mm Total rainfall
in 11-month period
Root yield
Starch yield
1402 mm
1409 mm
1267 mm
1665 mm
Jun
Aug
Oct
Dec
1633 mm
1616 mm
30
25
20
15
10
5
0
Feb
Month of planting with harvest after 11 months
Source: Annex Table 4.3
Apr
Chapter 4: Water Management 55
Planting methods need to be tailored to soil moisture conditions
under rainfed production. When the soil is not well drained and too
wet owing to heavy rains, it is better to plant stakes on the top of
ridges or mounds to keep the roots above the standing water. That
will also reduce root rots. However, where cassava is planted during
dry periods in Thailand, the rates of stake sprouting and plant survival
are significantly higher when cassava stakes are planted on the flat,
owing mainly to the slightly higher soil moisture content in the top
30 cm of soil (Figure 17)13.
Similarly, stakes should be planted at a shallow depth, of 5 to 10 cm,
in heavy and wet soils, but slightly deeper in light-textured and dry
soils to avoid surface heat and lack of moisture. In Thailand, planting
stakes vertically or inclined at a 45 degree angle produced significantly higher yields and root starch contents than horizontal planting
(Figure 18). The yield gap was even more pronounced when the stakes
were planted early in the dry season and at shallow depths, because of
hot, dry conditions close to the soil surface. With horizontal planting,
sprouting was markedly delayed and the plant stand was reduced13.
If the first rains are intense, the risk of waterlogging is greatest in
shallow soils, and also in poorly drained soils where the subsoil has
been compacted by heavy machinery. The risk of waterlogging can be
reduced with zero tillage, which
Figure 18 Effect of stake planting
improves internal drainage (see
position on cassava root yield in
rainy and dry season, Thailand (t/ha) Chapter 2, Farming systems).
Where tillage is practised, soil
should be prepared when it is
Horizontal
Vertical
20
not too dry or too wet – which
Inclined
18
reduces the number of plough16
ing and harrowing passes re14
quired – and, if necessary, a
12
subsoiler can be used to break
10
up the compacted layer.
8
Sometimes, it may be better
6
to delay planting to the latter
4
part of the rainy season, but no
later than about two months
2
before the onset of the dry sea0
Rainy season Early dry season
son. Planting towards the end,
(May-August)
(November)
rather than at the beginning, of
Source: Annex Table 4.4
the rainy season usually results
Figure 17 Effect of planting
method on cassava plant
survival in rainy and dry
season, Thailand (‘000/ha)
Ridge
planting
Flat
planting
14
12
10
8
6
4
2
0
Rainy
season
(MayAugust)
Source: Annex Table 4.4
Early dry
season
(November)
56 Save and Grow: Cassava
in lower yields, but it has some advantages: less weed competition
and – if the crop is harvested in the off-season – the possibility of
higher market prices. Another advantage is that the late planting of
cassava does not coincide with other major agricultural activities, so
there is less competition for labour.
Irrigated production
W
hen it is planted towards the end of the rainy season, or
when the rainy season is very short, cassava benefits from
supplemental irrigation during rainless periods. On land that is flat,
or nearly flat, this can be done by flood or furrow irrigation, but on
sloping land it may be more practical to use overhead sprinklers or a
rotating water cannon.
Research in India found that during periods of drought, yields
increased with increasing amounts of surface irrigation water applied.
Full irrigation, at 100 percent of crop water requirements, doubled the
root yield obtained without irrigation. It also increased slightly the
Figure 19 Effect of
supplemental irrigation*
on cassava root yield,
India (t/ha)
45
Figure 20 Effect of supplemental drip irrigation on cassava root yield,
Nigeria (t/ha)
25
40
35
20
30
25
15
20
15
10
10
5
0
5
Rainfed
Full
irrigation
* during drought periods
(more than 7 days without rain)
Source: Annex Table 4.5
0
Zero
20 percent
50 percent
Irrigation water applied as percentage of effective rainfall
Source: Annex Table 4.7
100 percent
Chapter 4: Water Management 57
starch content of roots and markedly reduced the hydrogen cyanide
content (Figure 19)14.
More effective, in terms of water use efficiency, is drip irrigation
which, by providing small and frequent water applications, saves water
while maintaining soil moisture at a level that is highly favourable to
crop growth (it also allows the farmer to water the cassava plants but
not the weeds). In trials in the very dry zone of Tamil Nadu, India,
drip irrigation of cassava produced about the same yields as those
obtained with flood irrigation – around 60 tonnes per ha – using
50 percent less water. When the water applied through drip irrigation
was equal to that used in flood irrigation, yields continued to increase
substantially, to 67.3 tonnes (Annex table 4.6)15.
Similar results were reported from experiments in south-western
Nigeria. With 730 mm of effective rainfall during the growing season,
rainfed cassava produced root yields of less than 5 tonnes per ha. In
plots under supplemental drip irrigation, yields rose sharply with
increasing levels of water applied. At 100 percent of rainfall, drip
irrigation produced yields of 28.1 tonnes, equal to total water use
efficiency of 18.8 kg per ha per mm, compared to 6.2 kg without
irrigation (Figure 20). Yield increases at lower application rates were
also significant – supplemental irrigation that boosted the total water
supply by 20 percent almost doubled root yields9.
With drip irrigation,
researchers in Nigeria
increased root yields from
4.6 to 28 tonnes
Chapter 5
Crop nutrition
Combining ecosystem processes
and judicious use of mineral fertilizer
forms the basis of a sustainable crop
nutrition system that produces more
while using fewer external inputs.
Chapter 5: Crop Nutrition 61
T
o achieve the higher productivity needed to meet current
and future demand, agriculture must, literally, return to
its roots by rediscovering the importance of healthy soil,
drawing on natural sources of crop nutrition and using
mineral fertilizer wisely.
The over-use of mineral fertilizer in agricultural production has
carried significant costs to the environment, including the acidification
of soil, the contamination of water, and increased emissions of potent
greenhouse gases. More targeted and sparing use of fertilizer would
save farmers money and help to ensure that nutrients reach crops and
do not pollute air, soil and waterways.
The impact of mineral fertilizer on the environment is a question of
management: how much is applied compared to the amount exported
with crops, and the method and timing of applications. In other
words, it is the efficiency of fertilizer use, especially of nitrogen (N)
and phosphorus (P), which determines if this aspect of soil fertility
management is a boon for crops or a negative for the environment.
Experience indicates that higher and more sustainable yields are
achieved when crop nutrients come from a mix of mineral fertilizer
and organic sources, such as animal manure and trees and shrubs
which, in dryer climates, can pump up from the subsoil nutrients that
would otherwise never reach crops. Crop nutrition can be enhanced by
other biological associations – for example, between plant roots and
soil mycorrhizae. In “Save and Grow”, that combination of ecosystem
processes and judicious use of mineral fertilizer forms the basis of a
sustainable crop nutrition system that produces more while using
fewer external inputs1.
Cassava can grow and produce reasonable yields on soils where
many other crops would fail. It is highly tolerant of soils with low levels
of phosphorus and can generally grow even with no application of
P-fertilizer. That is because cassava has formed a mutually beneficial
association with a group of soil fungi called “vesicular-arbuscular
mycorrhizae”2, 3. Present in practically all natural soils, mycorrhizae
penetrate the cassava root and feed on the sugars it produces. In
exchange, the fungi’s long filaments transport phosphorus and
micronutrients to the root from a greater volume of the surrounding
soil than the root alone could reach. That symbiotic association allows
cassava to absorb sufficient phosphorus for healthy growth.
62 Save and Grow: Cassava
Most of the nutrients absorbed by cassava during growth are found
in the plant tops4. Returning stems and leaves to the soil – both as leaf
litter and as mulch after the root harvest – enriches the soil with new
organic matter, and some of the nutrients are re-used by the next crop
(Figure 21). In fact, when the plant tops are recycled, fewer soil nutrients are exported in the root harvest than in the harvest of most other
crops5, 6 – a root yield of 15 tonnes per ha removes only about 30 kg
of nitrogen, 20 kg of potassium (K) and just 3.5 kg of phosphorus7-9.
There is little danger of phosphorus depletion, therefore, even after
many years of continuous cassava
Figure 21 Distribution of nutrients in 12-month-old
production on the same land10.
unfertilized cassava, Colombia (%)
Cassava can also be grown on very
100
acid
and low-fertility soils because it
90
tolerates low pH and the associated
80
high levels of exchangeable alumin70
ium. While the yields of crops such
60
as maize and rice are usually affected
50
strongly when the soil pH is below 5
40
and aluminium saturation is above
30
50 percent, cassava yields are normally
20
not affected until the soil pH is below
10
4.2 and aluminium saturation is above
0
80 percent. For that reason, cassava
N
P
K Ca Mg S
B Cu Fe Mn Zn
may not require large amounts of lime
in acid soils, where other crops would
Tops and fallen leaves
Roots
not grow without them.
Source: Annex Table 5.1
Mineral fertilizer
I
ts ability to produce on low-fertility soils has given rise to the misconception that cassava does not require, nor even respond to, the
application of mineral fertilizer. In fact, the results of extensive trials
reviewed by FAO have shown that many cassava varieties respond
very well to fertilization11. If anything, cassava’s need for fertilizer is
increasing as traditional means of maintaining soil fertility – such as
intercropping and the mulching of plant residues – are abandoned
under more intensive production systems.
Chapter 5: Crop Nutrition 63
When root yields are high, and residues are not returned to the
soil, the harvest removes large amounts of nitrogen and potassium.
To sustain both yields and soil fertility, cassava would require annual
per hectare applications estimated at 50 to 100 kg of nitrogen, 65 to
80 kg of potassium and 10 to 20 kg of phosphorus, depending on the
soil’s native fertility and the desired yield levels.
Results from 19 long-term fertility trials, conducted over 4 to
36 years of continuous cassava cropping on the same plots, indicate
that the main nutrient constraint was lack of K in 12 trials, of N in five
trials and of P in only two trials. In Thailand, high root yields of up to
40 tonnes per ha were maintained when adequate amounts of mineral
fertilizer (100 kg N + 22 kg P + 83 kg K) were applied annually and
plant foliage was returned to the soil before each new planting. When
no fertilizer was applied and plant tops were removed from the field,
per hectare yields declined sharply, from 30 tonnes in the first year to
about 7 tonnes after six years, owing to nutrient depletion, especially
of potassium (Figure 22). Similar results have been witnessed on a
wide range of different soils in Colombia, India, Indonesia, Malaysia,
Thailand and Viet Nam9.
Cassava yields in Africa could be increased markedly if farmers had
access to mineral fertilizer at a reasonable price. In the Democratic
Republic of the Congo, the use of improved, pest- and disease-resistant
varieties, in combination with appropriate rates of mineral fertilizer,
Figure 22 Effect of mineral fertilizer and crop residue management on cassava root yields
over 25 crop cycles, Thailand (t/ha)
50
Fertilizer+tops recycled
45
No fertilizer, no tops recycled
No fertilizer+tops recycled
40
35
30
25
20
15
10
5
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Cassava crop cycles
15
16
17
18
19
20
21
22
23
24
Source: Howeler, R.H. 2012. Effect of cassava production on soil fertility and the long-term fertilizer requirements to maintain high yields.
In R.H. Howeler, ed. The cassava handbook – A reference manual based on the Asian regional cassava training course, held in Thailand. Cali, Colombia, CIAT. pp. 411-428.
25
64 Save and Grow: Cassava
led to increases in cassava root yields – of 30 to 160 percent – as well
as in stem yields, important for production of high quality planting material. In the west of the country, per hectare cassava yields
increased from 12 to 25 tonnes with moderate applications of N-P-K
fertilizer, and reached more than 40 tonnes with higher application
rates12. (However, fertilizer costs in sub-Saharan Africa remain high.
Where using fertilizer on cassava is not economical, the crop may
benefit from the residues of fertilizer applied to other crops of higher
economic value, such as maize and soybean13.)
Initially, cassava should be fertilized with equal amounts of N,
phosphorus pentoxide (P2O5) and potassium oxide (K2O) at a rate of
500 kg to 800 kg per ha of a compound fertilizer such as 15-15-15 or
16-16-16. However, if the crop is grown continuously for many years
on the same land, the N-P-K balance will need to be modified to
compensate for the corresponding removal of each nutrient in the root
harvest. That can be done by using fertilizers with a ratio of N, P2O5
and K2O of about 2:1:3, such as 15-7-20, or any compound fertilizer that
is high in K and N, and relatively low in P. Farmers should follow local
fertilizer recommendations based on experimental results obtained
with the crop or on the results of simple fertilizer trials conducted in
their own fields with the help of an agronomist or extension worker.
Soluble fertilizers – such as urea, single- and triple-superphosphate,
di-ammonium phosphate, potassium chloride and potassium sulphate
– and most compound fertilizers should be applied either when the
stakes are planted or, preferably, about one month later, when the
roots have emerged. Phosphorus should be applied at or shortly after
planting. N and K are best applied in split doses, one half at or shortly
after planting, and the rest at 2 to 3 months after planting, when
cassava reaches its maximum growth rate.
Most mineral fertilizers dissolve rather rapidly in soil water. They
should be applied in short bands, dug with a hoe, 20-30 cm long and
4-5 cm deep at a distance of about 5-10 cm from the cassava stake or
plant. After application, the fertilizers should be covered with soil to
prevent volatilization of N and losses of nutrients through runoff and
erosion. The roots of the plant will grow towards the fertilizer band in
order to take up the nutrients dissolved in the soil solution. Localized
application helps to avoid fertilizing weeds that may grow nearby.
Chapter 5: Crop Nutrition 65
Figure 23 Effect of four sources of nitrogen on cassava root yield,
India (t/ha)
30
25
20
15
10
5
0
Urea
Neem-coated
urea
Urea
super granules
Rubber
cake-coated
urea
Source: Annex Table 5.2
To reduce economically wasteful and environmentally harmful
losses of fertilizer nutrients, “Save and Grow” farming systems seek
to maximize fertilizer use efficiency. Trials in India have shown
how the supply of nitrogen fertilizer to cassava can be optimized by
using urea compressed into supergranules or urea prills coated with
cake made from neem seed oil (Figure 23)14. Both technologies slow
considerably the nitrification of the urea, reducing losses to the air
and to surface water runoff, and ensuring a continuous supply of
nitrogen to match the requirements of the crop at different stages of
growth. In trials, the neem-coated urea produced average root yield
increases of 27 percent15.
Less soluble fertilizers, such as rock phosphate, lime, gypsum,
sulphur and organic compost and manure, are usually broadcast over
the entire field and incorporated before planting, in order to achieve
good contact with the soil and enhance the rate at which they dissolve
or decompose. In reduced or zero tillage systems, they should be
applied at the bottom of the planting holes at the time of planting.
66 Save and Grow: Cassava
Organic sources of nutrients
W
hile mineral fertilizer can help to boost yields, alone it cannot
sustain crop production in the long-term on degraded land16.
Farmers need to maintain and improve soil quality and health using
a number of other “Save and Grow” measures, such as conservation
tillage, intercropping, green manuring, mulching crop residues and
cover crops, alley cropping, and applying animal manure or compost
(see also Chapter 2, Farming systems).
Fast-growing groundnuts
protect soil from erosion
and provide cassava with
a source of nitrogen
In Viet Nam, alley
cropping with the
leguminous tree
Leucaena leucocephala
(at right) increased
yields – but it may not be
as effective in the humid
tropics
Intercropping with grain legumes, which fix atmospheric nitrogen,
make some N available to the cassava crop. Although biological fixation cannot meet all of cassava’s nitrogen needs, it has some benefits. In
Nigeria, after two years of cassava-soybean intercropping, incorporation of soybean residues led to yield increases of 10 to 23 percent17.
Research at two locations in the Democratic Republic of the Congo
found that planting four rows of groundnuts between widely spaced
rows of cassava also boosted root yields. But higher yields still were
obtained in both locations with the application of 17-17-17 compound
fertilizer at the rate of 150 kg per ha, divided evenly between the
cassava and the intercrop.
The fertilizer treatment
produced the highest net
benefits in one location
during the first year, while
intercropping with groundnuts and without fertilizer
produced the highest net
benefit in the second year.
Despite its high price in the
region, mineral fertilizer
was the treatment most
preferred by farmers19.
Alley cropping with deeprooting and fast-growing
leguminous trees may be an
effective means of improving soil fertility and yields,
where mineral fertilizer is
Chapter 5: Crop Nutrition 67
not available. In a long-term soil improve- Figure 24 Effect of alley crops on cassava root yield,
ment experiment in southern Viet  Nam, alley Viet Nam (t/ha)
cropping with two leguminous tree species, 25
fertilized
unfertilized
Leucaena leucocephala and Gliricidia sepium,
had a marked and consistent long-term benefi- 20
cial effect on cassava grown in alleys 4 m wide,
both when cassava was fertilized and when 15
it was not fertilized. During the 16th year of
continuous cropping on the same plots, fertil- 10
izer application alone boosted root yields from
4.8 tonnes to 17.4 tonnes per ha, while alley 5
cropping with Leucaena and without fertilizer
increased yields to 13.4 tonnes. Combining
Leucaena with fertilizer achieved yields of more 0
Monoculture
Cassava+
Cassava+
than 20 tonnes (Figure 24).
Leucaena
Gliricidia
However, the benefit of alley cropping is lim- Source: Annex Table 5.3
ited in the humid tropics, which are dominated
by large areas of low-fertility ferralsols. The alley cropping of trees in
such areas does not automatically lead to higher cassava yields – a
review of experiments in the humid zone of West and Central Africa
revealed that, in the majority of trials, it had either no effect or a
negative effect on cassava root growth19. Those results were probably
due to the fact that, in more humid climates, the tree roots tend to
remain in the upper levels of the soil, where they compete strongly
with cassava.
Green manuring – the practice of growing a grain- or forage legume
for some months, then mulching the residues prior to planting the
cassava crop – also improves soil fertility, especially levels of nitrogen.
Combinations of cassava with legumes have a definite biological
advantage over monocropping because the area by time occupancy of
the land is higher. That biological advantage decreases, however, with
the duration of the legume crop, which should not exceed 90 days20.
Many green manure species have been tested, both in Colombia and
Thailand, to measure their effect on cassava21. Green manures used
in Colombia include native weeds, cowpeas, groundnuts, pigeon peas,
velvet beans (Mucuna pruriens), jack-beans (Canavalia ensiformis), the
perennial forage legume Zornia latifolia and tropical kudzu (Pueraria
phaseoloides). The grain legumes were harvested after four months
and the forages were cut after six months, before being incorporated
68 Save and Grow: Cassava
Tithonia diversifolia, a
wild sunflower found
throughout the tropics,
makes nutrient-rich,
high-quality mulch
into the soil. Cassava was planted one month afterward, in plots with
and without mineral fertilizer.
Although root production increased most markedly with the application of fertilizer, incorporation of green manures helped to boost
yields when no fertilizer was applied. Groundnuts were among the
most beneficial green manure crops, but Zornia latifolia and kudzu
were also very effective, especially in the presence of fertilizers.
On very sandy soils in Colombia, the mulching of native weeds –
tall grasses and creeping legumes – proved to be the best method of
fertilization, in the absence of mineral fertilizer. The application of 3
to 4 tonnes of dry mulch per ha led to yield increases similar to those
produced by the application of 500 kg of 15-15-15 mineral fertilizer21, 22.
Trials conducted in Thailand showed that several green manures,
especially sunn hemp (Crotalaria juncea), also increased cassava
yields21.
Another approach is to plant the green manure at the same time
as the cassava, but in between the cassava rows, similar to an intercrop. The fast-growing green manures are pulled out 2 or 3 months
after planting, and mulched between the rows. The manure crops
Canavalia ensiformis and Crotalaria juncea have proven particularly
effective in increasing cassava root yields.
Material for organic soil cover can also be collected off-site. Some
species, such as Tithonia diversifolia, a wild sunflower found growing
along roadsides throughout the tropics, make high-quality mulch.
Tithonia is particularly high in N and K, although its nutrient content
varies according to where it grows. In East Africa, the usual practice
is to cut and chop leaves and soft twigs into small pieces, before the
plant flowers, and spread them evenly over the soil surface23.
At two sites in the Democratic Republic of the Congo, Kiduma and
Mbuela, incorporating into the soil 2.5 tonnes per ha of dry matter of
Tithonia diversifolia and Chromolaena odorata before cassava was
planted produced very marked increases in yields, similar to those
obtained with the application of low to moderate levels of N-P-K
compound fertilizers24. When they were applied in combination
with low or moderate levels of fertilizer, cassava yields increased even
beyond those obtained with higher fertilizer rates.
Tithonia was more effective in increasing cassava yields than
Chromolaena in Kiduma, but not in Mbuela, owing to the much lower
nutrient content of Tithonia collected at the latter site. Application of
mineral fertilizer at low, moderate and high levels increased cassava
Chapter 5: Crop Nutrition 69
yields significantly at both sites, and fertilizer Figure 25 Effect of mineral fertilizer and green manure
residues remaining in the soil benefited the on cassava root yield at two sites in DR Congo (t/ha)
following cassava crop (Figure 25).
45
Kiduma
Despite the high cost of fertilizer, the 40
net economic benefits increased with ferMbuela
tilizer application, up to the highest rate 35
in Kiduma and up to a moderate rate in 30
Mbuela. However, the cost-benefit ratio 25
and marginal rate of return were highest for 20
Tithonia. In areas where mineral fertilizer 15
is not available or is too costly, therefore,
10
cassava yields can be markedly improved
by incorporating locally available vegetation, 5
0
such as Tithonia or Chromolaena.
No treatment
Fertilizer
Fertilizer
However, they may not always be avail(1 417 kg/ha)
(850 kg/ha)
able, and are cumbersome to collect and
+Tithonia
transport at the high rates of application Source: Annex Table 5.4
used in the Congolese experiments. In addition, Tithonia can easily become a weed in the field where it has
been applied as green manure, and Chromolaena odorata is a favoured
breeding site of the African grasshopper Zonocerus variegatus, a major
pest of cassava in West Africa.
So, while green manure can definitely play an important role in
maintaining soil fertility and improving cassava yields, the practice and
the green manure species selected need to be adapted to the conditions
of the growing area. Since cassava has a long growth cycle, farmers
may be reluctant to use part of that year for green manure production.
In many cases, they will prefer to invest in mineral fertilizer.
Animal manure and compost are used by smallholder farmers around
the world to increase crop production. Among the various types,
chicken manure tends to have the highest nutrient content. Manure
and compost are both good sources of organic matter which, when
incorporated into the soil, improve its structure and aggregate stability,
and enhance water holding and cation exchange capacity. They also
facilitate the below-ground biological activity of earthworms, bacteria
and fungi, and supply a wide range of nutrients, including secondary
and micro-nutrients.
An IITA-led research programme on agricultural development
in the humid tropics is investigating the potential benefits to soil
70 Save and Grow: Cassava
fertility of livestock integration with cassava production.
Livestock integration will add
value to green manure species
and cassava leaves when they are
used as feed, which in turn will
increase returns of animal manure to fields and crop yields16.
Trials indicate that combining
about 3 to 5 tonnes of manure
or compost per ha with mineral
fertilizer that contains the right
balance of N, P and K is often the
most effective means of increasManure
Compost Nitrogen Nitrogen
(10 t/ha)
(10 t/ha) (135 kg/ha) (135 kg/ha) ing yields and maintaining the
+manure +compost soil’s productive capacity. The
(5 t/ha)
(5 t/ha)
fertilizers supply the bulk of the
macro-nutrients needed by the
plants, while the organic sources provide secondary and micronutrients – which are only needed in very small quantities – and
improve the soil’s physical condition.
In trials in Indonesia and Viet Nam, a combination of compost or
farmyard manure – five tonnes per ha in both cases – with judicious
selection and use of mineral fertilizers – nitrogen and potassium in
Viet Nam (Annex table 5.5), and only nitrogen in Indonesia (Figure
26) – produced high crop yields and the highest net income.
The main drawback to organic sources of nutrients is that they
contain relatively low levels of nitrogen, phosphorus and potassium – it
takes one tonne of animal manure or compost to supply the same
amount of the major nutrients as 50 kg of a compound fertilizer
(Annex table 5.7). For small-scale farmers in isolated rural areas,
the lack of roads, transport and on-farm machinery may make the
collection and application of several tonnes of manure or compost
cumbersome and expensive, if not impossible.
Figure 26 Effect of mineral and organic fertilizers on cassava fresh
root yield, Indonesia (t/ha)
45
40
35
30
25
20
15
10
5
0
No
Nitrogen
treatment (135 kg/ha)
Source: Annex Table 5.6
Chapter 5: Crop Nutrition 71
Controlling soil erosion
B
ecause the topmost soil layer is the most fertile, control of soil
erosion is essential for sustainable soil fertility management.
Removal of topsoil causes the loss not only of available or exchangeable nutrients, but the total amounts of nutrients in the organic and
mineral fraction25.
Growing cassava tends to cause more soil losses to erosion than
growing most other crops, especially where farmers do not use cover
crops or mulches to protect the
Figure 27 Effect of soil conservation practices on cassava root
soil from the direct impact of rain, yield and dry soil loss due to erosion, Viet Nam (%)
sun and wind during the first 2 to 160
3 months of growth10. In addition,
Relative cassava yield
Relative dry soil loss
cassava is often grown on sandy or 140
sandy-loam soils that have low ag- 120
gregate stability, and on slopes that 100
are already eroded, partly because
cassava is one of few crops that can 80
produce reasonably well on exposed 60
subsoils.
40
“Save and Grow” practices can
reduce runoff and erosion signifi- 20
cantly, while helping to increase 0
No
Fertilizer
Fertilizer
Fertilizer
cassava yields. One option is minifertilizer or
+closer
only
+paspalum
mum or zero tillage (see Chapter 2,
hedgerows
spacing
hedgerows
Farming systems), which protects Source: Annex Table 5.8
the soil from erosion, slows the
decomposition of organic matter and maintains soil aggregate stability
and internal drainage. A study in Colombia found that a combination
of minimum tillage and grass-legume mixtures in rotation enhanced
microbial soil activity, which resulted in significant binding of soil
particles, thereby increasing aggregation and reducing soil erosion26.
Zero tillage is most effective in a well-aggregated soil with an adequate
level of organic matter.
If the land is prepared using conventional tillage, ploughing and
ridging on slopes needs to be done along the contour, rather than upand-down the slope, and contours should be planted with hedgerows
of grasses or shrub- or tree-legumes in order to slow runoff and trap
eroded sediments. Cassava stakes should be planted through mulch
(such as crop residues, grasses or leguminous tree prunings), and
intercrops should be grown as a soil cover between the cassava rows.
72 Save and Grow: Cassava
Studies in Colombia and in several Asian countries have shown that
among the practices most effective in controlling erosion are: planting
contour hedgerows of vetiver grass, Tephrosia candida or Paspalum
atratum; planting cassava on contour ridges; and planting Leucaena
leucocephala or Gliricidia sepium along the contour in alley cropping
systems (Figure 27). The benefit of all of those measures is enhanced
by applying mineral fertilizer to the cassava, because it leads to faster
soil coverage by the plant canopy.
Most erosion control practices have advantages and disadvantages,
and trade-offs need to be made. It is important to involve farmers
directly in testing and selecting the practices most suited to their soil
and climate, their socio-economic conditions and their traditions.
Chapter 6
Pests and diseases
Protecting cassava with pesticide
is usually ineffective and hardly ever
economic. A range of non-chemical
measures can help farmers reduce losses
while protecting the agro-ecosystem.
Chapter 6: Pests and Diseases 75
T
he first line of defence against crop pests and diseases is
a healthy agro-ecosystem. Because synthetic insecticide,
fungicide and herbicide disrupt the natural crop ecosystem
balance, “Save and Grow” seeks to minimize their use to the
extent possible. It promotes instead integrated pest management (or
IPM), a crop protection strategy that aims at enhancing the biological
processes and crop-associated biodiversity that underpin production1.
Crop losses to insects are kept to an acceptable minimum by
deploying resistant varieties, conserving and encouraging biological
control agents, and managing crop nutrient levels to reduce insect
reproduction. Diseases are controlled through the use of clean planting
material, crop rotations to suppress pathogens, and elimination of
infected host plants. Effective weed management entails timely manual
weeding and the use of surface mulches to suppress weed growth.
When necessary, low-risk selective pesticides may be used for
targeted control, in the right quantity and at the right time. Since all
pesticides are potentially toxic to people and the environment, the
products employed must be locally registered and approved, and carry
clear instructions on their safe handling and use.
Like all major crops, cassava is vulnerable to pests and diseases that
can cause heavy yield losses. Their impact is most serious in Africa.
Until recently, Asia had few serious pest and disease problems, but
this may be changing as the crop is grown more intensively over larger
areas and planted throughout the year for industrial processing.
When pest or disease management measures become necessary,
a strategy of non-chemical control should be considered before any
decision is taken to use pesticide. Since cassava is a long-season crop,
and exposed to pests and diseases for an extended period, pesticide is
usually ineffective and hardly ever economic. That is why insecticide,
for example, should be used only in short-term, localized applications
in “hot spots” where the pest is first observed, and only when the pest
is in its early stage of development.
A range of non-chemical measures can help farmers reduce losses
to pests and diseases while protecting the agro-ecosystem2-7. First,
planting material should be of varieties with tolerance or resistance
to the most important cassava diseases and pests, and taken from
mother plants that are free of disease symptoms and signs of pest attacks. As an extra precaution, stakes can be soaked in hot water to kill
pests or disease-causing organisms that might be present. In extreme
76 Save and Grow: Cassava
cases, soaking stakes in a solution of fungicide and insecticide may be
necessary. However, farmers who do so must have received training
in the correct use of pesticide and, in selecting chemicals, should
follow the recommendations of local plant protection specialists.
Ecosystem-based practices, such as mulching, planting hedges and
intercropping, can provide refuges for natural enemies of insect pests.
Building up soil organic matter increases pest-regulating populations
early in the cropping cycle.
During crop growth, applying adequate amounts of mineral fertilizer or manure to the crop can enhance its resistance or tolerance.
Insecticide should not be applied to the leaves of the growing cassava
plant, as it may kill natural biological control agents that help to
keep some major pests and diseases under control. For example,
insecticide kills cassava mites’ natural enemies – phytoseiid mite
predators – before killing the mites themselves. When natural predators are eliminated, the result is an increase in the pest population, to
which farmers may respond with increased use of pesticide, thereby
perpetuating and worsening the cycle of pest damage. Biopesticides,
such as extract of neem seed oil, are recommended for controlling
whiteflies, mealybugs and variegated grasshoppers. Whitefly and
mealybug numbers can also be reduced with sticky traps and by
spraying plants with soapy water.
Control of major cassava diseases
A
lthough the largest number of cassava diseases is found in Latin
America and the Caribbean, the plant’s centre of origin, many
of them are now also found in sub-Saharan Africa and Asia. Some
have evolved separately in Africa and Asia, and have not yet arrived
in the Americas.
Bacterial blight is one of the most widespread and serious of the
cassava diseases. Caused by the proteobacterium Xanthomonas
axonopodis pv. manihotis, it is transmitted mainly by infected planting
material or infected farm tools. It can also be spread from one plant to
another by rain splash, and by the movement of people, machines or
animals from infected fields to healthy fields. The bacterium infects
first the leaves, which turn brown in large patches and eventually
Chapter 6: Pests and Diseases 77
die, then the vascular tissues of the petioles and
woody stems.
The effect of bacterial blight on yields varies
according to factors such as location, variety,
weather patterns, planting time and the quality
of planting material. In 1974, the disease caused
losses of 50 percent in large plantations in Brazil.
Bacterial blight can also threaten food security by
reducing the production of cassava leaves, which
are an important source of vegetable protein in
Central Africa.
Although potentially devastating, bacterial blight
can be controlled effectively with “Save and Grow”
practices. They include:
 Use varieties with good tolerance (many tolerant,
high-yielding varieties are now available)
 Use healthy planting material from disease-free plants or plants
derived from meristem culture, rooted buds or shoots
 Before planting, treat stakes by soaking them in hot water at 50°C
for about 50 minutes. In extreme cases, and on the advice of local
plant protection specialists, stakes may be soaked for 10 minutes
in a solution of cupric fungicides
 Plant at the end of rainy periods
 After using tools in blight-infected plots, sterilize them in hot water
or in a dilute solution of a disinfectant, such as sodium hypochlorite
 Ensure that the plants are adequately fertilized, especially with
potassium
 Uproot and burn any diseased plants and infected crop residues
 Intercrop cassava with other species to reduce plant-to-plant dissemination of bacterial blight caused by rain-splash (fast growing
crops such as maize will also reduce dissemination by wind)
 To prevent the carry-over of the disease in the soil, rotate cassava
with other crops, or leave the field in fallow for at least six months
between cassava crops.
Viral diseases are usually transmitted through the use of infected
planting material. In addition, whiteflies – mainly of the species
Bemisia tabaci – are vectors for viruses that cause cassava mosaic
disease (CMD) and cassava brown streak disease (CBSD).
Misshapen leaves, lack
of chlorophyll, mottling
and wilting: symptoms of
cassava mosaic disease
78 Save and Grow: Cassava
Cassava mosaic disease is endemic in sub-Saharan Africa. Common
symptoms include misshapen leaves, chlorosis, mottling and mosaic.
Plants suffer stunting and general decline, and the more severe the
symptoms, the lower the root yield. In the mid-1990s, an unusually
severe form of CMD caused yield losses of 80 to 100 percent in parts
of Kenya and Uganda. CMD is also the most serious cassava disease in
India and Sri Lanka, where it can lead to root losses of up to 90 percent
in traditional varieties8.
Cassava brown streak disease causes corky necrosis in roots that
renders them unfit for consumption. The disease has been responsible
for total crop failures in parts of Africa’s Great Lakes region. In 2011,
FAO warned that none of the cassava varieties grown by farmers in
the region seemed to be resistant to CBSD. Even plants produced
from clean planting material can become infected through the
transmission of the virus by B. tabaci whiteflies from infected plants
in neighbouring plots. Because the symptoms of CBSD may not be
evident on the cassava leaves or stems, farmers may not be aware
that their crops are infected until they harvest the roots. The lack of
above-ground symptoms makes the use of disease-infected planting
material more likely.
Two key recommendations for control of both CMD and CBSD
are strict enforcement of quarantine procedures during international
exchange of cassava germplasm, and cultural practices, especially the
use of resistant or tolerant cultivars and virus-free planting material.
A major effort has been made to produce and distribute CMD- and
CBSD-free planting material in the Great Lakes region. January 2012
saw the release in the United Republic of Tanzania of four highyielding cassava varieties, bred through marker-assisted selection,
that are resistant to CMD and tolerant to CBSD.
A decade of intensive research at Kerala’s Central Tuber Crops
Research Institute identified a Nigerian variety and the wild species,
Manihot caerulescens, as resistant to both the Indian and Sri Lankan
mosaic viruses. Researchers have used those two donor parents and
crossed them with high-yielding local varieties to produce several
promising lines resistant to CMD, one of which has become popular
in the industrial cassava belts of Tamil Nadu9.
Root rots occur mainly in poorly drained soils during very intense
rainy periods, and are common in Africa, Asia and Latin America.
They are caused by a wide range of fungal and bacterial pathogens,
Chapter 6: Pests and Diseases 79
and lead to loss of leaves, dieback in stems and shoots, and root
deterioration, either as the crop grows or during post-harvest storage.
Farm tools and plant residues left in fields post-harvest are often
contaminated with disease-causing fungi and are sources of spores
that infect new plants.
In trials in Colombia’s Amazon region, smallholder farmers
eliminated cassava root rot using simple “Save and Grow” practices.
They planted stakes taken only from healthy mother plants, used a
mixture of ashes and dry leaves as a soil amendment and fertilizer
during planting, and intercropped cassava with cowpeas3. Other
cultural practices that control root rots include:
 If no disease-free planting material is available, immerse stakes in
hot water for around 50 minutes
 Plant on light-textured, moderately deep soils with good internal
drainage
 Improve drainage by reducing tillage and using surface mulches
 Rotate cassava with cereals or grasses
 Uproot and burn diseased plants
An effective biological control for root rot is immersion of the
stakes in a suspension of Trichoderma viride, a fast-growing species
of soil fungus that parasitizes the vegetative tissue of other soil-borne
fungi3, 10. In experiments in Nigeria, two groups of stored cassava
roots were inoculated with four pathogenic fungi. One group was also
inoculated with a culture filtrate of T. viride. Over a period of three
weeks, the group without T. viride suffered an incidence of rot ranging
from 20 to 44 percent; in the group inoculated with the biocontrol
agent, there was a drastic reduction in the range and number of the
target fungi, with the incidence of rot ranging from zero to 3 percent
after three weeks. Inoculation with T. viride rendered unnecessary
repeated spraying with synthetic fungicide11.
Control of major insect pests
A
round 200 species of arthropod pests have been reported on
cassava. Of these, some are specific to the crop, while others
attack other crops as well. The greatest diversity of cassava insect
pests is found in Latin America, where they have co-evolved with the
crop. However, cassava pest problems are not necessarily more serious
80 Save and Grow: Cassava
in Latin America – many harmful insects are kept under control by
predators and parasitoids, which have co-evolved over the centuries4, 5.
Whiteflies feed directly on young cassava leaves and are also a virus
vector, making them probably the most damaging insect pest in all
cassava-producing regions. In Latin America, 11 whitefly species have
been reported on cassava, including Aleurotrachelus socialis, A. aepim
and Trialeurodes variabilis, which cause most damage. The whitefly
Bemisia tabaci, the vector of cassava mosaic disease and cassava
brown streak disease, is found in most of sub-Saharan Africa and
now in India. It is also present in Latin America, but does not feed on
cassava. Another species, Aleurodicus disperses, or spiralling whitefly,
Bemisia tabaci transmits
is found in India, Lao PDR and Thailand, as well as in Africa, and can
serious viral diseases to
cause serious damage and yield losses.
cassava plants
Although many farmers use insecticides to control whitefly
infestations, spraying is usually ineffective – A. socialis whiteflies, for
example, double their numbers in less than five days. Not spraying insecticide, on the other hand, allows biological control by the whitefly’s
natural enemies, which include many
Figure 28 Mean number of adult whiteflies
species of parasitoids, predators and
on cassava leaves, Cameroon
entomopathogens.
40
A two-year experiment in Cameroon
Cassava
found that intercropping cassava with
Cassava
maize and cowpeas was associated
+maize
with a drop of 50 percent in the adult
30
+cowpea
whitefly population and a 20 percent
reduction in the incidence of cassava
mosaic disease (Figure 28)12. Research
in Colombia suggests that intercrop20
ping with cowpeas depresses cassava
leaf growth, making the plant less appetizing to whiteflies. Less vigorous
growth did not affect root yields – in
10
fact, yield losses were only 13 percent in
the cassava/cowpea system, but as high
as 65 percent in the monoculture13.
0
Other recommended control mea4
6
8
10
12
14
16
sures include imposing a “closed seaWeeks after planting
son”, when no cassava can be present in
the field, in order to break the whitefly’s
Source: Adapted from Fondong, V.N., Thresh, J.M. & Zok, S. 2002. Spatial and temporal spread
of cassava mosaic virus disease in cassava grown alone and when intercropped with maize and/or cowpea.
J. Phytopathology, 150: 365-374.
Chapter 6: Pests and Diseases 81
development cycle (although, this may not be as effective with some
species, such as B. tabaci, that have multiple hosts). Recent trials in
Colombia indicate that planting different cassava varieties in the same
field may reduce herbivore load and increase yields in zones subject
to heavy T. variabilis attacks14.
Mealybugs feed on cassava stems, petioles and leaves, and inject a
toxin that causes leaf curling, slow shoot growth and eventual leaf
withering. Yield loss in infested plants can be up to 60 percent of the
roots and 100 percent of the leaves. Of the approximately 15 species
of mealybug that attack cassava plants, two – Phenacoccus herrini
and P. manihoti – cause major damage to cassava in Latin America.
In the early 1970s, P. manihoti was accidentally introduced into
sub-Saharan Africa, where it had no natural enemies, and spread
rapidly throughout the region’s cassava growing areas. The mealybug
population was brought under control by the introduction of several
natural enemies from South America. The most effective predator
was Anagyrus lopezi, a tiny wasp: the female wasp lays its eggs in the
mealybug and the growing larvae kill their host.
P. manihoti was recently introduced inadvertently into Thailand
and within a year it had spread throughout the country. At its peak, in
May 2009, it affected 230 000 ha of Thai cassava-growing land. The
outbreak devastated the 2010 cassava harvest, which fell to 22.7 million tonnes, from a record of 30 million tonnes the year before.
How Thai authorities and farmers responded to the 2009 mealybug
outbreak provides an excellent example of the effectiveness of biological pest control. To avoid new outbreaks, farmers were advised not
to plant cassava in the late rainy season and early dry season, and to
soak stakes in an insecticide solution before planting. They were also
warned to avoid spraying insecticides on the plants themselves –
experience had shown that spraying provoked the pest’s resurgence.
To control outbreaks, researchers identified several native predators
and parasites but concluded they were unable to effectively reduce the
mealybug population. They suggested the use of Anagyrus lopezi, the
wasp that had successfully controlled the mealybug in Africa in the
1970s. In September 2009, some 500 adults of A. lopezi were handcarried to Bangkok from IITA’s Biological Control Centre in Benin.
After quarantine laboratory tests and field trials, the government
began large-scale multiplication and distribution of the wasp. By May
2012, almost 3 million pairs of A. lopezi had been released throughout
Mealybugs have
devastated cassava fields
in sub-Saharan Africa
and Thailand
Natural enemy of cassava
mealybugs – the tiny
wasp Anagyrus lopezi
82 Save and Grow: Cassava
Figure 29 Area infested by cassava mealybug in Thailand, 2009-2012 (‘000 ha)
250
1 Anagyrus wasp imported from Benin
2 Wasp undergoes trials
4
200
3 Wasp released in 25 villages
3
4 Wasp released nationwide
1
150
100
50
2
2009
2010
2011
30 Jul
9 Dec
15 Jan
18 Jan
24 Dec
8 Dec
15 Jan
14 May
0
2012
Source: Rojanaridpiched, C., Thongnak, N., Jeerapong, L. & Winotai, A. 2012. Rapid response to the accidental introduction of the mealybug, Phenacoccus manihoti, in Thailand.
Factsheet prepared for FAO. (mimeo)
the infested cassava area. The biological control campaign was highly
successful – the infested area was reduced to 170 000 ha in 2010, to
64 000 ha in 2011 and just 3 300 ha in 2012 (Figure 29)15.
Current recommendations for the control of cassava mealybugs
include:
 Conserve the population of natural enemies by not spraying
synthetic pesticide
 If necessary, treat planting material with a solution using a locally
registered and recommended insecticide
 Monitor cassava plantations every 2 to 4 weeks to detect focal points
of infestation
Remove
and burn the infested parts of plants

 Avoid the movement of planting material from one region to another
 Minimize the movement of planting material from infested to
non-infested fields
Cassava mites are an important insect pest in all producing regions.
The cassava green mite, Mononychellus tanajoa, causes the most
damage to cassava in Latin America and sub-Saharan Africa, especially
Chapter 6: Pests and Diseases 83
in lowland areas with a prolonged dry season. It feeds on the underside
of young leaves, which become white-yellow, deformed and smaller.
The mite can cause root yield losses of up to 80 percent. Another
green mite species, M. mcgregori, was recently reported in Cambodia,
China and Viet Nam. Although it may not be as aggressive as M.
tanajoa, it could cause serious damage owing to the lack of primary
natural enemies.
The introduction of green mites on cassava imported from Latin
America in the early 1970s devastated Africa’s cassava production. To
bring the mite under control, entomologists at IITA and CIAT first
identified its area of origin in South America and its natural enemy,
another mite, from Brazil. The Brazilian mites survived in Africa but
their diffusion was very slow.
The solution was another predatory mite, Tetranychus aripo, which
spread rapidly in African farmer’s fields and did not have a voracious
appetite for green mites – an advantage, since it allows enough green
mites to survive and prevent the predatory mites from dying out. As
well as reducing the damage caused by green mites throughout Africa,
T. aripo has contributed substantially to the science of biological
control and to the knowledge of how mites work in complex food
systems16.
Many species of red spider mites have been observed on cassava
in all three cassava-producing regions. It is the most prevalent dry
season pest of cassava in Asia, where the most common species are
Tetranychus urticae and T. kanzawai. Yield losses range from 18 to
almost 50 percent. Red mites feed mainly on the underside of leaves,
but attack old leaves at the base of the plant, causing considerable
webbing. Further research is urgently needed to identify the most
effective natural enemies of red spider mites.
Current recommendations for the control of cassava mites include:
 Plant resistant or tolerant varieties, if available
 In endemic areas, treat stakes with a recommended, locally approved
insecticide
 Promote good establishment by planting early in the wet season
 Apply adequate and well-balanced fertilizers to improve plant vigour
 Apply foliar sprays with water at high pressure to reduce mite
populations
 Strictly enforce quarantine regulations
Other natural enemies
of insect pests worth
protecting: Coccinellidae
beetles (top) and the
African lacewing
84 Save and Grow: Cassava
Other important pests that are found only in Latin America are
the cassava hornworm, burrowing bugs, leaf-cutter ants, shoot flies
and fruit flies. Great care needs to be taken to avoid accidentally
introducing those pests from Latin America to Africa and Asia, where
they have no natural enemies and could, therefore, do great damage.
A newly identified menace in Asia – found in Cambodia, Lao PDR,
the Philippines, Thailand and Viet Nam – is witches’ broom disease,
which is thought to be caused by a phytoplasma.
Some cassava pests and diseases have also been accidentally
introduced on other plant species closely related to cassava, such
as Jatropha curcas, which is used as “living fences” in Asia and has
become popular recently as a source of biofuel. Special care must be
taken in moving vegetative planting material of related species between
countries, and large Jatropha plantations should not be located in
cassava growing regions.
Weed management
C
ompared to many other crops, the initial growth of cassava is slow.
That, combined with the wide spacing between planted stakes,
gives weeds a chance to emerge and compete for sunlight, water and
nutrients. In the first four months after planting, cassava can easily be
overwhelmed by competition from narrow-leaf grassy weeds and from
broad-leaf weeds, which include many leguminous plants. In East
Africa, weeds are often a more serious production constraint than
insect pests or diseases and can reduce yields by about 50 percent17.
In Nigeria, farmers spend more time on weeding than on any other
aspect of crop production18.
Once the cassava canopy has closed, it will shade out most weeds
and keep the field almost completely weed-free19, 20. Six to eight
months after planting, when cassava starts to shed many leaves (especially during the dry season), weeds may reappear, but this generally
does not seriously affect yields. Excessive late weed growth may make
harvesting more difficult, but can also protect the soil from erosion if
post-harvest rains are heavy.
Chapter 6: Pests and Diseases 85
“Save and Grow” cultural practices can provide an effective defence
against weeds. While cultural controls may not be 100 percent effective, they do help in reducing weed competition, and thus the need
for mechanical or chemical weeding21. Cultural control begins with
selection of high-quality planting material from varieties with vigorous
early growth and tolerance or resistance to important diseases and
pests. High planting density and the correct type and rate of fertilizer,
applied in short bands next to the planted stakes, can stimulate early
crop growth and rapid canopy closure. Planting in the dry season
under drip irrigation can also encourage the growth of cassava but
not that of weeds.
To prevent weed emergence, the soil should be covered with a
thick layer of mulch, such as rice straw or maize residues. Another
“Save and Grow” recommendation is to intercrop cassava with fastgrowing plants, such as melons, squash,
Figure 30 Effect of hand weeding on fresh cassava root
pumpkins, common beans, groundnuts, yield 280 days after planting, Colombia (t/ha)
soybeans, mungbeans and cowpeas. As 25
those are short-duration crops, they can be
harvested after about 3 to 4 months, when 20
the cassava canopy closes and weeds are
shaded out. While intercrops may reduce 15
cassava root yields, they markedly reduce
weed growth, and offer an eco-friendly – and 10
less expensive – alternative to spraying with
herbicides. A study in Nigeria of legume 5
cover crops in a mixed cassava/maize system
reported significant improvements in cassava
root yields when velvet beans were grown to 0
0
1
2
3
4
Chemical
suppress weeds18.
Number of hand weedings
control
Many smallholder cassava farmers use
Source: Annex Table 6.1
mechanical control measures. Most commonly, they remove weeds by hoeing, starting about 15 days after
planting, or after emergence if the cassava is planted horizontally.
Research in Colombia (Figure 30) found that with hand-weeding at 15,
30, 60 and 120 days after planting, cassava root yields were 18 tonnes
per ha, only 8 percent less than those obtained when weeds were
controlled with herbicides. When weeds were not controlled at all,
yields fell to just 1.4 tonnes.
Weeds growing between the rows can also be incorporated
into the soil using an oxen- or buffalo-drawn cultivator or, where
86 Save and Grow: Cassava
available, tractors equipped with cultivator blades. In the absence
of both machinery and draught animals, farmers in Thailand use
a manually-drawn cultivator, known as a “poor man’s plough”. In
Viet Nam, farmers use a contraption made from the handlebar and
front wheel of a bicycle, with a cultivator blade attached behind the
wheel. This operation is usually followed by hand weeding with a hoe
between the plants in the row.
On larger farms or when labour is unavailable or is too expensive,
weeds are often controlled with herbicides. Many herbicides are highly
toxic and, being water soluble and persistent in the environment, can
be washed away to contaminate ground and surface water. Farmers
need to exercise care in the choice of the herbicide to be used and
follow the advice of local plant protection specialists.
Pre-emergence herbicides do not kill existing weeds. Instead, they
prevent weed seeds in the soil from emerging or, at least, reduce their
rate of growth. Pre-emergence herbicides are either incorporated into
the soil before planting or applied on the soil surface with a knapsack
sprayer immediately after planting. Pre-emergence herbicides that are
selective for cassava can be applied over the vertically planted stakes
without affecting cassava sprouting or yield.
The application of pre-emergence herbicides can maintain a cassava
field almost weed-free for 6 to 8 weeks after planting. Farmers may
apply a mixture of two herbicides – one that controls the grassy weeds
and one the broad-leaf weeds. A lower dosage is recommended on
light-textured soils, while a higher dosage may be needed in heavy
soils, such as loamy clays. Special care needs to be taken when cassava
is grown in association with other crops, because the pre-emergence
herbicides normally used for cassava may harm the intercrop.
At about two months after planting, weeds may need to be
controlled again to reduce competition with cassava. This is usually
done by hoeing or using an animal- or tractor-mounted cultivator,
depending on the height of the growing cassava plants and the extent
of canopy closure. When most of the weeds are grassy species, it is
also possible to apply a selective post-emergence herbicide, which
kills grasses but does not affect the cassava plant. Post-emergence
herbicides can be used about 4 to 5 months after planting, when
some bottom leaves start to drop off. They should only be applied on
windless days and with a nozzle shield to prevent spray from reaching
the cassava stems or leaves.
Chapter 7
Harvest,
post-harvest and
value addition
Food for the household, feed for livestock,
and raw material for a wide array
of value-added products, from coarse flour
to high-tech starch gels – cassava
is a truly multipurpose crop.
Chapter 7: Harvest, Post-harvest and Value Addition 89
O
ne of the major positive attributes of cassava
is that it does not have a specific harvesting
period. Roots may be harvested any time between six months and two years after planting.
During periods of food shortage, they can be harvested
whenever needed, often one plant – or even one root – at
a time. For human consumption, harvesting usually takes
place at about 8 to 10 months; for industrial uses, a longer
growing period generally produces a higher root and starch
yield. Once harvested, roots can be consumed directly by
the farm household, fed to livestock or sold for processing
into a wide array of value-added products, ranging from
coarse flour to high-tech modified starch gels.
The root is not the only part of the plant that can be
put to good use. In Africa, cassava leaves are cooked as a
vegetable. In many countries, the green part of the upper
stem, including leaves and petioles, are fed to cattle and
buffaloes, while the leaf-blades are fed to pigs and chickens.
In China, Thailand and Viet Nam, fresh leaves are used
for raising silkworms. Stumps are burned as fuelwood,
and woody stems are ground-up and used as a substrate
for growing mushrooms.
Harvesting roots and plant tops
C
assava roots are generally harvested by cutting off the stems about
20 cm above ground, then lifting the whole root system out of the
ground by pulling on the stump. If the soil is too hard or the roots are
too deep, it may be necessary to dig around the roots with a hoe, spade
or pick to remove the soil, avoiding damage to the roots in the process.
To harvest their cassava, Thai farmers have developed a metal tool
that is attached to a pole and used as a lever. It works best in loose or
light-textured soils. In heavier soils, which can become very hard in the
dry season, a harvesting blade attached to a tractor is sometimes used.
The blade cuts through the soil just below the roots and the forward
movement of the tractor pushes the root clumps to the surface. The
roots are then cut from the stump and placed in baskets or sacks for
transport.
Bringing home the
harvest. Worldwide,
cassava growers produced
more than 280 million
tonnes of fresh roots
in 2012
90 Save and Grow: Cassava
The harvest of large cassava fields is often done by middlemen
who employ teams of workers and use trucks to transport the roots
to markets or processing plants. In Viet Nam, roots are often carried
home in two baskets hanging on a shoulder pole; in Lao PDR, farmers use bamboo shoulder baskets. In China, the harvested roots are
generally transported in a wagon attached to a 2-wheel tractor, while
in Thailand, many farmers use a small agricultural truck.
After the root harvest, plant tops are often left to dry on the ground
and later incorporated in the soil to help maintain its fertility (see
Chapter 5, Crop nutrition). However, farmers can greatly increase
the total amount of cassava foliage available for feeding to animals
by cutting the green tops every 2.5 to 3 months during the plant’s
growth cycle. After each pruning, the remaining stems will sprout
again and produce another crop of leaves within 2 to 3 months. For
maximum foliage production, cassava stakes should be planted with
closer spacing, of about 60 x 60 cm.
Young leaves harvested at regular intervals during the cassava
growth cycle tend to have a higher protein and lower fibre content than
those collected at the final root harvest, when plants are normally 11 to
12 months old. The younger leaves are more palatable and provide a
higher quality feed. Similarly, leaf meal containing only leaf-blades has
a higher protein and lower fibre content than meal that also contains
petioles and green stems.
In an experiment in Thailand, total dry leaf yield was 710 kg per
ha when leaves were harvested only at the time of root harvest, at
11.5 months after planting (Annex table 7.1). But the yield increased
to 2.6 tonnes when leaves were cut five times during the same period.
The total leaf protein yield also increased, from 170 kg with only one
leaf harvest to 650 kg, similar to a good crop of soybeans1,  2. However,
as the frequency of leaf cutting increased, the final root yield dropped,
from around 40 tonnes per ha when leaves were harvested only at
the time of the root harvest, to less than 25 tonnes when leaves were
harvested a total of five times2. Depending on the cost of labour and
the relative prices of fresh roots and dry leaves, this system may or
may not be economic.
Harvesting the plant tops 4 or 5 times during a one-year growth
cycle also removes a large amount of nutrients – especially nitrogen –
from the field, and would not be sustainable without the application
of large amounts of mineral fertilizer to maintain soil fertility.
Chapter 7: Harvest, Post-harvest and Value Addition 91
Post-harvest uses and value addition
Food for direct consumption
Young cassava leaves are regularly picked and cooked for human
consumption in several African countries, notably Cameroon, the
Democratic Republic of the Congo, Liberia and the United Republic of
Tanzania. The tender leaves contain up to 25 percent protein, on a dry
matter basis, and are a valuable source of iron, calcium, and vitamins
A and C3. The essential amino acid content of cassava leaf protein is
similar to that found in a hen’s egg. The market value of cassava leaves
in areas where they are consumed is often higher than that
of the roots, indicating that their
sale contributes significantly to
farm household incomes4.
Cassava leaves are prepared by
removing the hard petioles, then
pounding the blades and young
petioles with a pestle and mortar,
and boiling the resulting pulp
for about 30 to 60 minutes. That
process eliminates cyanogens
and makes the leaves safe to eat.
However, prolonged boiling also
results in considerable loss of
vitamin C5.
Cassava roots deteriorate
rapidly and must be processed
within a few days of harvesting.
In many parts of Brazil, fresh
roots are grated and the liquid,
which contains much of the roots’ cyanide content, is pressed out.
The semi-dry mash is then roasted to produce farinha, a coarse flour
that is spread on many Brazilian dishes. In Africa, grated roots are
fermented before being roasted on a hot plate to produce a granulated
flour called gari, or sun-dried and milled into flour, which is mixed
with water to produce a stiff dough called fufu.
Steaming is used in Côte d’lvoire and Benin to make another
granulated cassava product, called attiéké. In the Democratic Republic
of the Congo, pounded cassava flesh is wrapped in banana leaves and
In Central Africa, tender
young cassava leaves
are regularly picked and
cooked as a protein-rich
vegetable
92 Save and Grow: Cassava
steamed for several hours to make cassava bread or sticks, called chickwangue or kwanga, which are served with soups, stews and sauces.
In Indonesia, peeled roots are sliced lengthwise then sun-dried.
The dry chunks, called gaplek, are then stored or sold in market stalls.
When needed, gaplek is pounded into flour, which is swirled around
with a little water to produce small granules the size of rice grains.
The granules, called tiwul, are steamed, either separately or together
with rice, and eaten as a “rice extender” when there is not enough
rice to feed the family. Another popular snack in Indonesia, called
krepek, is made by washing peeled roots and thinly slicing them with
a hand- or electric slicer. The slices are placed in cold water, drained
and then fried in hot oil for a few minutes. Once cooked, they are
covered with a mixture of hot or sweet spices and sold in small plastic
bags by hawkers or in local markets.
High quality cassava flour (HQCF) is cassava flour that has not been
fermented and can be used as an alternative to wheat flour and other
starches in bread and confectionary. The processing of cassava roots
into HQCF involves peeling, washing, grating, pressing, disintegration,
sifting, drying, milling, screening, packaging and storage.
Although markets for unfermented high quality cassava flour are
emerging in sub-Saharan Africa, the challenge is linking them to
large numbers of small-scale growers whose output is highly variable
in quality. Where the value chain is relatively well established (for
example, in Nigeria and Ghana), artificial dryers capable of processing 1 to 3 tonnes of HQCF per day could help to locate intermediary
processing closer to the sources of fresh cassava roots. Processors could
also provide intermediate bulking, aggregation and transportation
services, and ensure acceptable quality of products to be delivered to
the end-use market6.
Native starch is extracted from cassava roots in some countries,
mainly in Asia, and used in food products. If properly extracted,
cassava starch is pure white, with low levels of fat and proteins and
a non-cereal taste, which is desirable in many food products7. Starch
extraction can be done at almost any scale – in backyard artisanal
production units and large-scale fully mechanized factories. Many
artisanal starch production units still operate in Cambodia, India,
Indonesia and Viet Nam. In backyard processing, cassava roots are
hand-peeled, washed, grated and mixed with water. The starch water
is passed through a cloth sieve to remove the fibre, and the suspended
starch is then left to settle in tanks or flow channels. After the surface
Chapter 7: Harvest, Post-harvest and Value Addition 93
liquid is siphoned off, the wet starch is collected, crushed and spread
out on bamboo mats or on concrete floors for sun-drying. In artisanal
production systems, daily starch output ranges from 50 to 60 kg of
starch per worker, while semi-mechanized processing can yield up to
10 tonnes a day8.
In some parts of Colombia, wet starch is left to ferment for a few
days before being sun-dried. This produces sour starch, which is the
main ingredient in buns called pan de bono. In Tamil Nadu State,
India, wet starch is collected, crushed and then shaken on a hemp
cloth to form small starch balls, which are sieved and steamed for
a few minutes to form tapioca pearls. In Indonesia, cassava starch is
mixed with shrimp paste, food colouring and water and then extruded
and thinly sliced by hand. The slices are steamed on bamboo screens
for 5 to 15 minutes, after which they are sun-dried on a patio floor for
half a day, producing hard chips known as krupuk. When deep-fried,
krupuk swell into brittle soft crackers, which are a popular snack that
accompanies almost every meal.
Starch extraction produces a considerable quantity of useful
residues. Root peelings can be recycled as fertilizer and animal feed.
Once dried, the discarded fibre can be sold as flocculent to the mining
industry, while low-density starch lost during sedimentation is used
as pig feed8.
Industrial uses
In countries such as Thailand and China, much of the native cassava
starch is further processed to make a range of modified starches, for
incorporation in food products or use as feedstock for production
of sweeteners, fructose, alcohol and monosodium glutamate. Along
with high quality cassava flour, modified starch is also used in the
manufacture of plywood, paper and textiles.
In fully mechanized starch factories in China and Thailand, cassava
roots are thoroughly washed, then cut and rasped, after which the
mash is mixed with water several times to release the starch granules.
The “starch milk” – the water containing suspended granules – is
then separated from the pulp, after which the granules are separated
from the water by sedimentation or in a centrifuge. At that point, the
starch requires solar or artificial drying to remove moisture before
being milled, sifted and packed into 50 kg bags or one-tonne sacks.
In modern, fully mechanized starch extraction plants, daily output
is as high as 300 tonnes8.
94 Save and Grow
Increasingly, cassava is also being used for production of fuel
ethanol. Fresh roots or dried chips are cleaned, washed, crushed and
mixed with water, heated with liquefying enzymes, then cooled with
other enzymes, which convert the starch to sugars. The sugars are fermented with yeast to produce ethanol, which is concentrated through
distillation and finally dehydrated in a molecular sieve to produce
99.5 percent pure anhydrous ethanol. It can be blended with gasoline
to produce “gasohol” with 10 percent, 20 percent or even 85 percent
ethanol. Cassava-based fuel ethanol factories are now operating, or
are under construction, in Cambodia, China, Colombia, Thailand
and Viet Nam. Conversion to ethanol will become one of the major
uses of cassava fresh roots and dry chips in the future, especially in
China9.
Two recent cassava mutations could expand considerably cassava’s
use in industrial applications7. The first, an induced mutation, has very
small starch granules which offer a faster rate of hydrolysis – thus
reducing the cost of producing ethanol or sweeteners – than other
major starches. The second, a spontaneous mutation, produces an
amylose-free “waxy” starch that has great advantages when used in
frozen foods. Gels made from the starch have excellent water retention during defrosting, a highly desirable characteristic for the food
industry.
Animal feed
Both the roots and leaves of the cassava plant can be used as on-farm
animal feed or as an ingredient in commercial animal feed. Because
of their high cyanide content, however, fresh roots or leaves can be fed
to animals only in very small quantities. Cassava roots are chipped
or sliced, while leaves are chopped into small pieces. Before being fed
to animals, the cassava pieces are spread out on a floor overnight in
order to release some of the cyanide by evaporation. The root chips
and leaf pieces can also be sun-dried to 12 to 14 percent moisture
content, then stored for future use. Alternatively, the chopped pieces
of roots and leaves can be packed tightly in plastic bags or air-tight
containers and fermented to make silage (see p.96). Both sun-drying
and ensiling will release most of the cyanide, making those products
safe as feed for pigs, cattle, buffaloes and chickens.
Dried cassava chips are produced by first washing, or at least slightly
cleaning, the roots in a rotary drum to remove soil and some of the
outer skin. The roots are then chipped and spread out on a concrete
Chapter 7: Harvest, Post-harvest and Value Addition 95
floor for sun-drying, and turned regularly with a rake to promote
uniform drying. Normally it takes up to four days of sun-drying to
make dried chips with about 12 to 14 percent moisture content.
In Viet Nam, cassava roots are often roughly peeled and sliced by
hand before sun-drying in courtyards or along roadsides. In Thailand,
many farmers take their cassava to drying yards, where the roots are
first dumped into the hopper of a diesel-powered chipping machine.
The chipped roots are then spread over large concrete floors for sundrying and turned over regularly by a vehicle with a large rake. After
two or three days of drying, the chips are piled up by a grader and
loaded in bulk onto trucks. Some are further processed into pellets,
mainly for export.
Although the need for rapid chipping and drying adds to the
complexity of production, small farmers in Asia and their marketing partners, who provide cassava chips for the animal feed export
industry, have shown that with adequate infrastructure, smallholder
produce can be dried locally and reach market chains with relatively
low losses10.
Chips are usually sold directly or milled into a powder that can
be mixed with other ingredients – such as soybean meal, full-fat
soybeans, fishmeal or other protein sources – to make a nutritious
animal feed that is usually supplemented with methionine, vitamins
and minerals. When the diet is well-balanced, in terms of energy and
protein, the performance of pigs is very similar to that obtained with
a diet based on maize or broken rice. Cassava meal is highly digestible
and naturally contaminated with lactic acid bacteria and yeast, which
improve the micro-flora in the digestive tract of animals. At low levels,
hydrogen cyanide in cassava feed increases the efficiency of an enzyme,
lactoperoxidase, which is a natural antibiotic that kills mycotoxins
in the animal’s body and milk. Animals raised on cassava diets have
generally good health, good disease resistance and a low mortality
rate. They require few if any antibiotics in their feed11.
Dry cassava leaf meal (also known as “cassava hay”) is usually
obtained by cutting the plant tops at 2.5 to 3-month intervals during
the cassava growth cycle. The best quality foliage meal contains a
large proportion of leaves and only very young stems, and is obtained
from plants or shoots that are less than three months old. After
harvesting, the foliage is chopped and spread out on a concrete floor
for sun-drying. The moisture content needs to be reduced from about
96 Save and Grow: Cassava
70 percent to 12 to 14 percent so that the foliage can be milled and
stored.
Owing to its high fibre content, cassava foliage meal is suitable
mainly for ruminants. Research has shown how supplementation with
1 to 2 kg of cassava hay per animal per day increases the milk yields
of dairy cows and boosts levels of thiocyanate in the milk, which may
enhance milk quality and storability. Condensed tannins in the foliage
meal also reduces gastro-intestinal nematodes, indicating that the meal
may act as an anti-helminthic agent12. For non-ruminants, dry cassava
foliage meal is best limited to 6 to 8 percent of the feed for growing pigs
and to less than 6 percent of that for broilers. In broilers, the inclusion
of cassava foliage meal is useful mainly as a natural pigmenter – the
high content of xanthophyll pigments (500-600 mg/kg) improves the
pigmentation of skin in broilers and that of egg yolks13.
Leaf silage is made by mixing chopped leaves with 0.5 percent salt
and 5 to 10 percent cassava root meal or rice bran, and then placing
the mixture in large plastic bags or air-tight containers. The leaves
are compacted to expel all air and the bags are sealed. Under these
anaerobic conditions, the leaves start to ferment, resulting in a sharp
drop in pH, as well as in cyanide content. After about 90 days of
fermentation, the silage is ready to be fed to animals, usually pigs and
cattle. The silage can be stored in tightly sealed bags for at least five
months without spoiling. The ensiled leaves contain about 21 percent
crude protein and 12 percent crude fibre. They also contain 200 ppm
hydrogen cyanide, compared to more than 700 ppm before ensiling.
In experiments conducted in Viet Nam, a diet containing 15 percent
ensiled cassava leaves improved the daily weight gain of pigs and
reduced their feed cost by 25 percent14.
Chapter 8
The way forward
Governments need to encourage
smallholders’ participation
in a sustainable cassava development
agenda, and support research
and extension approaches
that “let farmers decide”.
Chapter 8: The Way Forward 99
T
his guide has presented a range of science-based “Save and
Grow” farming practices that will contribute to the sustainable intensification of cassava production. They provide the
basis for competitive, profitable production systems that
boost productivity per unit of input, while protecting and nurturing
the agro-ecosystem.
However, those recommendations will have little impact unless they
are incorporated in large-scale agricultural development programmes
and are widely adopted by farmers. For that to happen, governments
will need to make policies that encourage the participation of all
stakeholders, and particularly smallholder producers, in a sustainable
cassava development agenda. Successful adoption of “Save and Grow”
will also depend on farmers’ understanding of agro-ecosystem functions and on their capacity to make wise technology choices. That will
require significant strengthening of extension services and innovative
approaches to the transfer of knowledge and technologies1.
Policies for sustainable intensification
S
mallholder farmers raise crops and livestock primarily to feed their
families and to earn enough income from sales to cover expenses,
such as education and health care. They often have a short planning
horizon, focused on satisfying their immediate needs, rather than
ensuring the long-term sustainability of their farming enterprise.
Farmers need to become aware that some of their current practices
jeopardize their natural resource base and, with it, their future productivity, income, livelihood and food security.
Locally, negative impacts of unsustainable crop production include
the erosion, compaction and nutrient depletion of soil, the loss of
natural habitats and natural enemies of pests, and the risks posed
to farmers’ health by the excessive use of pesticide. Other farming
practices have off-farm impacts which, while not harming the farmer
directly, are nevertheless of serious concern to society at large. Those
“negative externalities” range from nitrate pollution of waterways and
flooding of downstream areas, to pesticide residues in food and the
greenhouse gas emissions responsible for climate change.
Like most people, farmers are usually reluctant to spend time
and money solving problems that do not directly affect them. The
100 Save and Grow: Cassava
challenge facing cassava-producing countries, therefore, is to set
policies and create an institutional environment that facilitate sustainable intensification of cassava production, while expanding market
opportunities for small-scale cassava growers.
Policymakers should begin with an analysis of the current state of
the cassava subsector. In most countries, cassava production is still
labour-intensive and largely subsistence-oriented, with low levels of
technology uptake, high production and post-harvest losses, and weak
linkages to markets.
Transforming the subsector, in a way that ensures food security,
income generation and economic diversification, requires the identification of profitable value chains and market preferences, strategies
for reducing price variability on the demand side, and options for
enhancing the quality, volume and reliability of production on the
supply side. Improving market access and competitiveness will require
vertical and horizontal coordination, strategic market-led research,
and mechanisms for stimulating innovation and sharing knowledge,
including farmers’ practical know-how. As policymakers encourage
higher levels of value addition, a major effort will be needed to integrate
small-scale growers into the cassava marketing chain.
While there is no “one-size-fits-all” set of recommendations, it is
possible to identify the key features of enabling policies and institutions
for sustainable intensification of smallholder cassava production.
Promote “Save and Grow” farming approaches and practices.
Cassava growers should be encouraged to phase out slash-and-burn
production, and cultivate smaller areas of flat and more fertile land
nearer to their homes, transport and markets. Continuous production
on the same land will help to reduce forest clearing, the annual burning
of vegetation (which emits large amounts of carbon dioxide into the
atmosphere), and the drudgery of carrying heavy loads of cassava
roots over long distances. The steeper land can be returned to forest
vegetation or used for perennial fruit trees, rubber or coffee.
To be sustainable, however, intensive systems of cassava production
need to use good quality planting material and ecosystem-based
approaches to soil fertility management and to insect pest, disease
and weed control. In many countries, low-input cassava production
systems already incorporate key “Save and Grow” practices, such as
reduced or zero tillage, the use of cover crops and mulches, and mixed
Chapter 8: The Way Forward 101
cropping. Extension and advisory services – organized by the public
sector, the private sector or NGOs – will be crucial in improving
those practices by ensuring access to relevant external knowledge and
linking it to the wealth of knowledge held by smallholders themselves.
Participatory extension approaches will be needed to support farmers
in testing and adapting technologies. New channels of communication,
including radio, mobile phones and the Internet, can help to reduce
the transaction costs of extension.
Cassava growers may also need incentives – for example, payments
for environmental services – to adopt new farming practices and to
manage other ecosystem services besides food production, such as soil
conservation and protection of biodiversity. Adoption of integrated
pest management can be promoted by removing “perverse subsidies”
on synthetic pesticides, regulating their sale, and providing incentives for local production of biopesticides and insectaries for natural
predators.
Facilitate improvements in the input supply chain. Disposable
household income is too low to allow many small-scale farmers
to move from low-input/low-output production to more intensive
cultivation of cassava. Action is needed, therefore, to make improved
planting material, mineral fertilizer and other inputs more affordable
to smallholders. Governments should encourage private investment
in the production of inputs, and establish credit lines to enable private
suppliers to organize bulk procurements that ensure the availability
of inputs in time for planting. Where necessary, the quality of inputs
should be routinely tested to prevent the sale of bogus products. To
avoid the inappropriate use, wastage and negative environmental
impacts of mineral fertilizer, its distribution should be accompanied
by training and extension advice.
Institutions that facilitate participation – such as farmer groups,
community organizations and development NGOs – can also help to
reduce the transaction costs of accessing input markets, while “smart
subsidy” voucher schemes could be introduced to allow smallholders
to purchase fertilizer and planting material at below-market prices.
Although subsidies are attractive to smallholders, they can create
dependency; in the long-term, group-based revolving credit funds will
be a more sustainable source of financing. Once cassava growers see
how fertilizer and improved varieties can help to increase their yields
and income, they will want to buy more – and will have the financial
102 Save and Grow: Cassava
means to do so. That, in turn, stimulates competition, which lowers
prices and makes inputs more affordable.
Control pest and disease threats with resistant varieties and
strict quarantine regulations. As cassava production is intensified, continual cropping risks provoking an upsurge in pests and
diseases, which are already one of the most serious constraints to
increased productivity. Rather than resorting to chemical pesticide,
cassava intensification programmes should promote integrated pest
management, which draws on resistant cultivars, biological control
agents, bio-pesticides and habitat management to protect crops,
conserve biodiversity and safeguard the environment and human
health. All germplasm and varieties deployed should be resistant to the
predominant pathogen populations present in each specific country,
agro-ecozone and farming system. In the absence of a formal seed
supply, quality planting material should be made available to growers
through community systems of multiplication and distribution.
With increased international movement and exchange of cassava
germplasm, improved phytosanitary measures will be needed to
ensure that planting material is free of pests and diseases. Sensitive and
robust detection and diagnostic methods to prevent the movement of
pathogens are essential for improving quarantine security and bringing
national phytosanitary regulations into line with international trade
conventions and protocols. The transfer of cassava germplasm should
be carefully planned in consultation with quarantine authorities and
should be in amounts that allow adequate testing. Cassava germplasm
should only be moved as seed, pathogen-tested in vitro material, or
as cuttings from re-established pathogen-tested in vitro material that
has been grown under containment2.
Support cassava research and technology development. Applied
agricultural research can facilitate the transformation of cassava
cropping systems by helping to develop varieties with disease- and
pest-resistance and more desirable commercial traits, water-efficient
irrigation technologies, and appropriate farm machinery, especially
for land preparation, planting and harvesting. Policies should help
to foster public-private partnerships for technology development,
and link them to markets in order to facilitate the up-scaling of successful innovations. For example, Thailand’s Tapioca Development
Institute, which was set up with government funding but operates
Chapter 8: The Way Forward 103
as an independent non-profit organization, is working with CIAT
and Kasetsart University to breed “waxy” starch cassava varieties
adapted to Thai growing conditions. The Latin American and
Caribbean Consortium to Support Cassava Research and Development
(CLAYUCA) is a regional network of public and private entities that
plans and coordinates research for the cassava subsector. Acting as
a facilitator of public/private alliances, CLAYUCA fosters sustainable cassava production intensification and improved access to elite
genetic material. Among recent achievements is a small-scale, low-cost
technology, easily operated and managed by smallholder farmers, for
local production of ethanol from cassava.
Improve rural infrastructure. Good physical infrastructure is
essential for the smooth operation of the cassava value chain, especially considering the need to process the roots within 48 hours of
harvesting. The poor state of rural roads in many countries not only
limits farmers’ access to inputs and financial services – it also severely
restricts their access to markets. The lack of storage and processing
infrastructure leads to high post-harvest losses, undermines market
development and discourages all stakeholders in the value chain from
producing and supplying quality-differentiated products with desirable
market traits.
Investment in road networks and in warehousing and processing
capacity in production zones will help to link small-scale cassava
farmers and processors to growth markets for intermediate cassava
products that have a longer shelf life. It will also contribute to price
stabilization, reduction of post-harvest losses and lower transaction
costs. With appropriate technology and equipment, community-level
processing plants could produce high quality cassava flour, grits and
chips for rural and urban-based industries, allowing cassava growers to
retain a bigger share of the value-addition. There is a need to develop
models for community-level bulking and grading that can assure
regular supply to potentially large urban markets. Since mechanical
drying powered by fossil fuels has often proven to be uneconomic in
isolated rural areas, processing power based on a combination of solar
energy, fossil fuel and biomass sources should be considered.
Develop value chains and markets in order to boost demand and
increase returns to producers. Initially, those markets will be local
ones for fresh roots or leaves, or small-scale processors of fermented
104 Save and Grow: Cassava
flour or low-quality starch. As markets develop and demand grows,
farmers have an incentive to grow more by intensifying production. An
increased supply of raw material provides an incentive to processors
to expand capacity and modernize their factories, which stimulates
further production increases, driving an upward spiral of rural
development. Examples of successful market development include
the rapid growth in Thailand of the production of dried cassava chips
and, more recently, of fuel ethanol for domestic markets and export.
Governments should promote private investment in cassava processing plants, and foster associations that link cassava growers and
processors, such as the Thai Tapioca Starch Association and Nigeria’s
Cassava Market and Trade Development Corporation. Cassava
industry stakeholders may need assistance in initiating industry-wide
or activity-specific associations that can help enterprises of different
sizes to work together. An active industry association can foster cooperation among value chain participants, promote grading standards,
share market information, and lobby governments to support cassava
subsector development. Industry clusters – market-driven, private
sector-oriented groups or enterprises – can be formed around such
associations to define the measures and activities needed to improve
productivity and to make the value chain work efficiently.
Planners will need to link support to the cassava subsector with
action to develop associated industries. For example, development
of cassava as a feed resource should exploit complementarities with
livestock and poultry enterprises; increasing output of high quality
cassava flour will require the strengthening of links with the bakery
industry.
Reduce farmers’ exposure to price volatility. For people whose
livelihood depends mainly on agriculture, volatility in output prices
means fluctuations in income and greater risk. Guaranteeing farmers
a reasonable price for their crops will encourage them to invest in
production. One approach is subsidies, such as the Thai Government’s
national “pledging scheme”, which set aside in 2012 some US$1.43 billion for purchasing roots from cassava growers3. More sustainable
approaches include contract farming, which helps to reduce the
transaction costs of input supply and output marketing by aggregating
small parcels of farmland. Large scale processors not only ensure an
agreed price to farmers but also provide technical services in return
for growers’ commitment to deliver all or a significant portion of
Chapter 8: The Way Forward 105
production. In the Philippines, for example, one of the country’s
leading food manufacturers offers supply contracts to farmers’
cooperatives that can consolidate at least 20 ha of land for cassava
production. It provides start-up technical advice, a guaranteed floor
price, and a marketing agreement that covers product quality, volumes
and a delivery schedule4.
Governments in developing countries should foster greater availability of crop insurance which, while it does not eliminate risk, does
mitigate losses caused by adverse weather and similar events, thus
improving risk-bearing capacity and encouraging investment in
production. While common in industrialized countries, crop insurance is very limited in the developing world and particularly so for
smallholder crops such as cassava.
Letting farmers decide
F
armers will need to be convinced that “Save and Grow” practices
are better than those they are using already and – very importantly
– that they have short-term economic benefits. Not all recommended
practices are equally useful, nor are they universally applicable.
Farmers are interested only in those practices that fit well with their
cropping systems and ways of farming. Practices that may have been
effective during trials on experimental stations may not perform nearly
as well under farmers’ local conditions.
Since most technologies have advantages and disadvantages, tradeoffs need to be made. That can best be done by farmers themselves,
rather than by researchers or extensionists. It is important, therefore,
that cassava growers be involved in all stages of agricultural research
and technology development, and are empowered to test and validate,
in their own fields, practices aimed at improving the sustainability of
cassava production. By shifting the extension paradigm from “teaching” to “learning”, two methodologies – farmer participatory research
(FPR) and farmer field schools (FFS) – have proven highly effective
in incorporating sustainable natural resource management into
smallholder production systems.
Farmer participatory research emerged in the 1990s in response to
the failure of top-down agricultural research to deliver significant
106 Save and Grow: Cassava
improvements in the well-being of low-income farmers in risk-prone
environments. The difference between FPR and the more traditional
“technology transfer” approach is that extension workers do not promote or recommend any particular practice or technology. Instead,
they provide a menu of options that farmers can test in simple trials
in their own fields, with help from research or extension staff5.
CIAT has used farmer participatory research extensively in Asia for
the development and transfer of cassava production technologies. Its
FPR programme involved farmers in 99 villages in China, Thailand
and Viet Nam, who conducted more than 1 150 trials, mostly of
improved varieties, fertilization, erosion control, plant spacing, green
manuring and the use of cassava roots and leaves as animal feed.
With FPR, members of a farmers’ group, or farmers in a particular
village or district, first diagnose the main problems encountered in
cassava production and, with assistance from research and extension
staff, consider possible solutions. From this diagnosis, they decide on
specific topics for their trials. Whenever possible, the farmers visit
experimental stations or other villages to view similar trials, or confer
with farmers who have already adopted the practices being tested.
They then select 3 to 5 alternative treatments, along with one
traditional practice, to test in simple, unreplicated FPR trials in their
own fields. If all farmers in the area use the same treatments in one
type of trial, each trial can be considered a replication, and the results
can be averaged over those replications. That improves confidence in
the results obtained.
The next step is for the farmers to design and conduct the trials,
with help from research or extension staff. The farmers manage the
trials themselves, while staff may visit occasionally to discuss progress
and help solve problems. Finally, at harvest time, all farmers in the
area, and from neighbouring areas if possible, are invited to a field day
where they view the trials and discuss the results. During the field
day, staff present the average results of the various types of trials, as
well as the production costs, gross income and net income of each
treatment. Based on this information, farmers can select those varieties
or practices that they consider most suited to their own conditions.
The FPR approach has been highly successful. An independent
impact assessment in 2003 found that, in Thailand, all of the farmers
who had directly participated in trials had adopted improved varieties,
98 percent the use of mineral fertilizer, and 80 percent soil conservation practices to control erosion. In Viet Nam, the adoption rates were
Chapter 8: The Way Forward 107
Figure 31 Farmer preferred cassava management options with
groundnut intercrop in Viet Nam (million dong)
50
Production costs
Gross income
Net income
40
30
20
10
0
Preference 1
with fertilizer, vetiver
hedgerows
Preference 2
with fertilizer, pineapple
hedgerows
Preference 3
with fertilizer, Tephrosia
hedgerows
Source: Annex Table 8.1
82 percent, 80 percent and 71 percent, respectively6. In one province
of Viet Nam, improved technologies and agronomic practices boosted
average per hectare root yields from 8.5 tonnes in 1994, when the trials
began, to 36 tonnes in 2003. The Vietnamese trials, and Asian trials
in general, have shown clearly that farmers prefer treatments which
produce both sustainable yields and the highest net income (Figure 31).
Farmer field schools encourage a process of group-based learning,
and were originally developed by FAO in the late 1980s to promote
integrated pest management in Asian rice fields. At field schools, farmers are able to deepen their knowledge of agro-ecosystem processes,
and test and validate practices that control pests and diseases and
improve the sustainability of crop yields.
The application of FFS to cassava began in Africa in the late 1990s.
The spread of new strains of the viruses causing cassava mosaic
disease and, more recently, cassava brown streak disease, has served
as an entry point for promoting IPM and eco-friendly production.
Field schools link up with programmes that distribute diseasetolerant cassava varieties and test them in multiplication fields. This
learning-by-doing approach provides the opportunity for farmers to
develop strategies to manage disease problems more effectively, while
improving their cassava production practices.
108 Save and Grow: Cassava
In the Democratic Republic of the Congo, an FAO project trained
facilitators to assist 30 field schools in Kinshasa province, where yields
of cassava had been declining owing to pest attacks, diseases and soil
nutrient depletion. Through training in the use of healthy planting
material, mulching and intercropping, the field schools helped farmers
achieve yield increases of up to 250 percent7.
In Gabon, pest and disease pressure, the lack of improved varieties, and the use of inefficient farming methods kept smallholder
cassava root yields below 8 tonnes per ha. Through field schools,
some 750 growers improved their skills in the selection of healthy
planting material. Many began using higher-yielding varieties with
resistance to cassava mosaic disease, as well as improved practices,
such as avoiding cultivation on wet soils and planting stakes along the
contours of sloping land in order to limit damage from root rot. They
also learned the importance of regular weeding, eliminating diseased
plants, planting in rows and optimizing planting densities.
An evaluation in 2012 found that, thanks mainly to the use of
high-yielding varieties, integrated pest management and resourceconserving cultivation practices, the farmers had increased their
cassava yields threefold. In one province, yields reached 30 tonnes
per hectare8.
Annex Tables 109
Annex tables
Chapter 1: Cassava, a 21st century crop
Table 1.1 Harvested area of cassava (million ha)
Sub-Saharan Africa
Asia
Latin America/Caribbean
1980
1990
2000
2011
7.05
8.59
11.01
13.05
3.893.853.40 3.91
2.65
2.75
2.54
2.67
Source: FAO. 2013. FAOSTAT statistical data
base (http://faostat.fao.org)
1980
1990
2000
2011
48.34
70.26
95.34
140.97
45.9449.79 49.46 76.68
29.70
32.21
31.30
34.36
Source: FAO. 2013. FAOSTAT statistical data
base (http://faostat.fao.org)
1980
1990
2000
2011
6.85
8.18
8.66
10.80
11.82 12.92 14.5319.60
11.23
11.72
12.34
12.88
Source: FAO. 2013. FAOSTAT statistical data
base (http://faostat.fao.org)
Table 1.2 Cassava production (million tonnes)
Sub-Saharan Africa
Asia
Latin America/Caribbean
Table 1.3 Average cassava yields (tonnes/ha)
Sub-Saharan Africa
Asia
Latin America/Caribbean
110 Save and Grow: Cassava
Chapter 2: Farming systems
Table 2.1 Effect of method of land preparation on the yield of two cassava varieties
in Mondomito, Cauca, Colombia in 1981/82
Cassava root yield (t/ha)
CMC 92
MCol 113
10.8
10.4
17.9
12.3
16
11.6
15
10
15.7
14.1
16.8
10.9
Tillage treatment
Without preparation
Hand preparation of planting holes
Preparation with oxen-drawn plough
Oxen-drawn plough followed by ridging Preparation with tractor-mounted rototiller
Rototilling followed by ridging
1 m wide strips prepared with hoe,
alternated with 1 m wide unprepared strips
Source: Howeler, R.H., Ezumah, H.C. &
Midmore, D.J. 1993. Tillage systems for root
and tuber crops in the tropics. Soil Tillage
Res., 27: 211-240.
12.29.7
1 m wide strips prepared with rototiller,
alternated with 1 m wide unprepared strips
LSD 5%
13.59.5
4
1.8
Table 2.2 Effect of tillage system and nitrogen application rate in the first year on cassava
root yield, Khon Kaen, Thailand, 2000/01 (tonnes/ha)
Source: Adapted from Jongruaysup, S.,
Treloges, V. & Chuenrung, C. 2003. Minimum
tillage for cassava production in Khon Kaen
Province, Thailand. Songklanakarin J. Sci.
Technol., 25(2): 191-197.
Tillage system
Fertilizer rate*
Conventional tillage
No tillage
0-50-50
42.755.13
50-50-50
44.9456.06
100-50-50
53.6967
Average
47.1359.38
* N-P2O5-K 2O in kg/ha
Table 2.3 Average responses of cassava top biomass, yield and root dry matter content
(8 years) on dry weight basis to surface plant mulch, fertilizer and tillage in sandy loam
soils, northern Colombia
Fertilization
Source: Adapted from Cadavid, L.F.,
El-Sharkawy, M.A., Acosta, A. & Sánchez,
T. 1998. Long-term effects of mulch,
fertilization and tillage on cassava grown in
sandy soils in northern Colombia. Field Crops
Res., 57: 45-56.
Treatment*
CT
CT+mulch
NT
NT+mulch
Mean
Root
yield
(t/ha)
Top
biomass
(t/ha)
5.51
5.92
4.42
6.11
5.49
* CT = conventional tillage; NT = no tillage
No fertilization
Root
dry
matter
(%)
3.1830.2
3.98 30.9
2.77 29.5
3.85 31
3.4530.4
Root
yield
(t/ha)
Top
biomass
(t/ha)
Root
dry
matter
(%)
2.19 1.4330.1
4.66 2.9330.6
1.93 1.4329.2
4.66 2.9530.4
3.36 2.1930.1
Annex Tables 111
Table 2.4 Effect of mulching on dry storage yield of late season cassava,
Democratic Republic of the Congo (t/ha)
1981-82
Mulch*
No mulch
Cultivar
Mpelolongi4.7 4
30085/28 5.3 4.4
2864
4.8 4.2
30122/2 3.7 3.6
30555/3 3.7 3.2
30010/10 3.4 3.7
Means 4.3 3.8
1982-83
Mulch*
1983-84
No mulch
Mulch*
6.2 4.7
6.7 5
7.1 5.2
4.5 3.9
5.2 3.7
4 3.1
5.6 4.3
No mulch
6.1 3.4
6.84.7
6.84.5
4.73.1
4.93.2
4.42.8
5.63.6
Source: Adapted from Lutaladio, N., Wahua,
T. & Hahn, S. 1992. Effects of mulch on soil
properties and on the performance of late
season cassava (Manihot esculenta Crantz)
on an acid ultisol in southwestern Zaire.
Tropicultura, 10(1): 20-26.
* Rice straw at 5 t/ha
Table 2.5 Average results of three FPR intercropping trials conducted by farmers
in Suoi Rao and Son Binh villages, Chau Duc district, Ba Ria-Vung Tau, Viet Nam in 2001/02
Treatment
C + groundnut intercrop
C + mungbean intercrop
C + soybean intercrop
C + maize intercrop
Cassava monoculture
Cassava
yield
(t/ha)
Starch
InterGross Production Net
Farmers’ Source: Adapted from Nguyen, H.H., Tran,
content crop yield income
income preference T.D., Nguyen, T.S., Tran, C.K., Tuan, V.V. &
costs
Tong, Q.A. 2008. The FPR cassava project
(%)
(t/ha)
(%)
30.74
29.81
34.54
21
21.00
31.88
27.66
26.66
27.5
24.3
24.30
27.93
1.483
0.57
0
3.643
3.64
-
(million dong/ha)
25.81
10.07
15.73
20.38
8.64
11.74
19.00
8.62 10.38
15.56
8.59
6.90
17.53
7.12 10.42
48
42
6
35
29
and its impact in South Viet Nam. In R.H.
Howeler, ed. Integrated cassava-based
cropping systems in Asia. Working with
farmers to enhance adoption of more
sustainable production practices. Proceedings
of a Workshop on the Nippon Foundation
Cassava Project in Thailand, Viet Nam and
China, held in Thai Nguyen, Viet Nam. Oct.
27-31, 2003. pp. 140-156.
Table 2.6 Effect of various crop management treatments on soil loss due to erosion and
the yield of cassava and intercropped groundnut, as well as the gross and net income in an
FPR erosion control trial conducted by six farmers in Kieu Tung village of Thanh Ba district,
Phu Tho province, Viet Nam in 1997 (3rd year)
Dry soil
loss (t/ha)
Treatment*
C monoculture with fertilizer, no hedgerows 106.1
C+G, no fertilizer, no hedgerows
103.9
C+G, with fertilizer, no hedgerows
64.8
C+G, with fertilizer, Tephrosia hedgerows
40.1
C+G, with fertilizer, pineapple hedgerows
32.2
C+G, with fertilizer, vetiver hedgerows
32
C monocult., with fertilizer, Tephrosia hedgerows 32.5
Yield (t/ha)
Cassava
Groundnut
19.17
13.08
0.7
19.23
0.97
14.67
0.85
19.39
0.97
23.71
0.85
23.33
-
* C = cassava; G = groundnut; fertilizers = 60 kg N + 40 P2O5 + 120 K 2O/ha; all plots received 10 t/ha pig manure
Source: Adapted from Howeler, R.H. 2001. The
use of farmer participatory research (FPR) in
the Nippon Foundation Project: Improving
the sustainability of cassava-based cropping
systems in Asia. In R.H. Howeler & S.L. Tan,
eds. Cassava’s potential in Asia in the 21st
Century: Present situation and future research
and development needs. Proc. 6th Regional
Workshop, held in Ho Chi Minh city, Viet
Nam. Feb. 21-25, 2000. pp. 461-489.
112 Save and Grow: Cassava
Source: Adapted from Tamil Nadu
Agricultural University (TNAU). 2002. Report
to Quinquennial Review Team – Tuber crops
(1997-98 to 2001-02). Coimbatore Centre,
AICRP on tuber crops (other than potato).
Dept. of Vegetable Crops, Horticultural
College and Research Institute, TNAU
Coimbatore. pp. 34-35.
Table 2.7 Economics of sequential cropping with cassava and vegetable cowpea,
Tamil Nadu, India
Treatment*
No treatment
Half treatment
Full treatment
Cassava root
yield (t/ha)
26.9
41.2
40.9
Production
cost (‘000 Rs/ha)
16.04
19.60
24.94
Gross income
(‘000 Rs/ha)
56.24
80.90
80.73
Net returns
(‘000 Rs/ha)
40.19
61.30
55.79
* Full treatment = 26 kg/ha P + 25 tonnes/ha farmyard manure
Chapter 3: Varieties and planting material
Table 3.1 Major collections of cassava germplasm
Source: Adapted from FAO. 2010. The second
report on the state of the world’s plant genetic
resources for food and agriculture. Rome.
Type of accession* (%)
Number
of
Location
WS
LR
BL
AC
OT
accessions
CIAT
5436 187 11 0 1
Brazil 2889 0 0 0 0100
IITA
2756 028 47 0 25
India 1327 0 0 0 0100
Nigeria 1174 0 0 0 0100
Uganda 1136 0 489 7 0
Malawi 978 022 72 6 0
Indonesia 954 0 0 0100 0
Thailand 609 0 0100 0 0
Benin
600 0100 0 0 0
Togo
435 0100 0 0 0
Other 14148 626 3 14 51
* WS = wild species; LR = landraces/old cultivars; BL = research materials/breeding lines; AC = advanced cultivars;
OT = others (type unknown or a mixture of two or more types)
Table 3.2 Effect of N, P and K fertilization of mother plants of cassava used for production
of planting material on the root and stem yield of the subsequent crop
Source: Adapted from Lopez, J. & ElSharkawy, M.A. 1995. Increasing crop
productivity in cassava by fertilizing
production of planting material. Field Crops
Res., 44: 151-157.
Fertilization
of mother
Sprouting
plants
(%)
(kg/ha)*
N P K
0 0 0
85
0 100 100
97
100 0 100
98
100 100 0
77
100 100 100
97
Roots
13.5
17.5
14.9
15.8
24.2
Fresh root and stem yields (t/ha)
Unfertilized
Fertilized**
Stems
Roots
Stems
2.02
19.1
4.49
2.63
25.6
3.64
2.98
23.5
4.38
2.25
24.7
4.53
3.10
30.2
6.22
* Rates are in kg/ha of N, P and K
** Application at planting of 50 kg N, 43 kg P and 83 kg K/ha
Annex Tables 113
Chapter 4: Water management
Table 4.1 Effect of delayed planting on root yield of late season cassava
in southern Nigeria
Month of planting
Root yield (dry
Percent of June
weight, t/ha)
planting yield
June 10.81100
July 9.7290
August6.91 64
September6.70
62
October4.48 41
Source: Adapted from International Institute
of Tropical Agriculture (IITA). 1977. Annual
Report for 1977. Ibadan, Nigeria.
Table 4.2 Effect of time of planting and age at harvest on yield (t/ha) in Thailand (1976-78)
8 months
10 months
12 months
14 months
16 months
18 months
Average
May 20.27 26.9836.4942.46 49.52 57.06 38.76
Jun 22.15 27.73 36.51 47.31 51.9353.3639.83
Jul 19.82 29.07 35.0740.7444.05 48.51 36.21
Aug 14.46 22.96 29.1438.62 39.5743.68 31.41
Sep 12.25 17.6428.6532.4834.5936.2626.98
Oct 8.1616.6922.1723.9529.5232.6122.18
Source: Adapted from Sinthuprama, S. 1980.
Cassava planting systems in Asia. In E.J.
Weber, J.C. Toro & M. Graham, eds. Cassava
cultural practices. Proc. of a Workshop, held
in Salvador, Bahia, Brazil. March 18-21, 1980.
pp. 50-53.
Table 4.3 Effect of different planting dates, and the average rainfall received, on cassava
growth and yield when cassava, cv. Rayong 90, was grown for three consecutive cycles at
Rayong Field Crops Research Center in Thailand from 1994 to 1998
Month of
planting*
Total
rainfall**
(mm)
Canopy
cover***
(%)
June
1402
August 1409
October 1267
December 1665
February 1633
April
1616
Final
plant stand
(%)
77.3
55.0
55.0
82.0
89.2
87.8
97
97
91
90
88
87
* Roots were harvested after 11 months
** Rainfall received during the 11-month growth cycle
*** Percent canopy cover averaged over all months of the growth cycle
Root
yield
(t/ha)
Starch
content
(%)
Starch
yield
(t/ha)
23.3221.27 4.96
18.9222.33 4.22
24.5625.73 6.32
32.1825.07 8.07
27.9230.35 8.47
25.6726.13 6.71
Source: Adapted from Howeler, R.H. 2001.
Cassava agronomy research in Asia: Has it
benefited cassava farmers? In R.H. Howeler
& S.L. Tan, eds. Cassava’s potential in Asia in
the 21st Century: Present situation and future
research and development needs. Proc. 6th
regional workshop, held in Ho Chi Minh city,
Viet Nam. Feb 21-25, 2000. pp. 345-382.
114 Save and Grow: Cassava
Table 4.4 Effect of planting method, stake position, stake length, and planting depth
on cassava yield, planted in both the rainy and dry season at Rayong Field Crops Research
Center, Thailand
Rainy season (May-August)
No.
plants
survived
(‘000/ha)*
Root
yield
(t/ha)
Starch
content
(%)
No.
plants
survived
(‘000/ha)*
Root
yield
(t/ha)
Starch
content
(%)
14.57
14.43
14.98
13.47
16.64
16.66
10.69
12.09
14.69
14.96
18.63
18.65
Stake position Vertical
Stake position Inclined
Stake position Horizontal
14.87
14.89
13.74
16.04
15.46
11.08
17.03
17.14
15.85
13.04
11.99
9.31
17.74 16.40
10.32
19.04
18.68
18.17
Stake length (20 cm)
Stake length (25 cm)
14.55
14.41
14.52
13.54
16.67
16.69
10.58
13.02
14.53
15.41
18.51
18.87
Planting depth (5-10 cm)
Planting depth (15 cm)
14.43
14.56
13.90
14.43
16.61
16.73
9.74
12.71
13.14
16.17
18.21
18.97
Treatment
Planting method Ridge
Planting method No ridge
Source: Adapted from Tongglum, A.,
Vichukit, V., Jantawat, S., Sittibusaya, C.,
Tiraporn, C., Sinthuprama, S. & Howeler, R.H.
1992. Recent progress in cassava agronomy
research in Thailand. In R.H. Howeler, ed.
Cassava breeding, agronomy and utilization
research in Asia. Proc. 3rd regional workshop,
held in Malang, Indonesia. Oct. 22-27, 1990.
pp. 199-223.
Early dry season (November)
Data are the average of three years, 1987-1989
* Out of a total of 15 625 stakes/ha planted
Table 4.5 Effect of supplemental flood irrigation on the average root yield, and starch
and HCN contents of cassava planted at CTCRI, Trivandrum, India, 1982-1985
Source: Adapted from Nayar, T.V.R.,
Mohankumar, B. & Pillai, N.G. 1985.
Productivity of cassava under rainfed and
irrigated conditions. J. Root Crops, 11(1-2):
37-44.
Level of irrigation*
IW/CPE = 0 (rainfed)
IW/CPE = 0.25
IW/CPE = 0.50
IW/CPE = 0.75
IW/CPE = 1.0
C.D. (0.05)
Fresh root yield
(t/ha)
Starch content
(% on dry wt. basis)
20.8
24.5
30.8
34.8
39.7
4.8
72.7
72.9
74.5
75.2
75
HCN
(ppm on fresh
wt. basis)
55
41
41
33
22
* Irrigation during drought periods (more than 7 days without rains); IW = irrigation water in mm; CPE = cumulative pan
evaporation in mm.
Table 4.6 Effect of flood and drip irrigation on the fresh root yield of cassava grown for
three consecutive years on sandy loam soils in Bhavanisagar, Tamil Nadu, India (t/ha)
Source: Adapted from Manickasundaram,
P., Selvaraj, P.K., Krishnamoorthi, V.V. &
Gnanamurthy, P. 2002. Drip irrigation and
fertilization studies in tapioca. Madras Agric.
J., 89(7-9): 466-468.
Irrigation method/level*
Flood irrigation, 5 cm at 0.60 IW/CPE
Drip irrigation at 100% of flood irrigation
Drip irrigation at 75% of flood irrigation
Drip irrigation at 50% of flood irrigation
1996/1907
48.5
57.6
53.9
51.6
* IW = irrigation water in mm; CPE = cumulative pan evaporation in mm.
1998
59.8
67.3
64.6
62.2
1999/2000
45.8
51.2
50.4
46.2
Annex Tables 115
Table 4.7 Effect of different amounts of supplemental drip irrigation on the tuber yield of
cassava grown for two years at the Federal University of Technology in Akure, Nigeria
Level of drip
irrigation (% of
available soil water)
Dry root yield
Total water supplied by
(t/ha)*
irrigation as % of water used
2006/07
2007/08
2006/07
2007/08
4.662.98 0 0
8.53 6.4314.83 17.85
13.10 9.20 34.33 40.65
28.15 15.3651.11 61.72
0
25
50
100
Source: Adapted from Odubanjo, O.O.,
Olufayo, A.A. & Oguntunde, P.G. 2011. Water
use, growth, and yield of drip irrigated
cassava in a humid tropical environment. Soil
Water Res., 6(1): 10-20.
* For a 9-month growth cycle, during which period total rainfall was 872 and 795 mm in 2006/07 and 2007/08, respectively
Chapter 5: Crop nutrition
Table 5.1 Nutrient distribution in 12-month-old cassava, cv. M Ven 77, grown without
fertilization in Carimagua, Colombia (kg/ha)
N
Roots
30.3
Plant tops
69.1
Fallen leaves 23.7
P
K
Ca Mg
7.5 54.9 5.4 6.5
7.4 33.6 37.4 16.2
1.5
4 24.7
4
S
B
Cu
Fe Mn Zn
3.3 0.080.02 0.380.02 0.1
8.2 0.07 0.03 0.45 0.33 0.26
2.5 0.04 0.01
0 0.37 0.18
Source: Adapted from Howeler, R.H. 1985.
Mineral nutrition and fertilization of
cassava. In J.H. Cock & J.A. Reyes, eds.
Cassava: Research, production and utilization.
UNDP-CIAT Cassava Program. Cali, Colombia.
pp. 249-320.
Table 5.2 Effect of four sources of nitrogen on the yield and quality attributes of cassava,
cv. Sree Visakham, grown at the College of Agriculture, Trivandrum, India, 1989-1991
Number
of roots/plant
Urea
Neem-coated urea
Urea super-granule
Rubber cake-coated urea
Root yield
(t/ha)
HCN content
Total dry
(ppm, fresh
matter
weight basis)
(t/ha)
5.119.95 47.410.52
5.8
22.59
46.8
12.13
5.9
25.65
48.4
13.97
4.9
17.76
48.2
10.4
Source: Vinod, G.S. & Nair, V.M. 1992. Effect
of slow release nitrogenous fertilizers on the
growth and yield of cassava. J. Root Crops
(Special issue), 17: 123-125.
116 Save and Grow: Cassava
Table 5.3 Effect of planting intercrops, green manures and alley crops, with or without
fertilizers, on cassava and intercrop yields, as well as the gross and net income obtained
when cassava, KM 60, was grown for the 16th consecutive year at Hung Loc Agricultural
Research Center in Dongnai, Viet Nam in 2007/08
Root yield
(t/ha)
with
Source: Nguyen Huu Hy, personal
communication.
without
Starch content
(%)
with
without
Gross
Production
Net
income
costs
income
(million d/ha) (million d/ha) (million d/ha)
with
without
with
without
with
without
fertilizer fertilizer fertilizer fertilizer fertilizer fertilizer fertilizer fertilizer fertilizer fertilizer
Treatment*
C monoculture 17.44 4.81 23.28 21.28 20.41 5.63 6.01 3.80 14.40 1.83
C+pigeon pea GM 15.62 6.75 23.6 21.7 18.28 7.90 8.11 5.90 10.17 2.00
C+Mucuna GM 17.82 8.56 24.45 22.35 20.85 10.02 8.11 5.90 12.74 4.12
C+groundnut IC 20.41 8.62 25.35 24.08 24.82 10.09 8.11 5.90 16.72 4.19
C+cowpea IC
19.44 7.44 24.92 22.65 22.75 8.71 8.11 5.90 14.64 2.81
C+Crotalaria GM 18.75 8.5 24.95 21.72 21.94 9.95 8.11 5.90 13.83 4.05
C+Leucaena AC 20.68 13.39 25.52 24.4 24.20 15.67 7.71 5.50 16.49 10.17
C+Gliricidia AC 19.316.75 26.32 24.95 22.58 19.60 7.71 5.50 14.87 14.10
Average
18.68 9.35 24.822.89 21.98 10.94 7.75 5.54 14.23 5.40
* C = cassava; GM = green manure;
IC = intercrop; AC = alley crop
Table 5.4 Effect of application of various rates of chemical fertilizer and incorporation
of the green manure species Tithonia diversifolia and Chromolaena odorata on cassava fresh
root yields (t/ha) during two cropping cycles at two sites in the Bas-Congo region
of DR Congo
Source: Adapted from Pypers, P.,
Sanginga, J.M., Kasereka, B., Walangululu,
M. & Vanlauwe, B. 2011. Increased
productivity through integrated soil
fertility management in cassava-legume
intercropping systems in the highlands of
Sud-Kivu, DR Congo. Field Crops Res., 120:
76-85.
Green manures
None
None
None
None
Tithonia
Tithonia
Tithonia
Chromolaena
Chromolaena
Chromolaena
* Fertilizer = 17-17-17 as N-P2O5- K 2O
Fertilizer rate*
(kg/ha)
0
283
850
1,417
0
283
850
0
283
850
First crop
Second crop
Kiduma Mbuela
Kiduma Mbuela
12.710.5 10.1 5.4
23.714.9 14.9 7.4
31.419.6 17.6 9
39.618.6 33.1 18
32.818.1 12.76.4
37.623.5 17.8 8.7
41.521.7 20.28.2
19.918.2 12.2 7.3
29.521.1 18.48.5
35.223.4 18.6 9
Annex Tables 117
Table 5.5 Effect of the application of farm-yard manure (FYM) and chemical fertilizers
on cassava yield and economic benefit at Thai Nguyen University of Agriculture and
Forestry in Thai Nguyen province of Viet Nam, in 2001 (2nd year)
Cassava Harvest
root yield Index
(t/ha)
Treatment
No fertilizers, no FYM
3.25
5 t FYM/ha
7.79
10 t FYM/ha
10.02
15 t FYM/ha
13.11
80 N+80 K2O/ha, no FYM 15.47
80 N+80 K2O/ha + 5 t FYM/ha17.98
80 N+80 K2O/ha + 10 t FYM/ha18.7
80 N+80 K2O/ha + 15 t FYM/ha18.5
Gross
income
0.39
0.49
0.52
0.52
0.5
0.48
0.49
0.48
Net
Fertilizer Production
income
costs
costs
(‘000 dong/ha)
1,625
0
2,800
-1,175
3,895
500
3,300
595
5,010
1,000
3,800
1,210
6,555
1,500
4,300
2,255
7,735
680
3,580
4,155
8,990 1,180 4,080 4,910
9,350 1,680 4,580 4,770
9,250 2,180 5,080 4,170
Source: Adapted from Nguyen The Dang,
personal communication, 2002.
Table 5.6 Effect of various fertilizer combinations on the fresh root yields of cassava, cv.
Faroka, and on the grain yield of intercropped maize, as well as gross and net income when
grown in Jatikerto Station in Malang, East Java, Indonesia, in 2005/06 (2nd year)
Treatment
N-P2O5-K2O
(kg/ha)
Organic
(t/ha)
0-0-0 0
135-0-0 0
135-50-00
135-50-1000
0-0-0
10 manure
0-0-0
10 compost
135-0-0
5 manure
135-0-0
5 compost
135-50-0 5 compost
135-0-0
5 sugar mud
Cassava
yield
(t/ha)
Maize
yield
(t/ha)
Gross
income
Fertilizer Production
Net
Farmers’
costs
costs
income preference
(mil. Rp/ha)
10.96 1.1 4.72 0 4.10.62 35.61.93 13.520.45 7.01 6.51 2
36.82.07 14.05 0.69 7.37 6.68 3
37.47 2.1 14.3 1.27 8.02 6.28 4
26.53 1.66
10.32
2
7.65
2.67
22.67 1.63
9.05
1
6.27
2.78
35.63 2.26
13.89
1.45
8.01
5.88
1
39.33 1.97
14.75 0.95
7.88
6.87
5
39.07 1.87
14.56
1.19
8.1
6.46
33.73 1.67
12.63 0.95
7.32
5.31
Source: Adapted from Utomo, W.H., Marjuki,
W., Hartoyo, K., Suharjo Retnaningtyas, E.,
Santoso, D. & Wijaya, A. 2010. Enhancing the
adoption of improved cassava production
and utilization systems in Indonesia (The
ACIAR Cassava Project in Indonesia). In R.H.
Howeler, ed. A new future for cassava in Asia:
Its use as food, feed and fuel to benefit the
poor. Proc. 8th Regional Workshop, held in
Vientiane, Lao PDR. Oct. 20-24, 2008. pp.
490-507.
Table 5.7 Average nutrient content of one tonne of various types of wet manure and
compost as compared to 50 kg of 15-15-15 chemical fertilizers
1 t cattle manure
1 t pig manure
1 t chicken manure
1 t sheep manure
1 t city garbage compost
50 kg 15-15-15 fertilizer
DM (%)
32
40
57
35
71
100
N (kg)
5.9
8.2
16.6
10.5
6.9
7.5
P (kg)
2.6
5.5
7.8
2.2
3.3
3.3
K (kg)
5.4
5.5
8.8
9.4
6.1
6.2
Source: Howeler, R.H. 2001. Cassava
agronomy research in Asia: Has it benefited
cassava farmers? In R.H. Howeler & S.L. Tan,
eds. Cassava’s potential in Asia in the 21st
Century: Present situation and future research
and development needs. Proc. 6th regional
workshop, held in Ho Chi Minh city, Viet
Nam. Feb. 21-25, 2000. pp. 345-382.
118 Save and Grow: Cassava
Table 5.8 Effect of various soil conservation practices on the average relative cassava yield
and dry soil loss due to erosion as determined from soil erosion control experiments, FPR
demonstration plots and FPR trials conducted in Viet Nam from 1993 to 2003
Relative
cassava yield (%)
Source: Adapted from Howeler, R.H. 2008.
Results, achievements and impact of
the Nippon Foundation Cassava Project.
In R.H. Howeler, ed. Integrated cassavabased cropping systems in Asia. Working
with farmers to enhance adoption of more
sustainable production practices. Proc. of
a Workshop on the Nippon Foundation
Cassava Project in Thailand, Viet Nam and
China, held in Thai Nguyen, Viet Nam, Oct.
27-31, 2003. pp. 161-209.
Soil conservation practice
With fertilizers; no hedgerows (check)
With fertilizers; vetiver grass hedgerows
With fertilizers; Tephrosia candida hedgerows
With fertilizers; Flemingia macrophylla hedgerows
With fertilizers; Paspalum atratum hedgerows
With fertilizers; Leucaena leucocephala hedgerows
With fertilizers; Gliricidia sepium hedgerows
With fertilizers; pineapple hedgerows
With fertilizers; vetiver + Tephrosia hedgerows
With fertilizers; contour ridging; no hedgerows With fertilizers; closer spacing, no hedgerows
With fertilizers; groundnut intercrop; no hedgerows
With fertilizers; maize intercrop; no hedgerows
No fertilizers; no hedgerows
Relative dry
soil loss (%)
Cassava
Cassava
Cassava
Cassava
mono­culture + groundnut mono­culture + groundnut
100
113
110
103
112
110
107
100
-
106
122
106
69
32
-
115
105
109
-
-
-
103
102
-
-
100
-
92
100
48
49
51
50
69
71
48
-
70
103
81
21
137
51
64
62
44
62
100
202
Chapter 6: Pests and diseases
Table 6.1 Effect of hand weeding at different times and frequencies on the fresh root yield
of cassava, cv. CMC 39, at 280 days after planting at CIAT, Cali, Colombia
Source: Doll, J.D. & Piedrahita, C.W. 1978.
Methods of weed control. Cali, Colombia, CIAT.
No.
of hand
weedings*
4 +
3 +
2+
1+
Frequency of hand weeding
(days)
15
30
30
Fresh
Yield as %
cassava root of maximum
yield (t/ha)
yield***
60
120
UH**
18.0
86
60
120
UH
16.0
76
60 120 UH
11.0
52
120 UH
7.0
33
4
3
2
1
15
15
15
15
30
30
30
60 120 60 19.5
12.9
13.3
5.8
92
61
63
28
2
2
0
0
15
30 60 45
Chemical weed check
Weedy check
16.3
15.4
21.1
1.4
77
73
100
7
* + = additional weedings
** UH = until harvest, as needed
*** Percentage of the yield of cassava weeded with herbicides
Annex Tables 119
Chapter 7: Harvest, post-harvest and value addition
Table 7.1 Average effect of the number and timing of leaf cutting on the total dry leaf and
protein yields, root yield and starch content of two cassava varieties, as well as gross and
net income obtained in an experiment at TTDI Center in Huay Bong, Thailand
No. of leaf cuts*
Total Pro- Total Fresh Root
Gross income
dry
tein
leaf
root starch
leaf content protein yield content Leaves Roots Total
yield
(%)
yield (t/ha) (%)
(t/ha)
(t/ha)
Production costs
Net
income
1
2
3
4
5 (‘000 B/ha)
x 0.7124.46 0.1739.8919.58 4.1545.4349.58 24.3 25.28
x x 1.5 25.16 0.38 39.9120.15 9.02 46.01 55.04 30.68 24.35
xx x 1.99 25.21 0.5 27.02 21.1 11.92 31.59 43.51 32.53 10.99
xx x x 2.56 25.13 0.64 28.6 19.75 15.34 32.53 47.88 36.78 11.09
xx x xx 2.57 25.28 0.65 24.46 18.19 15.56 27.2 42.76 40.07
2.7
Average 1.87 25.05 0.47 31.97 19.75 11.2 36.55 47.75 32.87 14.88
Source: Adapted from Howeler, R.H. 2012.
Cassava leaf production for animal feeding.
In R.H. Howeler, ed. The cassava handbook
– A reference manual based on the Asian
regional cassava training course, held in
Thailand. Cali, Colombia, CIAT. pp. 626-648.
* Cuts no. 1, 2, 3, 4 and 5 correspond to leaf cuttings at 2.5, 5, 7, 9 and 11 MAP, respectively, with the last cut at time of root
harvest
Chapter 8: The way forward
Table 8.1 Effect of various crop management treatments on soil loss due to erosion and
the yield of cassava and intercropped groundnut, as well as the gross and net income in an
FPR erosion control trial conducted by six farmers in Kieu Tung village of Thanh Ba district,
Phu Tho province, Viet Nam in 1997 (3rd year)
Treatment*
C monoculture with fertilizer, no hedgerows
C+G, no fertilizer, no hedgerows
C+G, with fertilizer, no hedgerows
C+G, with fertilizer, Tephrosia hedgerows C+G, with fertilizer, pineapple hedgerows
C+G, with fertilizer, vetiver hedgerows
C monocult. with fertilizer, Tephrosia hedgerows
Gross
income
9.58
10.04
14.47
11.58
14.55
16.1
11.66
ProducNet
tion costs income
(mil. dong/ha)
3.72
5.86
5.13
4.91
5.95
8.52
5.95
5.63
5.95
8.6
5.95
10.15
4.54
7.12
Farmers’
ranking
* C = cassava; G = groundnuts; fertilizers = 60 kg N + 40 P2O5 + 120 K 2O/ha; all plots received 10 t/ha pig manure
6
5
3
2
1
4
Source: Adapted from Howeler, R.H. 2001. The
use of farmer participatory research (FPR) in
the Nippon Foundation Project: Improving
the sustainability of cassava-based cropping
systems in Asia. In R.H. Howeler & S.L. Tan,
eds. Cassava’s potential in Asia in the 21st
Century: Present situation and future research
and development needs. Proc. 6th Regional
Workshop, held in Ho Chi Minh city, Viet
Nam. Feb. 21-25, 2000. pp. 461-489.
References 121
References
Chapter 1: Cassava, a 21st
century crop
1. Allem, A.C. 2002. The origins and
taxonomy of cassava. In R.J. Hillocks, J.
M. Thresh & A.C. Bellotti, eds. Cassava:
Biology, production and utilization.
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planting material: standards and
protocols for vegetatively planting
material. Rome.
20. Chakrabarti, S.K. 2012. Solutions
in sight to control the cassava mosaic
disease in India. Factsheet prepared for
FAO. (mimeo)
21. CTA. 2012. Cassava stem
multiplication technology: A viable
option for industry development?, by
E.K. Chikwado. Umudike, Nigeria,
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23. ASARECA & TUUSI. 2007.
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and tuber improvement programme
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Lakes cassava initiative, by S. Walsh.
Baltimore, USA.
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IPM field guide for extension agents,
by B. James, J. Yaninek, A. Tumanteh,
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Kwarteng, eds. Lagos, Nigeria.
27. Lopez, J. & El-Sharkawy, M.A. 1995.
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Chapter 4: Water
management
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Report 2006. Beyond scarcity: Power,
poverty and the global water crisis. New
York, USA.
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for life. A comprehensive assessment of
water management in agriculture, by
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London, Earthscan.
3. Hershey, C., Álvarez, E., Aye, T.M.,
Becerra, L.A., Bellotti, A., Ceballos,
H., Fahrney, K., Howeler, R., Lefroy,
R., Ospina, B. & Parsa, S. 2012. Ecoefficient interventions to support
cassava’s multiple roles in improving
the lives of smallholders. In CIAT. Ecoefficiency: From vision to reality. Cali,
Colombia.
4. El-Sharkawy, M.A. 1993. Droughttolerant cassava for Africa, Asia and
Latin America. Bioscience, 43: 441-451.
5. Agili, S.M. & Pardales Jr., J.R. 1997.
Influence of moisture and allelopathic
regimes in the soil on the development
of cassava and mycorrhizal infection of
its roots during establishment period.
Philippine Journal of Crop Science, 1997
22(2): 99-105.
6. Pardales Jr., J.R., & Esquibel, C.B.
1996. Effect of drought during the
establishment period on the root
system development of cassava. Jpn. J.
Crop Sci., 65(1): 93-97.
7. Pardales Jr., J.R., Yamauchi, A.,
Belmonte Jr, D.V. & Esquibel, C.B.
2001. Dynamics of root development in
root crops in relation to the prevailing
moisture stress in the soil. Proceedings
of the 6th Symposium of the
International Society of Root Research,
Nagoya, Japan, November. pp. 72-73.
8. Howeler, R.H. 2001. Cassava
agronomy research in Asia: Has it
benefited cassava farmers? In R.H.
Howeler & S.L. Tan, eds. Cassava’s
potential in Asia in the 21st Century:
Present situation and future research
and development needs. Proc. 6th
regional workshop, held in Ho Chi
Minh city, Viet Nam. Feb. 21-25, 2000.
pp. 345-382.
9. Odubanjo, O.O., Olufayo, A.A.
& Oguntunde, P.G. 2011. Water
use, growth, and yield of drip
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Chapter 5: Crop nutrition
1. FAO. 2012. Save and Grow. A
policymaker’s guide to the sustainable
intensification of smallholder crop
production. Rome.
10. Putthacharoen, S., Howeler, R.H.,
Jantawat, S. & Vichukit, V. 1998.
Nutrient uptake and soil erosion losses
in cassava and six other crops in a
Psamment in eastern Thailand. Field
Crops Res., 57(1): 113-126.
2. Howeler, R.H. 2012. Importance of
mycorrhiza for phosphorus absorption
by cassava. In R.H. Howeler, ed. The
Cassava Handbook – A reference
manual based on the Asian regional
cassava training course, held in
Thailand. Cali, Colombia, CIAT.
pp. 497-523.
11. FAO. 1980. Review of data on
responses of tropical crops to fertilizers,
1961-1977, by I.R. Richards. Rome.
3. Howeler, R.H., Sieverding, E. & Saif,
S. 1987. Practical aspects of mycorrhizal
technology in some tropical crops
and pastures. Plant & Soil, 100(1-3):
249-283.
13. IFAD. 2012. Global consultation on
cassava as a potential bioenergy crop, by
E. Kueneman, V. Raswant, N. Lutaladio
& R. Cooke. Accra.
4. Howeler, R.H. 1985. Mineral
nutrition and fertilization of cassava. In
J.H. Cock & J.A. Reyes, eds. Cassava:
Research, production and utilization.
UNDP-CIAT Cassava Program. Cali,
Colombia. pp. 249-320.
5. Howeler, R.H. 1991. Long-term
effect of cassava cultivation on soil
productivity. Field Crops Res., 26: 1-18.
6. Howeler, R.H. 2002. Cassava mineral
nutrition and fertilization. In R.J.
Hillocks, M.J. Thresh & A.C. Bellotti,
eds. Cassava: Biology, production and
utilization. Wallingford, UK, CAB
International. pp. 115-147.
7. Howeler, R.H. 1981. Mineral nutrition
and fertilization of cassava. CIAT Series
09-EC-4. Cali, Colombia, CIAT.
8. Howeler, R.H. 2001. Cassava
agronomy research in Asia: Has it
benefited cassava farmers? In R.H.
Howeler & S.L. Tan, eds. Cassava’s
potential in Asia in the 21st Century:
Present situation and future research
and development needs. Proc. 6th
regional workshop, held in Ho Chi
Minh city, Viet Nam. Feb. 21-25, 2000.
pp. 345-382.
9. Howeler, R.H. 2012. Effect of cassava
production on soil fertility and the longterm fertilizer requirements to maintain
high yields. In R.H. Howeler, ed. The
cassava handbook – A reference manual
based on the Asian regional cassava
training course, held in Thailand. Cali,
Colombia, CIAT. pp. 411-428.
12. Vanlauwe, B. 2012. Integrated soil
fertility management for increased
productivity in cassava-based systems.
Factsheet prepared for FAO. (mimeo)
14. Vinod, G.S. & Nair, V.M. 1992.
Effect of slow release nitrogenous
fertilizers on the growth and yield of
cassava. J. Root Crops (Special issue), 17:
123-125.
15. Nayar, T.V.R., Suja, G., Susan John,
K. & Ravi, V. 2007. Cassava agronomy
in India – Low input management.
In CIAT. Cassava research and
development in Asia: Exploring new
opportunities for an ancient crop, by
R.H. Howeler, ed. Proc. 7th regional
workshop, Bangkok, Thailand. Oct. 28Nov. 1, 2002. Bangkok. pp. 183-203.
16. Hauser, S. 2012. Natural resource
management in cassava and yam
production systems. In IITA. R4D
Review 9:35-39. B. Vanlauwe & K.
Lopez, eds. Ibadan, Nigeria.
17. Makinde, E.A., Saka, J.O. &
Makinde, J.O. 2007. Economic
evaluation of soil fertility management
options on cassava-based cropping
systems in the rain forest ecological
zone of South Western Nigeria. Afr. J.
Agric. Res., 2: 7-13.
18. Pypers, P., Sanginga, J.M., Kasereka,
B., Walangululu, M. & Vanlauwe, B.
2011. Increased productivity through
integrated soil fertility management in
cassava-legume intercropping systems
in the highlands of Sud-Kivu, DR
Congo. Field Crops Res., 120: 76-85.
19. Hauser, S., Nolte, C. & Carsky, R.J.
2006. What role can planted fallows
play in the humid and sub-humid zone
of West and Central Africa? Nutrient
Cycling in Agroecosystems, 76(2-3):
297-318.
20. Mutsaers, H.J.W., Ezuma, H.C.
& Osiru, D.S.O. 1993. Cassava-based
intercropping: A review. Field Crop
Res., 34: 431-457.
21. Howeler, R.H. 2012. Soil fertility
maintenance: Organic solutions. In R.H.
Howeler, ed. The cassava handbook – A
reference manual based on the Asian
regional cassava training course, held
in Thailand. Cali, Colombia, CIAT. pp.
469-496.
22. Cadavid, L.F., El-Sharkawy, M.A.,
Acosta, A. & Sanchez, T. 1998. Longterm effects of mulch, fertilization and
tillage on cassava grown in sandy soils
of northern Colombia. Field Crops Res.,
57: 45-56.
23. FAO. 2001. Conservation
agriculture. Case studies in Latin
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24. Pypers, P., Bimponda, W., LodiLama, J.P., Lele, B., Mulumba, R.,
Kachaka, C., Boeckx, P. & Vanlauwe, B.
2012. Combining mineral fertilizer and
green manure for increased, profitable
cassava production. Agron. J., 104: 1-10.
25. Howeler, R. 2001. Nutrient inputs
and losses in cassava-based cropping
systems – Examples from Viet Nam
and Thailand. International workshop
on nutrient balances for sustainable
agricultural production and natural
resource management in Southeast
Asia. Bangkok, Thailand, 20-22
February, 2001. Colombo, IWMI.
26. Müller-Sämann, K.M. & Leihner,
D.E. 1999. Soil degradation and crop
productivity research for conservation
technology development in Andean
hillside farming. Final report – GTZ
Project. Stuttgart, Germany, Institute
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Chapter 6: Pests and diseases
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intensification of smallholder crop
production. Rome.
2. Alvarez, E. 2010. Cassava diseases in
Latin America, Africa and Asia. In R.H.
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in Asia: Its use as food, feed and fuel
to benefit the poor. Proc. 8th regional
workshop, held in Vientiane, Lao PDR.
Oct. 20-24, 2008. pp. 590-629.
3. Alvarez, E., Llano, G.A. & Mejia,
J.F. 2012. Cassava diseases in Latin
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regional cassava training course, held
in Thailand. Cali, Colombia, CIAT. pp.
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4. Bellotti, A.C., Herrera, C.L.,
Hernandez, M.P., Arias, B., Guerrero,
J.M. & Melo, E.L. 2010. Three major
cassava pests in Latin America, Africa
and Asia. In R.H. Howeler, ed. A new
future for cassava in Asia: Its use as
food, feed and fuel to benefit the poor.
Proc. 8th regional workshop, held in
Vientiane, Lao PDR. Oct. 20-24, 2008.
pp. 544-577.
5. Bellotti, A.C., Herrera, C.L.,
Hernandez, M.P., Arias, B., Guerrero,
J.M. & Melo, E.L. 2012. Cassava Pests in
Latin America, Africa and Asia. In R.H.
Howeler, ed. The Cassava Handbook –
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regional cassava training course, held
in Thailand. Cali, Colombia, CIAT. pp.
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6. IITA. 2009. Laboratory manual for
the diagnosis of cassava virus diseases,
by P.L. Kumar & J.P. Legg, eds. Ibadan,
Nigeria.
7. Legg, J.P., Jeremiah, S.C., Obiero,
H.M., Maruthi, M.N., Ndyetabula,
I., Okao-Okuja, G., Bouwmeester,
H., Bigirimana, S., Tata-Hangy, W.,
Gashaka, G., Mkamilo, G., Alicai,
T. & Kumar, P.L. 2011. Comparing
the regional epidemiology of cassava
mosaic and cassava brown streak virus
pandemics in Africa. Virus Res.,159(2):
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FAO. (mimeo)
9. Araham, K., Edison, S., Sreekumari,
M.T., Sheela, M.N., Unnikrishnan
& Pillai, S.V. 2010. Recent progress
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Tropical (CIAT). 2006. Improved
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21. Leihner, D.E. 1980. Cultural control
of weeds. In E.J. Weber, J.C. Toro &
M. Graham, eds. Cassava cultural
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Salvador, Bahia, Brazil. March 18-21,
1980. pp. 107-111.
Chapter 7: Harvest, postharvest and value addition
1. Martwanna, C., Sarawat, P., Limsila,
A., Tangsakul, S., Wongwiwatchai,
C., Kebwai, S., Watananonta, W. &
Howeler, R.H. 2009. Cassava leaf
production research conducted in
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roots and leaves for on-farm animal
feeding. Proc. regional workshop, held
in Hue city, Viet Nam, Jan. 17-19, 2005.
pp. 66-88.
15. Rojanaridpiched, C., Thongnak, N.,
Jeerapong, L. & Winotai, A. 2012. Rapid
response to the accidental introduction
of the mealybug, Phenacoccus manihoti,
in Thailand. Factsheet prepared for
FAO. (mimeo)
2. Howeler. R.H. 2012. Cassava leaf
production for animal feeding. In R.H.
Howeler, ed. The cassava handbook – A
reference manual based on the Asian
regional cassava training course, held
in Thailand. Cali, Colombia, CIAT. pp.
626-648.
16. IITA. 2004. IITA Brief: Biological
control. Ibadan, Nigeria.
3. Latham, M.C. 1979. Human nutrition
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4. Lutaladio, N.B. & Ezumah, H.C.
1981. Cassava leaf harvesting in Zaire.
In E. Terry, K. Oduro & F. Caveness,
eds. Tropical root crops: Research
strategies for the 1980s. Ibadan, Nigeria,
IITA. pp. 134-136.
5. Nweke, F. 2004. New challenges in
the cassava transformation in Nigeria
and Ghana. EPTD discussion paper No.
118. Washington, DC, IFPRI.
6. Westby, A. & Adebayo, K. 2012.
Production of high-quality cassava flour
to link farmers to markets. Factsheet
prepared for FAO. (mimeo)
7. Ceballos, H., Sánchez, T. & Dufour,
D. 2012. Developing cassava varieties
with unique starch characteristics.
Factsheet prepared for FAO. (mimeo)
8. FAO. 2007. Guía técnica para
producción y análisis de almidón de
yuca. Boletines de servicios agrícolas de
la FAO Number 163. Rome.
9. Howeler, R.H. 2012. Recent trends
in production and utilization of cassava
in Asia. In R.H. Howeler, ed. The
cassava handbook – A reference manual
based on the asian regional cassava
training course, held in Thailand. Cali,
Colombia, CIAT. pp. 1-22.
10. IFAD. 2012. Global consultation on
cassava as a potential bioenergy crop, by
E. Kueneman, V. Raswant, N. Lutaladio
& R. Cooke. Accra.
11. Kanto, U., Tirawattanawanich, C.,
Juttupornpong, S., Promthong, S. &
Moonthong, O. 2009. Advantages of
cassava in animal health improvement.
In R.H. Howeler, ed. The use of cassava
roots and leaves for on-farm animal
feeding. Proc. regional workshop, held
in Hue city, Viet Nam, Jan. 17-19, 2005.
pp. 187-203.
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Oct. 20-24, 2008. pp. 691-696.
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Chapter 8: The way forward
1. FAO. 2012. Save and Grow. A
policymaker’s guide to the sustainable
intensification of smallholder crop
production. Rome.
2. FAO/IBPGR. 1998. Technical
guidelines for the safe movement of
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Feliu, eds. Rome.
3. FAO. 2012. Food outlook. Global
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4. San Miguel Pure Foods. 2009.
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de Ora, Mindanao, Philippines, 12-15
October 1999. Canberra, ACIAR.
pp. 32–53.
6. Howeler, R.H. 2008. Results,
achievements and impact of the Nippon
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Abbreviations
CGIAR Consultative Group on International
Agricultural Research
CIAT International Center for Tropical
Agriculture
CBSD cassava brown streak disease
CMD cassava mosaic disease
CTCRI Central
FAO Food and Agriculture Organization
of the United Nations
FFS farmer field school
FPR farmer participatory research
GDP gross domestic product
ha hectare
IFAD International Fund for Agricultural
Development
IITA International Institute
of Tropical Agriculture
IPM integrated pest management
ITPGRFA International Treaty
on Plant Genetic Resources for Food
and Agriculture
K potassium
K20 potassium oxide
N nitrogen
NGOs non-governmental organizations
P phosphorus
P2O5 phosphorus pentoxide
t tonne
TUUSI Technology Uptake and Upscaling
Support Initiative
copertina cassava save and grow.pdf
1
25aprile2013
12.00
C
M
Y
SAVE AND GROW
SAVE AND GROW: CASSAVA
This guide is the first on the
practical application of FAO’s
“Save and Grow” model of
agriculture to specific
smallholder crops and farming
systems. It comes as cassava
production intensifies
worldwide, and growers shift
from traditional cultivation
practices to monocropping,
higher-yielding genotypes, and
greater use of agrochemicals.
Intensification carries great risks, including soil nutrient
depletion and upsurges in pests and diseases. The guide shows
how ecosystem-based “Save and Grow” approaches and practices
can help tropical developing countries to avoid the risks of
unsustainable intensification, while realizing cassava’s potential
for producing higher yields, alleviating hunger and rural poverty,
and contributing to national economic development.
CM
MY
CY
CMY
K
A GUIDE TO SUSTAINABLE PRODUCTION INTENSIFICATION
FAO
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