5046 Cropping Booklet - Department of Primary Industries, Parks

5046 Cropping Booklet - Department of Primary Industries, Parks
Managing Tasmania's
Cropping Soils
A practical guide
for farmers
Bill Chilvers 1996
Published by the Department of
Primary Industry and Fisheries, Tasmania,
and the National Landcare Program.
ISBN 0 7246 4280 3
Original publication printed by Richmond Printers, Devonport.
PDF file - Colin Vercoe Design. 2000.
Refer to this publication as:
Chilvers W.J. 1996 Managing Tasmania’s Cropping Soils – a practical guide for farmers.
Department of Primary Industry,Water and Environment, Tasmania, Australia.
Front cover: preparing another seedbed at Kindred on
Tasmania’s most valuable cropping soils, the kransozems.
INTRODUCTION ........................................................................................................
Good crops grow in degraded soil - don’t they? .................................................................
What makes a good cropping soil? .....................................................................................
Farm planning for cropping farms....................... ...............................................................
The importance of organic matter ......................................... ............................................
What soil management types do I have? ............................................................................ 11
Before we set to work - two key checks
- roll test for soil moisture .................................................................................... 12
- a pit investigation for compaction ...................................................................... 13
Krasnozems - red clay loams on basalt ................................................................
Cressy soils - clay loams on tertiary sediments ....................................................
Black Cracking Clays - on basalt or dolerite hills, or recent alluvium ................
Duplex Soils - sandy loam over clay on tertiary sediments .................................
Deep Sands - windblown deposites ......................................................................
Drainage.............................................................................................................................. 58
Sodic soils ........................................................................................................................... 63
Cover crops ......................................................................................................................... 65
Direct drilling and local drill conversions ..........................................................................
How the implement breaks the soil ....................................................................................
Tines ...................................................................................................................................
Discs ...................................................................................................................................
The mouldboard plough .....................................................................................................
Powered implements............................................................................................................
Choosing the right implement ............................................................................................
Tillage is very subjective. Every tillage implement can be found working on every soil type, and it’s
appropriateness reasonably argued. Good soil management lies in the way the implement is operated and
the soil conditions at the time. There are no text book answers or receipts to follow as you stand in the
paddock deciding on how to prepare the seedbed. This manual is a mix of broad guidelines and local
farmer examples. You are welcome to disagree, because debate and discussion amongst neighbours and
farming groups can only improve the way our soils are managed in the long run. It’s up to you to make
the decisions and your best tools are a spade to investigate and a willingness to learn.
Cropping is most intense on the krasnozem soils of the north west coast of the state. Intensive tillage
using powered implements and mouldboard ploughs is sustainable on these resilient soils if they’re managed with care. Less resilient soils in the Midlands, Coal River and Derwent Valley regions are being
cropped with increasing intensity. Sandy soils, shallow duplex soils, sodic soils and black cracking clays
all behave very differently from krasnozems. The intensive tillage used on krasnozem soils is not sustainable on these other soils. Structure, drainage, erosion and productivity are suffering as a result.
This manual identifies five basic soil types, and indicates how they might be managed appropriately so
the resource is maintained or improved for the future. The five types of soil identified in the manual are
broadly defined on the basis of management. These are soil types that can be, and should be managed in
a particular way. Don’t worry if your soil doesn’t fit the photograph exactly, since each of the five types
embrace a wide variety of soil depths, colours and textures. The detailed description is included to bring
together soil pedology (soil description), and soil management, two disciplines which benefit greatly by
being side by side. Join a Whole Farm Planning, Topcrop or Farm Best Practice program to find out more
about your soil.
For more information on pedology, consult the yellow book; Australian Soil and Land Survey, field
handbook, 2nd Ed, McDonald RC, Isbell RF, Speight JG, Walker J and Hopkins MS, Inkata Press, 1990.
For those who would like to read more on soil management and implements, I recommend Soil Management, 5th Edition by Davies, DB, Eagle DJ, Finney JB, Farming Press, UK 1993.
This manual is all about fostering appropriate soil management practices for different cropping soils.
I would like to thank Bill Cotching for originating the project and his patient supervision. Also to Bill
Gibson for his special effort reviewing the manuscript, and the many others who made suggestions for
improvement. Thanks to the case study farmers who discussed and shared their soil management expert
expertise with me, particularly those who became case studies. I would like to thank the Farm Best
Practice and Topcrop programs for providing numerous opportunities for valuable in paddock
discussions. Finally I would like to thank the National Landcare Program and the DPIF for their
financial support.
Good crops grow in degraded soil
- don’t they?
On our rich red krasnozems, after 100 years of erosion and
structural decline, we appear to be successfully growing crops in
cloddy, compacted subsoils. These degraded soils erode easily,
are awful to work, contain little organic matter and few earth
worms or living things. But the fact is the crops still grow, and
we continue to make a living - so why worry?
A degraded soil requires high
inputs and first rate management
to produce reasonable crops.
Excellent crops only happen
when ‘everything goes right.’
In the midlands and Coal River valley on shallow duplex soils,
many have gradually deepened the topsoil by ploughing in a little
subsoil each time, we have heavy tractors and harvest trucks compacting pores in the underlying clay, we
have dust storms sometimes burying a few wires on the fence, and we have powered implements to beat
clods into submission. And the crops still seem to grow - so why worry?
Why worry? Because the RISKS increase and the COSTS increase.
The RISKS are that we lose all the buffers that a healthy soil has:
buffers against pests and disease. A healthy soil has a wide range of organisms that tend to keep
each other in check.
buffers against nutrient deficiencies and toxicities. Organic matter plays a leading role in
minimising leaching of applied fertilisers and supplying the full range of nutrients required for healthy
crop growth.
buffers against waterlogging or drought. A healthy soil is full of holes and pores - large ones for
drainage and small ones to hold moisture for crop growth. Have a look! If these are removed by
compaction or overworking, there is less water available for plant growth between the extremes of
waterlogging and water stress.
The COSTS. The clods, the compaction - it all takes more time and
conventional tillage is the only way - once your soil is degraded,
direct drilling failure is more likely, minimum tillage is risky.
Conventional tillage can cost $60 to $100/ha compared with $20 for a
direct drill operation.
expensive harvesting - clods increase labour requirments on potato
harvesters causing potato bruising and associated payment penalties.
extra fertiliser - a degraded soil requires greater inputs
extra herbicides - a degraded soil has greater weed pressure
With farmers’ terms of trade constantly slipping, it’s time to take better
care of our soils because one day it will not be economical to produce
crops in degraded soil.
What makes a good cropping soil?
Before we look at differences between soils, let us
ask what is common to all the cropping soils.
Apart from being sufficiently fertile, a cropping
soil has to satisfy three physical requirements, not
without some conflict:
soil strength to avoid excess sinkage and
wheel slip. High bulk density.
be suitable for plant growth - must contain
sufficient pores for aeration, drainage and
water holding. Must be friable to allow root
extension and proliferation. Low bulk density.
resist erosion - must be sufficiently structured,
surface covered or protected by conservation
earthworks (banks and ditches)
Soil needs to be of low bulk density for plant
growth on one hand, and of high bulk density for
carrying traffic on the other! A tricky
compromise. As cropping becomes more
intensive, soil management becomes a balancing
act that every so often, goes horribly wrong.
have a high bearing capacity to carry tillage
& harvest traffic - must have sufficiently high
Managing the conflict
The following management tools can
be applied to any soil type under
cropping to minimise this conflict and
assist in sustaining your soil as a
‘good’ cropping soil into the future;
1. Lower tyre pressure. While axle
load determines depth of compaction,
tyre pressure determines the degree of
compaction. The addition of dual
wheels to a tractor will have minor
benefit unless the pressure of all four
tyres is reduced. More information on
page 73.
2. Tramlines. Narrow tyres with high
pressure form a highly compacted
wheeling without affecting crop
growth. Used for all spray and
fertiliser applications between sowing
and harvest.
3. Bed systems. The bed remains for
the life of the crop. eg onions, carrots
and pyrethrum. Subsequent tillage is
4. Permanent beds. This system is
the only one to actually remove the
compromise altogether. All traffic is
permanently restricted to the
wheelings between beds, eg Forth
Farm Produce at Forth or lettuces at
Housten’s Egg Farm, near Cambridge.
Lettuces in permanent beds, Cambridge.
Permanent bed wheelings, ideal for wheel traffic.
Farm planning for cropping farms
- how to make cropping different soils successfully, a practical reality
The physical layout of the farm should reflect its most valuable natural resource - the soils. Different
soils require different management. This is far easier if paddocks contain only one soil type. For many
farms however, soils are such a
patchwork that this is impossible, and
the whole paddock must be managed
to conserve the most erodible or
fragile soil type.
Permanent fencelines follow
major soil type boundaries
Whatever cropping or irrigation
system you might adopt now or in the
future, the farm should be subdivided
based on major soil type differences to
allow appropriate management.
Obtain an aerial photograph of the
farm from the Land Information
Bureau, GPO Box 44A, HOBART (ph 002 338011), and place a plastic overlay on it. On the overlay:
1. mark permanent creeks, dams, and deep, arterial surface ditches
2. draw boundaries around areas of same soil or similar management type
➢ these boundaries will be permanent fencelines. They can be integrated shelterbelts, cutoff ditches
and laneways
➢ temporary fencing can be used to subdivide these areas according to present irrigation run lengths,
thus retaining flexibility for future changes like a different hose length, a hard hose traveller,
centre pivot or moveable solid set
➢ areas with too much soil variation to fence separately must be managed to preserve the most
fragile or erodible soil
Similar management soils - soils which go together well
➢ Duplex and sandy banks - under a ‘topworking’ and direct drilling cropping system
which retains a surface cover against wind erosion at all times
➢ Cressy soils and black cracking clay - these are all dominated by clay and suffer from
clods and poor drainage. They can be mole drained and worked under a topworking or
ploughing system at exactly the right moisture content every time.
➢ Alluvial soils are very variable but usually dominated by clay. They can be managed as
clay soils.
Soils which do NOT go together
Duplex with black cracking clays - duplex soil areas commonly contain black cracking
clays in drainage lines. Fence these separately and manage differently wherever
➢ Krasnozem with sands or off-coloured sandy loams, as found in Wesley Vale or
Scottsdale for example. Fence and manage differently wherever possible
Attending a DPIF Whole Farm Planning course will give you skills in farm mapping as well as
information on financial and risk management, estate planning and biodiversity.
The importance of organic matter
Biological activity continuously breaks down coarse crop and pasture residues into very fine material
called humus. Humus is what gives the topsoil its dark colour. Both coarse and fine organic matter are
essential. Compared with pasture or forest, prolonged cropping results in less coarse material entering the
chain, so humus levels tend to diminish:
Coarse (easily seen)
plant roots & residues
Coarse residues aid infiltration and
protect the soil from erosion. They
keep your soil biologically healthy.
Fine (less than 0.002mm)
Biological activity of
worms, insects, fungi
& bacteria
Humus is vital for maintaining soil
structure and fertility. It helps hold soil
aggregates together under the stresses
of cultivation and heavy rainfall.
Measuring organic matter
The best test is ‘organic carbon’ which measures
the full size range of organic matter from the very
coarse to the humus. ‘Loss on ignition’ is a simple
and cheap test which unfortunately measures
several non-organic soil components. The results
of a loss on ignition test can be misleading for clay
soils which release residual moisture at ignition
temperatures. Different laboratories vary in the
extent to which may seive out coarse organic
matter during sample preparation. If you have
traditionally used the loss on ignition test, it’s ok
for comparison provided you stick with the same
What is a reasonable level ?
Knowing the level of organic matter in your soil
over time is a valuable means of assessing the
sustainability of your cropping program. Take a
sample from paddocks at the beginning and end of
a cropping rotation to see how far you’ve run the level down. See how it compares next time the paddock
reaches this stage. Did the level recover sufficiently during the pasture phase?
A vicious circle. Depleted organic matter levels leave the soil
prone to clods and crusting. Intensive tillage is used to overcome these problems which further depletes organic matter.
An approximate guide to organic matter levels for Tasmania’s cropping soils.
Laboratory test
krasnozem, black
cracking clay &
duplex soils
Organic carbon %
high >5
med 3-4
low <3
high >4
med 2-4
low <2
high >3
med 1.5-2
low <1
Loss on ignition %
high >25
med 15-20
low <10
high >20
med 10-20
low <5
high >10
med 4-6
low <2
High (virgin), medium and
low (heavily cropped) values
for each soil type.
Why does each soil type have such wide variation?
1. cold temperature - slows biological activity. Soil in a colder area of Tasmania tends to have more
organic matter as plant residues and humus build up faster than they break down.
2. annual plant growth - where soil moisture is non-limiting for most of the year, plant growth and soil
organic matter are higher compared with dry areas. This holds true on a farm level and on a regional
3. high clay content - humus becomes intertwined and incorporated in the clay microstructure where it is
protected from breakdown. Thus a clay loam will contain more organic matter than a sandy soil.
How much is returned in roots & tops?
Organic Material Returned By Various Crops (t/ha)
dry matter
1 year
oats green cowgrass
*cereal harvested and all stubble returned
Sources: Wright, DN and Sparrow, LA, Nitrogen cycling and soil fertility in cropping sequences on krasnozems, unpublished
project report, Dept of Agriculture, Tasmania, 1987. Soil Management Fifth Ed, Davies, DB, Eagle, DJ and Finney, JB,
Farming Press, United Kingdom 1993.
How much effect does a green manure have?
About 25% of the coarse organic matter entering the soil forms humus, while 75% is respired to the
atmosphere as carbon dioxide during the first year of its decomposition. The box below shows how many
green manure crops would theoretically raise organic carbon by a 1% unit.
Organic matter fixed by a vigorous, thick stand of green oats
dry matter yield
humification factor for green manure
humus fixed (6t/ha x 0.25)
approximate weight of 20cm topsoil
increase in organic carbon from one green manure crop
number of green manures to increase organic carbon by 1% unit
How much effect does cereal stubble have?
A cereal stubble has a slightly higher factor of about 30%*. About 17 stubbles of 4t/ha each would be
required to raise the organic carbon by a 1% unit.
* from Soil Organic Matter and Nitrogen Management in Dryland Cropping Systems, Technical Report No 211, S.A. Dept of
Primary Industries, August 1993.
Building Soil Organic Carbon is a Life Long Program
Effect of Rotation on Soil Organic Carbon
after 3 year pasture
after 9 year pasture
after 9 years pasture plus 3
plus 3arable
years arable
% Organic carbon
clay loam
silt loam
Source: Jenkinson, DS & Johnston, AE, (1977), Soil organic matter in the Hoosfield barley experiment, Rothamstead
Experimental Station report, 1976.
The rate of build up of your soils organic carbon is very slow.
Note that the rate of loss under conventional cropping is
much faster. If the aim is to increase soil organic matter
significantly feedlots, dairy and poultry farms can supply
manure, but rates of application need to be in the order of
10-40 tonnes/ha.
Topworked onion paddock. Plenty of course
cereal straw on the surface prevents erosion
and crusting. Coal River Valley 1995.
What soil management types do I have?
This manual has five management types, usually fairly easy to
The 5 management types:
distinguish. However, if you are unsure which type you have, a
➢ Krasnozem soils
field texture test is a
➢ Cressy soils
quick and simple way
➢ Black cracking clays
to find out. Texture
➢ Duplex soils
refers to the
➢ Deep sands
proportions of sand,
silt and clay in the
soil. Take a
tablespoon sized sample from the topsoil and go through the
following steps;
Step 1.
Form the sample into a ball by moistening
with water and kneading it. Knead for 1-2 minutes while
adding more water or soil until it just fails to stick to the
fingers. Sand grains produce a rasping sound and feel gritty.
Assess feel and sound according to the chart below.
Step 2.
Press the soil between the thumb and
forefinger to form a ribbon. The ribbon should only be 23mm thick.
The heavier the soil the longer the ribbon.
Gritty and rasping sound
cannot be moulded into a ball
Loamy sand
Gritty and rasping sound
will almost mould into a ball but
disintegrates when pressed flat
about 5
Sandy loam
Slight grittiness, faint
rasping sound
Feels smooth and spongy
moulds into a cohesive ball which
fissures when pressed flat
moulds into a cohesive ball which
fissures when pressed flat
Clay loam
Very smooth, slightly
sticky to sticky
plastic, moulds into a cohesive ball
which deforms without fissuring
Clay loam
Very smooth, slightly
sticky to sticky
plastic, moulds into a cohesive ball
which deforms without fissuring
Clay loam
Very smooth, slightly
sticky to sticky
Very smooth, sticky
to very sticky
plastic, moulds into a cohesive ball
which deforms without fissuring
very plastic, moulds into a cohesive ball
which deforms without fissuring
*Duplex soils have a clay subsoil
Before we set to work - two key checks
In the preceeding chapters we have identified which of the five soil management types we have on our
farm. Now we come to actually preparing a seedbed. We have driven across the paddock and possibly
walked on it. All too often this is the extent of soil assessment. Properly assessing the soil moisture,
cloddiness and compaction are key steps in determining your paddock preparation plan. Reading this
manual will improve your soil management only if YOU get in the habbit of having a close look at
YOUR soil prior to working.
Check 1. Is my soil too wet to work?
Working the soil at too high a
moisture content causes
compaction. Compacted topsoil
results in clods. Compacted
subsoil restricts drainage and
rooting and is more difficult to
alleviate than topsoil compaction.
Which soils are degraded by working too wet?
➢ topsoils containing clay - krasnozems, Cressy soils,
black cracking clays
➢ sandy loams, these also contain some clay and can
become cloddy
➢ subsoils of all soil types including duplex soils where
subsoil pores are closed up by compaction
The roll test for soil workability.
A simple test is to take a hand sample of
soil and work in your hands to an even
consistency. Then try to form a thin
sausage about 3-5mm diameter by rolling
the sample between your palms.
This sample is too wet to work.
A 3mm sausage is easily formed.
This sample is right to work. It
cracks and breaks into short lengths.
If the sample crumbles and a
sausage can’t be formed
- its ok to work but power
requirements will be high.
Test the soil immediately below the
plough layer. Often this will be moister
and thus more likely to result in deep
compaction. Tillage should not be
undertaken if this sample fails the test.
Check 2.
Is my soil too compact?
Indicators of compaction without seriously looking
➢ paddock history - avoiding wet tillage or harvest is not
always possible. If this occurred it’s likely the soil is
➢ surface water ponding - is it worse than usual? This
indicates a compacted surface layer.
➢ wheel ruts - indicate deeper compaction, affecting
drainage and aeration below the plough layer.
➢ patchy crop growth - paddock preparation wheelings
show during growth of the current crop
Assessing compaction requires a look below the
The best way to assess compaction is to dig a hole in the
paddock during a period of maximum crop growth,
because a lot can be learnt from actively growing plant
roots. Compare it with an uncropped area of the same soil
type on your farm. Most cropping paddocks are compacted
to a degree somewhere between the gateway and the
fenceline . Have a quick dig in these places for an obvious
Digging a hole
Dig a small hole about a 30cm deep, noting ease of digging. Come back from the edge of the hole
10cm and extract a neat, undisturbed slice. Carefully break open the slice vertically, looking for pores
and size and shape of soil particles. Compare with the slices from the uncropped area and the
compacted area.
Assess the subsoil - dig through the layer immediately below your usual depth of working. Is there a pan
here? Are roots bent or thickened in and above this layer? Healthy, actively growing roots are very
fibrous, white and of even thickness.
It’s the shape, arrangement
and number of solids
and voids in the soil.
Can you see root channels
and worm channels?
Do the soil particles have rough,
featured faces or smooth faces
with sharp angled edges?
Are there clods?
Are roots penetrating clods?
Surface tilth - is it ‘clods and
powder’ or a complete range of
coarse to fine particles?
Good structure - particle faces are rough
and well featured, with rounded edges,
many cracks and holes making
it friable in the hand.
Poor structure - soil particles are smooth
faced, sharp angled, horizontally
layered, with few cracks or holes.
Roots are not penetrating clods.
General Description
Reddish brown, strongly structured, gradational, clay loam to clay
soils. A darker A horizon indicates a surface accumulation of
organic matter.
➢ water erosion
➢ structural decline
➢ maintaining organic matter
Regions & local names
North West coast from Marawah to Sassafras, Pipers River, Deloraine, Scottsdale, Winnaleah,
Breadalbane, and a small area around Campbelltown. Mapped along the North West of Tasmania as
Burnie clay loam, Yolla clay loam, Lapoinya clay loam
Gently undulating rises to steep hills associated with volcanic lava flows which occurred some 30 to 50
million years ago. Along the North coast, rainfall increases and temperature decreases with distance
inland, and the krasnozems generally become darker, more acidic and higher in organic matter. In the
cold dry climate of the midlands, krasnozems are characteristically bright red with lower levels of organic
matter and high pH. Land capability of areas of Krasnozemsoils generally depends on slope, ranging
from class 1 to 6.
Key properties of krasnozem soils
Moderate. Topsoil depth varies depending on erosion history. Topsoil depth generally decreases and
stoniness increases with distance inland. A particularly loose, fluffy variant is known as ‘snuffy’.
Rapid. Seepage often occurs where impermeable sediments underlying the krasnozem prevent
continued downward movement of water. Soil reaches field capacity in 24 to 48 hours after soaking
rain. Further drying required before tillage.
Root growth
Unrestricted. However, under intense cropping, cultivation pans can develop due to bad tillage
practices and/or excessive trafficking.
High. About 45mm in 300mm depth of topsoil. Compaction reduces available water holding capacity
by squashing soil pores that hold water. 75% of water is extracted by non stressed plants from the top
half of the root zone.
Restricted when wet . Soil must be allowed to dry beyond field capacity before working. A minimum of 3 or 4 fine, drying days after rain are required before the soil is dry enough to avoid damage,
longer if its been cool and cloudy. Cultivating or trafficking wet soil causes compaction.
High (3-5% organic carbon). Intensive cropping without green manure crops or vigorous pasture leys
gradually reduces the organic matter reserve.
Moderate. Strongly linked with organic matter contents in the plough layer. Nitrogen is largely held
in the organic matter fraction, so levels usually correlate closely with organic matter content. Phosphorus is fixed by the clay fraction so continued applications are necessary. Potassium varies widely.
Moderately acid near the coast (5.5-6.5) and strongly acid further inland (5.0-6.0). Acidity generally
increasing with depth. High lime requirement. Typically 2.5t/ha (1t/acre) of lime increases pH by 0.1
unit between pH 5.5 and 6.5.
Eroion risk
High. Steep slopes, intense unpredictable rainfall events, and fine, unprotected seedbeds combine to
make this soil highly vulnerable to erosion. Commonly 2-10t/ha per year (approx 0.2-1.0mm depth)
under intensive cropping. Topsoil already completely removed from many hill tops and steep banks.
Low. Sometimes repellent after severe drying, particularly if organic matter levels are low.
Occaisional, significantly reducing land capability for cropping.
- our rich red soils
Major challenges
Burnie Clay Loam profile - from Kindred
Australian classification: Ferrosol
Northcote classification: Gradational
Geology: Tertiary Basalt
Runoff: moderately rapid
water erosion
structual decline
maintaining organic matter
Drainage: well drained
Depth cm
Dusky red; heavy clay loam; strong medium (20-50mm) structure and strong very fine
(2-5mm) structure; few ironstone nodules; abundant very fine roots; field pH 6.0
Dark reddish brown; light clay; strong medium (20-50mm) structure and strong very
fine (2-5mm) structure; few ironstone nodules; many fine roots; field pH 5.9
Dark reddish brown; light clay; strong coarse (50-100mm) blocky structure and strong
very fine (2-5mm) structure; few ironstone nodules; many fine roots; field pH 6.1
Dark reddish brown; light clay; strong medium (20-50mm) structure and strong very
fine (2-5mm) structure; few ironstone nodules; many fine roots; field pH 5.7
Red; light clay; few yellowish red mottles; strong medium (20-50mm) structure and
strong very fine (2-5mm) structure; no live roots; field pH 4.8
Strongly brown; light clay; many dark red mottles; common (10-20%) dispersed basalt
gravels; no live roots; field pH 4.5
Combine tillage
implements to avoid overworking and compaction.
Maintaining organic matter levels is a major
challenge for managing krasnozems under
intensive cropping.
Cover crops help reduce erosion.
Keeping our krasnozem soils in good shape
Intensive cropping places great demands on our rich red soils. For a krasnozem to remain healthy under
intensive cropping, management must be first rate. In order of priority, the three key areas of
management are:
1. preventing erosion
2. maintaining structure
3. maintaining organic matter
Preventing erosion is number one. A poorly structured paddock, low in organic matter’, can be restored
under a decade or two of pasture, but a millimetre of soil takes hundreds of years to form. Keeping your
krasnozem in good shape naturally reduces it’s erosion potential - a stable, friable, open structure
maximises infiltration and reduces harmful runoff. Maintaining organic matter levels is a key to good
structure. The three key areas are closely inter-related. Soil conservation earthworks alone can only save
so much soil. Erosion is minimised if soil conservation earthworks are combined with good structure and
lots of coarse organic matter.
The following pages will help you keep your soil where it belongs.
Soil conservation for krasnozems
Divert run-off which is coming
onto the paddock.
They are built in summer or
early autumn.
Cut-off drains are cheap
and effective.
Collect run-off from within the
crop and divert it into grassed
irrigator runs or waterways.
These must be put in
immediately after planting.
are used to safely take the
water from the contour
drains off the paddock.
They are permanently
sown to grass and prepared
12 months in advance.
are a wide shallow drain
along a natural drainage line
permanently sown to grass.
They are prepared 12 months
in advance.
The following two pages discuss these four aspects in more detail. Contact the DPIWE Soils Offices for
soil conservation advise and a farm visit, free of charge.
If you have water coming from outside the paddock;
cut-off drain
diversion bank
Cut-off drains are designed to cut across
slope, often following farm tracks or
fencelines, diverting run-off from its natural
line of flow.
Cut-off drains are usually built with an
excavator. Batter side slopes according to
stability of the soil type; 45degrees for
krasnozems, black cracking clays or Cressy
soils, to 20 degrees or less for lighter soils.
Cut-off drains are usually 50cm to 1m deep.
Where the fall on the drain exceeds 5% on
clay soils, a grassed waterway is necessary.
A cut off drain taking road run off, Kindred.
If you have a natural drainage line
running through the paddock
grassed waterway
A waterway allows runoff to follow its natural course,
however steep it may be. Make the bottom wide (up
to 1m) and level. Throw a mixture of ryegrass and
clover seed on immediately after construction.
A grassed water way follows the natural drainage
line, Lillico Road, Forth.
If you are cropping an area with even a slight slope
grassed irrigator lanes
contour drains
Grassed irrigator lanes hold the irrigator on its track and collect runoff from the contour drains. The lanes
are normally 3.0m wide and need only be 100-200mm deep unless on a sideslope. Install when the
paddock is still in pasture. Distances between runs must be calculated according to spray boom widths to
ensure the runs are not sprayed with herbicide. See the Kindred booklet for details.
Krasnozems – our rich red soils
An onion paddock at Penguin well protected with grassed irrigation runs and contour drains.
Contour drains, installed with a grader blade or spinner drainer, need to be correctly surveyed using a
clinometer to avoid erosion or deposition. They must have between 5 and 7% fall on krasnozems and 0.5
to 2% on sandy soils. See the Kindred booklet for details.
Approximate distance between contour drains
Steep (15%+)
Medium (10-15%)
Low (10% or less)
Heavy krasnozem
less than 30m
more than 40m
Sandy loams
less than 20m
In 1994, the Kindred Landcare group
published ‘Keeping Your Soil On Your
Farm’, a farmers guide to planning and
constructing soil erosion control measures.
For anyone with water erosion problems
this publication is highly recommended.
Copies are available from the DPIWE
office, Stoney Rise, Devonport.
Management Guidelines for Krasnozem Soils
1. Assess paddock for erosion potential before ploughing. Think in terms of catchments and
drainage lines.
2. Avoid steep slopes and long slopes. Don’t crop land over 20% slope. Divide long slopes
with contour drains or diversion banks.
3. Divert external runoff. A single well placed cut-off drain can save your paddock year after
4. Establish grassed waterways. Leave natural drainage lines unploughed. Interruptions to
tillage and spraying operations are minimal.
5. Consider planting layout. Permanent grassed irrigator lanes provide a safe drain to dispose
of water from contour drains. Grassed headlands help keep trucks off the paddock.
6. Install contour drains - immediately after sowing. A long slope is a high risk slope, even if
its only gentle.
7. Cover crops reduce erosion. Fewer contour drains are required if a cover crop is present.
8. Avoid wet harvests. One wet harvest will undo years of careful soil management.
9. Incorporate crop residues. Organic carbon is a key indicator of the sustainability of your
cropping. Use the plough rather than a deep, slow, powered implement pass to incorporate
large amounts of organic matter.
10. Sow a green manure - immediately after harvest. Long fallows are not good for long term
soil structure and fertility. Short term ryegrass is the best soil rejuvinator.
Deep rip at the friable
moisture content. Ripping
moist or wet soil creates clods
below the surface.
Underwork rather than
overwork our rich red soils.
Don’t prepare a seedbed any
finer than is necessary for the
seed being sown.
Shallow chipping/incorporation of barley stubble with a rotary hoe.
Krasnozems – our rich red soils
Krasnozem case studies
Colin Parsons, Cropping farmer/contractor, Forth
mainly krasnozem, with some grey sandy loam patches
dryland cereal in the rotation
pasture/oat potato preparation
approx 75% of farm under crop, 25% under pasture
cropping rotation usually five years long, (potatoes, peas, poppies, onions and triticale), always containing a cereal for groundkeeper and disease control, and to help restore the ground.
Green Manure
Colin traditionally used oats but has changed to short term ryegrass (9-12months) because:
a. oats leave the ground very wet for early spring cultivation
b. ryegrass is a superior green manure for soil rejuvenation
c. ryegrass provides more feed than oats
➢ ryegrass does require irrigation to germinate in summer to produce good growth for grazing and then
ploughing in August/September
➢ time between crops is an opportunity for green manuring and grazing. Colin tries to avoid bare
fallowing any longer than 6 weeks
➢ Colin sees many benefits of a cereal in the rotation;
a) good control of potato ground keepers
b) good disease break to soft rots and wilts
c) lets the ground dry right out, producing deep cracking and clod weathering which enhances
soil structure naturally
d) cereal stubble decomposes slowly, enhancing soil structure and reducing erosion risk
Apr soil test
Apr paraplough x2
oat & fertiliser mix spun on
power harrow to 75mm (3")
leave, turf breaks down
Aug lightly feed off oats
Oct mouldboard plough
power harrow
rip/rotary hoe combination
“your skill as a krasnozem
farmer really shows when you
consistently work the soil at
optimum moisture conditions”.
Primary Cultivation
Colin believes strongly in the use of the mouldboard plough
a) its action on soil structure is relatively gentle compared with powered implements
b) a minimal number of subsequent passes are required to prepare the seedbed
c) effective burial of previous crop’s residues or green manure crop
d) produces a relatively weed free seedbed
➢ Feb mulch stubble
paraplough x 1
oats & fertiliser spun on
power harrow 75mm (3") deep
➢ Sep mouldboard plough
S tine
power harrow
The paraplough
Colin finds the paraplough is far more effective at
alleviating compaction across the whole cultivated
layer compared with a narrow tine ripper
(paraplough 4 tines @ 15", 110hp)
cropping ground is paraploughed at least once per
never paraplough before poppies
dual wheels are very effective at reducing
compaction in seedbeds
Secondary Cultivations
Colin is careful not to work the soil finer than is
necessary for the seed or harvesting operation to
timing is critical - if its too moist, stay off the tractor.
Even a heavy dew on fallow ground significantly
increases structural damage caused by powered
implements or the S tine.
The paraplough tine is angled to follow the soils
natural fracture line. Draught is reduced.
Adjustable lift plates can be seen on the back of
the tines to vary the degree of heave and shatter.
Peter Murdoch, Dairy farmer, Moriarty
krasnozem with patches of Wesley Vale sands and clays
➢ rotaty hoe chipping
➢ roterra/airseeder piggyback
➢ deepest working last
five years pasture between potato crops
Peter uses just two implements, the agroplough and the rotary hoe. This keeps investment in equipment
to a minimum while maintaining flexibility for the different soil types. Lighter soils, being much weaker,
are worked at lower rotor speed and higher ground speed with the hoe.
Krasnozems – our rich red soils
spray off, September
rotary hoe chip 25-50mm (2-3") deep
rip/rotary spikes combination
Peter uses a contractor with a Lely piggyback combination drill to reestablish pasture.
➢ disc
➢ cultivate
➢ roterra/airseeder combination
Charles Langmaid, Vegetable farmer, Kindred
chip pasture with S tine
rip/hoe combined implement
Primary Cultivation - a low energy approach
Charles likes to break up the turf and root mat with his spring tine implement;
a. very little energy is applied each pass
b. the energy is applied where it is needed - to break the turf and no deeper
➢ The combined rip and rotary hoe cultivation helps avoid compaction by
a. reducing the number of passes
b. ordering tillage operations so that the deepest working is as close as possible to the final paddock
➢ spray off herbicide
➢ shallow S tine 50-75mm(2-3") 2 or 3
➢ rip/rotary hoe combination
➢ leave 4 to 6 weeks
➢ rip/rotary hoe combination
Gavin Clarke, Cropping and beef, Red Hills, Deloraine
➢ deep ploughing has reduced
soil workability
➢ tried deep ripping, now
shallow ripping
krasnozems, “fluffy” red to heavy red clay loam
rolling hills, many seepage points
stone limitation
pasture / potato or poppies / peas / barley / onions / pasture
crop phase between 5 and 10 years
pasture is a cocksfoot and ryegrass mix
Green Manure
traditionally oats, but Tama or tick beans preferred after early harvest
green manure is not grazed
spray off depending on twitch
mouldboard plough to 150mm (6")
leave 2 or 3 months
rip to 300-375mm (12-15")
roterra with crumble roller
Deepening topsoil brought problems
ploughed deep at least 200mm (8”) for several years
incorporating a little subsoil each time with the aims of
deepening topsoil and incorporating green manure, but found
a) topsoil gradually more difficult to work, particularly baking
into clods after ploughing, and
b) too many stones were brought up
➢ recently changed to shallower ploughing
‘This year we are settling on a
5” ploughing operation. You
can achieve reasonable incorporation without bringing up
➢ spray off
➢ mouldboard plough to 100mm (4")
➢ graze unincorporated tops with sheep in
dry conditions
➢ roterra with crumble roller
when rippers were first introduced 5 years ago, Gavin ripped up to 20 inches deep everytime. Crop
growth certainly improved. Now Gavin rips 300-375mm (12-15") and only before and after potatoes
and onions, and still seems to be bringing up as much stone as ever!
➢ our decision to rip is based on roterra performance - if it rides out of the ground then ripping is required.
Combined Implements
Rip/harrow combination used before oat sowing
drill/harrows/roller combination used for Tama sowing
roterra - thinking of towing a light Cambridge behind
Tines or powered implements for secondary cultivation
The main problem with the S tine after ploughing is the wheelings, particularly for peas. The s-tine is
used only if stone prevents roterra operation
Handling pea and barley stubble
pea straw - after raking and baling, the stubble is mouldboard ploughed for green manure oats or
Tama, then mouldboard ploughed again, turning the rotted pea straw back on top. This produces
excellent surface tilth and erosion risk is reduced
➢ barley stubble - after hard grazing the paddock is shut up over winter to allow regrowth before a
roterra or mouldboard plough spring seedbed preparation
Krasnozems – our rich red soils
Mike Radcliffe, Wesley Vale
➢ grassed irrigation lanes in
all cropping paddocks
➢ grassed waterways & cut-off
drains as required
➢ roterra-airseeder combination implement
Predominantly krasnozem with areas of sand and duplex
typical of Wesley Vale region
Continuous cropping with two crops per year on the better
ground between the months of September and April.
Organic Matter & Green Manure Crops
Michael believes high soil organic matter is the key to sustaining continuous intensive cropping on the
krasnozems. Some paddocks are shown below:
Typical Organic Matter Levels (% loss on ignition)
Good krasnozem
Poor krasnozem
Wesley Vale Sand
Michael sowing Concord green manure with
his combination roterra/airseeder.
Every paddock is sown in autumn,
usually with Tama ryegrass up until mid
April, or oats if later. Michael avoids
leaving ground fallow over winter
because while nothing is growing, no
organic matter is going back into the
soil, it’s only being lost.
Whether it’s oats or Tama, the seedbed
preparation is absolutely minimal.
Often just spin oats over the previous
crop residue and shallow disc, Lely or
Kuhn, or use the Lely/airseeder
combination drill to sow the Tama. The
sowing boots on the Lely/airseeder are
very lightly sprung, so provided ground
speed is reduced, the boots follow the
surface of an unlevel or roughly
prepared seedbed very well.
Primary Cultivation
Michael generally uses the agroplough and powered implements,
but relies on the mouldboard plough and a shallow powered
implement pass for spring preparation when the soil is too moist
for the agroplough.
“Plastic mouldboards allow
ground preparation with
minimal damage to the soil in
moist conditions - when no other
implement could touch it.”
spray off late August
flail mulch & leave a month
chip with rotary hoe 50mm (2") if necessary
agroplough 300-350mm (12-14")
Kuhn spikes 100-150mm (4-6") incorporation
The rotary hoe, Kuhn spikes and Lely are all used depending on the degree of chopping or mixing
required. However, the Lely is definitely the most expensive machine to maintain.
Secondary Cultivation
Most residues are returned for long term benefit to the soil. Stocking or baling is avoided.
➢ chip stubble with rotary hoe 50mm(2")
behind harvester
➢ agroplough 300-350mm(12-14")
➢ Kuhn spikes 100-150mm (4-6") incorporation
➢ sow beans
Whole Farm Planning
The farm is a prime example of good whole farm planning. Windbreaks, gravelled laneways, ditches
and soil conservation earthworks are well integrated so each poses minimal interruption to the
intensive cropping program.
Soil Conservation
In 1995, Michael enlisted the help of local DPIF soils officers to survey all his paddocks for
grassed irrigator lanes, which he then installed himself using a rotary drainer. Unlike many early
grassed irrigator lanes constructed with a road grader, these lanes are shallow, (100-200mm) just
enough to hold the irrigator and take the water. They’re easy to put in and cause minimal
interruption to paddock operations. Irrigation lanes never have to be measured out again.
However, achieving perfect alignment and number of beds between the lanes remains a problem,
especially with contract sowing on sideslopes.
Krasnozems – our rich red soils
Cressy soils
Major challenges
structure decline (clods, hard pans)
maintaining organic matter
Lots of worm and root channels, critical
for drainage and structure of a heavy
soil like the Cressy, are easily closed up
by compaction.
Does your soil have them?
Severe compaction
Some profiles have gravelly
layers at depth. These areas
can be drained with a few
deep, open ditches.
Cressy profile - from the regional irrigation scheme
Australian classification: Dermosol
Northcote classification: Gradational
Depth cm
Geology: Tertiary clay
Drainage: Poor
Runoff:Moderately rapid
Very dark brown; clay loam; moderate very fine (2-5mm) subangular blocky
structure; abundant very fine live roots; abrupt smooth boundary;
Dark brown; gravelly clay; moderate fine (5-10mm) angular blocky structure;
many very fine live roots; clear wavy boundary;
Strong brown; clay; common coarse faint dark yellowish brown primary mottles; moderate medium (20-50mm) angular blocky parting to moderate very
fine (2-5mm) angular blocky structure; common very fine live roots; clear
smooth boundary;
Yellowish brown; clay; many medium prominent red primary mottles; moderate
medium (20-50mm) angular blocky parting to moderate very fine (2-5mm)
angular blocky structure; few very fine live roots; gradual smooth boundary;
Yellowish brown; clay; few coarse prominent red primary mottles; weak
medium (20-50mm) angular blocky parting to weak fine (5-10mm) angular
blocky structure; few very fine live roots
2426 26
- drainage is the key
General Description
Structure decline (clods, hard pans)
maintaining organic matter
Dark grey-brown to brown, loam to clay loam topsoil,
overlying at about 150mm (6") depth a reddish brown to
grey-brown rather friable clay on brightly coloured, mottled, brown clay.
Region and local names
Westbury, Hagley, Bishopsbourne, Whitemore, Cressy-Longford irrigation scheme
Cressy soils are mapped as Cressy shaley clay loam and Kinburn
On tertiary sediments. Very gently undulating hills and terraces, with the darker, heavier Kinburn soil
occurring in hollows and drainage lines. Land capability of areas of these soils is typically 3 to 4.
Key properties of Cressy soils
Moderate. Cressy shaley loams grade to heavier, darker soils in the drainage lines (mapped as
Imperfect. Drainage design, cost and effectiveness depends on presence or absence of
ironstone gravel in the profile. Install surface drains first. Mole drainage may be a suitable
secondary treatment but seek professional advice.
Root growth
Restricted. Typically these soils waterlog in winter. This restricts the bulk of plant roots to
the A horizon.
Readily available
Moderate. About 45mm in 300mm depth of topsoil in good structural condition.
Organic Matter
Moderate. 2-4% organic carbon.
Restricted. Cressy soils are less resilient than the krasnozem. They are easily damaged by
wet tillage or heavy machinery. Drainage is essential to avoid wet tillage.
Moderate. Potassium and molybdenum deficiencies common.
Moderately acid 5.5-6.5(1:5 water). Lime requirement far less than krasnozem.
Low in the rootzone but often saline at depth. Surface salinity occurs only in association with
seepage or waterlogging.
Erosion risk
Moderate water erosion risk, particularly on intensively cropped paddocks where organic
matter reserves are depleted and compaction restricts infiltration. Exposed subsoil is commonly observed on slopes and hill tops after ploughing.
Water repellence
Rocks & stones
Ironstone maybe present as gravel,shale or occasional large rocks or as a continuous layer.
Gravel and small shale is soft and poses no major limitation to tillage and crop production.
Management Guidelines for Cressy Soils
1. Drainage. Establish deep surface drains first, according to whole farm plan. Mole
drains maybe appropriate to further improve drainage if cropping intensely. Seek
professional advice.
Work at the friable moisture content. Check soil moisture content before every
tillage operation.
Avoid wet harvests. One wet harvest undoes years of good soil management.
Avoid winter forage crops. Stocking destroys the
natural surface tilth.
...and more drainage
- divert runoff entering the paddock
- establish grassed waterways down drainage lines
- plant up and down slope to encourage surface runoff
Incorporate crop residues.
Organic carbon % is a key indicator of the sustainability of your cropping rotation.
Use the plough rather than a deep, slow, powered implement pass to incorporate
lots of organic matter.
Cressy soils are less resilient
than the krasnozem. They are
easily damaged by wet tillage
and take longer to recover.
They do not have the natural
repair mechanism of deep
cracking, self-mulching black
7. Sow a green manure - immediately after
harvest. Short term ryegrass is best. Long
fallows are not good for long term structure
and fertility.
8. Underwork rather than overwork the Cressy
Avoid working the seed bed any finer or deeper than
in necessary for the crop being sown.
Cressy Soil Case Studies
Ross Gibson, ‘Mill Farm’, Hagley
Cressy shaley clay loam
surface & subsurface drainage
winged ripper, 1pass only required
no powered implements
approx one third of farm under crop
usually poppies / peas / cereal / peas / cereal / cereal, or potatoes / cereal / peas / cereal / cereal
Green Manure
oats after all crops except late
dug potatoes
➢ oats broadcast directly on grazed
stubble, one or two discings
100mm (4") deep.
➢ oats winter grazed
1994/95 CROPPING
broad beans 10
traditionally perennial ryegrass/
white clover mix (Ellet,
Tasdale) for 4 years
➢ traditional pastures not lasting
due to pasture grub damage
➢ about to try short term ryegrass (Concord, Progrow)
➢ deep rips only before potatoes to achieve sufficient depth
of tilth 300mm (12") for planting
➢ winged ripping tines produce a complete soil shattering
with a single pass
➢ no powered implements are used
Winged ripper used by the Gibson’s at Hagley. ➢ mouldboard plough is usually used in seedbed preparations except the oat green manure
➢ discs are used instead of mouldboard plough to conserve moisture in dry years
➢ cereal stubbles are returned by disc or mouldboard plough after grazing and baling
mouldboard plough
leave 4 to 6 weeks
rip with winged ripper
S tine
S tine
remnant stubble could be found mixed throughout topsoil, associated with signs of intense worm and
biological activity
Ross has purchased a European brand of discs with a spacing of 250mm (10") rather than the standard 300mm (12"), with the benefits of finer chopping of stubbles and less ridging during shallow
Cressy soils – drainage is the key
graze stubble with sheep
broadcast oats
disc once
graze over winter
mouldboard plough July
leave 4 to 6 weeks
S tine
S tine
The Gibson’s have an International 511
drill with Superseeder points, but find
the trash clearance and tine breakout
severely limiting any direct drilling
options. An undercarriage purchase or
conversion is being considered.
Hogweed and a compacted surface after peas made direct drilling
difficult. The Gibson’s are keen to modify their drill.
Gordon & Stuart McGee, Bishopsbourne
Cressy shaley clay loam.
2.5 to 3% organic carbon on most cropping paddocks,
which is a reasonable level considering these soils have
been cultivated for 100 years or more.
extensive subsurface drainage
soil ‘more difficult to work’ after
many years of deep ploughing
careful use of rotary hoe
no deep ripping
potatoes / cereal (wheat or Triticale) / poppies or peas
pasture traditionally 2-3 years, now thinking of changing rotation to a system of short term ryegrass
(1year) every 2nd or 3rd crop.
perennial crops of phennel, grass seed and chicory are also grown.
would prefer more perennial crops because the soil rejuvenates under these without tillage, and there
are no annual costs of tillage.
➢ mouldboard plough 200mm (8")
➢ rotary hoe
➢ plant
➢ harvest
➢ shallow disc and S tine, or S tine twice only
➢ sow autumn
Peas or
➢ graze stubble and leave overwinter or
direct drill oats if summer rainfall
➢ mouldboard plough
➢ S tine
➢ plant
shallow disc towing cultipacker
S tine
Peas or
Green Manure
traditionally oats, but grazing animals tend to destroy structure in the top couple of inches. This
compaction is far worse under oats than short term ryegrass.
Primary Cultivation
mouldboard ploughing is used extensively on the McGees’ farm, with minimal secondary passes.
The McGees are very keen to acquire/make a furrow press to further reduce additional tillage passes.
➢ a roller or cultipacker is towed behind every implement to crush clods and avoid baking by
consolidation and moisture retention. The rotary hoe is only used before potatoes.
Deepening the topsoil
the McGees have traditionally ploughed a little deeper
every time, mixing a little subsoil into the topsoil with the
aim of deepening topsoil.
➢ this practice has allowed potatoes to be grown but Gordon
admits the soil has become heavier, more prone to clods
and trickier to manage. Mixing has diluted the topsoil’s
organic matter, reducing soil fertility.
constructing deep surface drains where required was the
first step in the drainage program
approximately half the farm has underground drainage
perforated plastic pipe with gravel backfill is the main
treatment. Success relies on the secondary treatment of
mole drains, installed using a hired bulldozer for $210/ha
at 1.5m spacing. These empty into the pipe drains through
the gravel backfill connection.
1. Grid drainage - for paddocks of even or minimal
slope, 30m spaced parallel drains costing about
2. Strategic drainage - for undulating paddocks with
distinct drainage lines, pipes follow the hollows, and
moles are installed crossing these. Around $750/ha
with drainage, ploughing can be achieved early at optimum and even moisture content across the
entire paddock, towing the roller behind to avoid baking and clod formation.
the McGees can now safely work their drained soils 2-3 days after rain and be assured that smearing
and compaction is not occurring. Clods are the biggest problem with cropping these soils. This is
largely avoided with drainage.
potatoes are the farm’s biggest income (20ha on a 6-7 year rotation), and drainage has removed virtually all the risk of waterlogging or wet harvest. If rain occurs immediately following irrigation, you
don’t have to worry at all. The aim is to finish potato harvest by the beginning of June.
Cressy soils – drainage is the key
Black cracking clays
Major challenges
working at the right soil moisture
clods and smearing
Self mulch tilth of a black cracking clay soil
Deep surface drains are a key to
successful management of alluvial
black cracking clays.
Coal River, lower hillslopes
Australian classification: Vertosol
Northcote classification: Uniform
Geology: Tertiary basalt
Runoff: Moderately rapid
Autumn plough and one pass S-tine in
spring - a minimum tillage preparation
for black cracking clays.
Drainage: Imperfect
Depth cm
Black; heavy clay; massive parting to moderate medium
(20-50 mm) polyhedral structure; common very fine live
roots; abrupt smooth boundary;
Very dusky red; gravelly heavy clay; massive parting to
moderate fine (5-10 mm) polyhedral structure; many
angular stratified basalt gravels (20-60 mm); common
very fine live roots; sharp smooth boundary;
Dusky red; gritty light clay; massive structure; sharp
smooth boundary;
32 32
- sent to test our skills
General description
A black, structured, swelling clay overlies (at 30-60cm depth) a
mottled, greyish brown or strong brown sandy clay. The surface soil,
of light clay or clay loam, is thin (<10cm) and strongly selfmulching, developing a strong very fine granular structure on drying.
➢ working at the right soil
➢ drainage
➢ avoiding clods & smearing
Either on hillslopes of basalt or dolerite parent material where rockiness often limits cropping capability,
or as a recent alluvial deposit along drainage lines, floodplains of creeks and rivers. This soil can occur in
association with other lighter soil types, making separate management difficult.
Regions and local names
Found throughout the state. Local names in mapped areas of the Coal River Valley are Roslyn, Churchill,
Cranston, Laburnam, Dolerite and Basalt 1. In the Midlands, the alluvial black cracking clays are known
as Canola. The land capability of areas of these soils is 4 or lower depending mainly on the frequency of
What is self-mulching?
A special tilth forming
characteristic of these soils.
The ability to form a natural
seedbed during wetting/
drying and freeze/thaw
Typical Canola profile - from the midlands
Australian classification:
Northcote classification:
Geology: Alluvium
Runoff: Moderately rapid
Drainage: Imperfect
Black; light clay or clay loam; generally no mottles; moderate very fine granular structure plus moderate fine
subangular or angular blocky structure; generally no stones; pH 6.0; salinity 0.1 dS/m; clear or abrupt smooth
Black to very dark grey; light to heavy clay; may have few grey and strong brown mottles; moderate mediumcoarse angular blocky structure with some fine granular peds; generally no stones, some profiles may have few
dolerite stones; pH 6.5; salinity 0.2 dS/m; clear to gradual smooth boundary
Black to very dark grey; medium clay; few brown or dark yellowish brown mottles; moderate angular blocky
structure or lenticular structure; few manganiferous and/or calcareous nodules; generally no stones; some
profiles may have few dolerite stones; pH 7.2; salinity 0.5 dS/m; clear boundary
Strong brown or greyish brown; sandy clay or medium clay; common yellowish brown mottles; massive or
medium lenticular structure; few calcareous or manganiferous soft segregations; generally no stones; some
profiles may have few dolerite stones; pH 7.4 salinity 1.0 dS/m.
Key properties of black cracking clay soils
Moderate. As alluvial soils, variation in structure is high, some are horrendously cloddy, some
beautifully friable, perhaps reflecting management history. On basalt or dolerite hillsides,
variation is considered in terms of stoniness and limited topsoil depth.
Self mulching
High. The ability of the soil surface to crumble over time into fine (<1mm) aggregates,
forming a natural tilth by shrink/swell cycles. Encouraged by wetting, drying, frost, and by
avoiding compaction from machinery and stock.
Restricted. Permeability slow after wetting and crack closure. Prone to flooding where
associated with rivers, streams or drainage lines. Under cropping, wet areas become structurally degraded unless drainage works achieve uniform soil moisture across the whole paddock.
Root growth
Restricted. High soil strength constricts roots to natural planes of weakness ie. cracks and
voids. In the topsoil, rooting is dependent on the self-mulching natural tilth formation.
Readily available
High. About 45mm in 300mm topsoil depth. In a clay soil, a large proportion of soil voids are
extremely small, and the water they contain is held too tightly for roots to extract. The soil
may feel reasonably moist in the hand but the plants may be under stress. Holding capacity is
reduced by mismanagement - compaction and decline in organic matter levels.
Organic matter
High. 3-4% organic carbon under cropping, up to 7% under vigorous pasture.
Poor. These are known as ‘Sunday soils’, because they’re too wet to work one day, and too
dry the next. More than any other soil, the key to successful management and long term
productivity lies with timeliness of paddock operations. Encourage the soils inherent selfmulching properties to form the seedbed by ploughing early and good drainage.
High. Inherently high clay and organic matter levels are reservoirs of plant nutrients. May
become deficient in phosphorus and potassium.
Slightly acid, becoming neutral to slightly alkaline with depth.
Variable. Sometimes slightly saline topsoils, salinity increasing with depth.
Variable. Muddy, discoloured puddles and runoff, and slumping or running together of the
surface after mouldboard ploughing are good indicators.
Erosion risk
Moderate. High soil strength and cohesion make these soils comparatively resistant to
erosion. However, erosion does occur on steep or long slopes or in alluvial sites with fast
flowing flood waters.
Water repellence
Rocks & stones
Variable. Rounded
dolerite stonesor
vesicular basalt
Sunday soils at their worst. Maximise the soils natural self mulching
ability to form the seedbed. Install drains and plough early.
These are the most frustrating of all cropping soils. Compared with other soils,
the clods are spectacular and unforgiving, and it has the narrowest moisture
range for working. However, when in good physical condition, their self
mulching characteristics can form a seedbed with a zero-till or minimum tillage.
What are appropriate tillage practices for black
cracking clays? Most of Australia’s wheat,
sorghum and cotton is grown on these soils
where long fallows play an important role,
primarily for moisture conservation, but the
natural self-mulch is certainly promoted. The
depth of friable self-mulch is commonly
10cm(4") or more. This depth of self-mulch is
rarely seen in Tasmania. A comparison of
management is shown:
clods, clods.......
unbreakable clods!
Why are our black cracking clays so
cloddy and difficult compared with
elsewhere in Australia?
1. Ours are stocked heavily which causes severe
surface compaction especially in wet
2. Ours receive more intensive tillage.
Conventional tillage (chisel plough), used
elsewhere in Australia is equivalent to our
minimum tillage. Mouldboard ploughs and
powered implements are not used anywhere
else in Australia on black soils.
3. Ours are poorly drained, and often share the
paddock with other soil types. Tillage occurs
before the black soil areas are really dry
4. Our fallows are rarely longer than 8 months.
Elsewhere fallows of 12-18 months may occur
while sufficient moisture for crop growth
accumulates in the profile. Long fallows
promote a natural self-mulched seedbed, but
reduce long term soil organic matter levels.
On the mainland, the self mulching characteristic of
this soil seems to be stronger, whether as a result of
management, climate or inherent in the soil itself
would require more investigation.
Self-mulch versus tillage
Dryland cotton near Gunnedah, NSW.
Deep cracks and 5-10cm of selfmulch tilth.
In Tasmania, there are two basic approaches to preparing the
seedbed on this soil. Either autumn plough and leave fallow
over winter, or spring plough, forming the seedbed by tillage.
Both options are valid and should be used in a sustainable
cropping program, since, be it a wet year or a dry year, a
complete disaster is avoided, and the workload on labour and
machinery is spread over time.
Autumn preparation- Let the weather do the work
plough early (chisel, one way or mouldboard plough)
leave over winter to self mulch
in spring, one or two very light, shallow workings once dry enough (using dutch harrow, smudge, S
tine with front smudge board or shallow powered implement)
Short term risk - a wet winter or flooding will cause slaking and the whole ploughed layer runs together to
form a massive continuous layer. The surface dries and bakes in the spring, preventing any drying or
movement of the water beneath. By the time its dry enough underneath to bear a tractor, the surface
has baked. Any tillage results in clods.
Black cracking clays – sent to test our skills
Long term risk - organic matter levels build duing active plant growth and decline during fallows. Six
months of crop growth a year is simply not enough to maintain humus levels in the long term, making
the soil gradually more prone to damage by tillage, traffic and stock.
Spring - Form seedbed by tillage
spring plough, towing a roller/press
follow immediately to conserve moisture (dutch harrow, smudge, S-tine with front smudge board or
shallow power harrow)
Short term risk - the surface immediately dries and bakes while the soil below is still too moist for tillage.
Secondary tillage operations result in clods which resist
passive (tined) attempts to form a seedbed. This leaves the
options of high powered ‘bashing’ rotary implements,
option is used,
sowing deep, or sowing and irrigating.
smearing and compaction are by
Long term risk - more tillage leads to poorer structure, then
far the biggest factors in
requiring more tillage........
determining whether your black
cracking clay will improve or
decline over time.
Long fallow or green manure?
A long winter fallow will give you a nice
self mulched seedbed come spring time,
but this is at the expense of long term
sustainability. Humus levels in the soil
build during active plant growth and
decline during fallows. Six months of crop
growth a year is simply not enough to
maintain humus levels in the long term.
Green manures, ryegrass, topworking and
stubble retention are the best tools for
ensuring the soil is biologically active
nearly all year round.
For black cracking clays in bad structural
condition, a long fallow migh be the only
The S-tine with double crumble roller is a key implement.
Maximise wetting and drying cycles
These cycles promote the self-mulching structure. Plan your rotation to include a dryland cereal crop
inbetween irrigated crops to ensure a really severe drying and deep cracking occurs. If several irrigated
crops are grown, the soil never has a chance to really dry and deep crack.
Black cracking clays and depth of ploughing
These soils are often uniform black cracking clay for 60cm or more. Therefore, can’t we just bury the
clods? Unfortunately not. The deeper you go the fewer fracture lines (straw, roots and worm holes), exist
which means deep ploughing will bring up more cloddy clay. Plough shallow, just to the depth of the
friable root zone, usually 100mm (4"). This is the minimum depth for modern mouldboard ploughs.
Shallow ploughing encourages self mulching seedbed formation. (See page 79.)
Management Guidelines for Black Cracking Clays
Work at the friable moisture content. Use the rolling in hand test before tillage. Wet tillage
destroys the soil’s ability to form a natural self mulching seedbed
Promote surface drainage.
➢ for undulating paddocks, open up drainage lines linking hollows and depressions with broad
shallow grassed ditches. Leave unploughed during cropping.
➢ for flat paddocks, plant up and down whatever slope exists to encourage shedding of surface
water down rows or wheelings.
➢ for very flat paddocks, construct beds or parallel shallow ditches on a 20-40m spacing, or
mole drain. Seek professional advice.
Use the natural tilth. Use long fallows rather than tillage in cloddy paddocks. If a good tilth
exists, avoid stocking and direct drill a cereal crop.
Avoid wet harvests.
Decades of careful soil management are undone with one wet harvest.
Avoid stocking in wet conditions. Grazing winter forage crops or oats is highly effective at
destroying the natural tilth by pugging.
Retain stubbles and residues.
Avoid using powered implements to incorporate large amounts. More humus is lost than gained better to burn and ‘topwork’ than ‘hammer’ these soils. Use the mouldboard plough, tines or
Avoid erosion on long steep slopes
Break long slopes with a diversion bank or small contour drains
Don’t crop areas at risk of erosive flooding
Surface drains follow mouldbourd plough finishes.
After surveying, finishes were broadened with a road grader.
Ploughing will gradually crown the land between.
Black cracking clays – sent to test our skills
Black cracking clay case studies
Noel Beven - black soils on dolerite hills
Main Points
chisel plough early and
leave to self mulch
➢ short rotation ryegrass
self mulching black soil on foot slopes of dolerite hills
slopes up to 20 degrees
depth 200-300mm over brown clay (probably mildly sodic/saline)
good structure, plenty of coarse organic matter present
Noel grows various brassica seed crops, tick beans,
onion seed, carrot seed as well as poppies, oats for
grazing/green manure and fresh vegetables.
having cropped continuously for eight years following
a 20 year pasture - Noel believes soil conditions are
better than when they began
all stubbles and residues are mulched
uses short rotation ryegrass pasture
alternates legume/non legume in rotation (peas & beans)
generally chisel plough x2, leave over winter, then Stine or roterra only if necessary
s-tine good except for compacted wheelings
mouldboard plough only for residue/stubble
deep ripping - not used, not convinced of benefit
tows harrows behind final cultivation - one less pass
compaction is major problem - likes to drag boot
across seedbed and find no ridges
very aware of clay soils limited workability, risky soils
Noel Beven cutting broccoli.
for cropping
Erosion down the rows is a major concern.
➢ strong believer in returning lots of organic matter
➢ water erosion is a problem in winter brassicas with beds up and down slope
➢ believes in cultivating to leave fallow rough (ridged) to avoid erosion, capping, & promote natural
weathering, however, a rough fallow does promote moisture loss in dry years
➢ capping is a major problem for poppies in the valley (most black dolerite soils are too coarsely structured
for poppies). If 36 hours can elapse between sowing and rainfall then capping seems to be avoided.
Justin Nichols, Campania road, Coal River Valley
black soils on dolerite and duplex soils
trying continuous cropping
under good soil management
➢ watching organic matter levels
200 acres of irrigated cropping, (80% of farm), with peas, canola,
poppies, barley, oats, broad beans, seed onions/cabbage
duplex soil cropped for 5 years but believes this the limit of the soils capability
black soil, 5 to 6 years is ok, provided its worked correctly (at the right moisture content)
typical rotation - cereal / poppies / peas / canola / cereal
barley stubble feed off, chisel plough and leave rough over winter to self mulch
mouldboard ploughs all bean trash
agroploughs (250mm, 10"), simply to make secondary cultivations much easier and improve
infiltration with very little surface disturbance or mixing
Believes the Coal River irrigation scheme is designed on 3 years cropping in 4 years. These soils are
capable of this intensity of cropping only under the best management. Water costs about $120/ML, so
higher value crops are required (orchard/vine/seed) to take the pressure off the soils by allowing a
longer rotation.
➢ Maintaining organic matter levels is a real concern for Justin, particularly when pastures are so poor
due to grubs and droughts. A concerted effort of green manuring (sorghum or Sudan grass under
irrigation) and return of all crop residues will probably maintain organic matter levels higher than
under a rotation with a poor pasture phase.
Ron & Chris Gunn, ‘Glenquoin’, Teatree
black cracking clay on dolerite hills
on leased block near Richmond - duplex with black cracking clay
drainage lines
➢ one pass between
cereal crops
➢ minimum tillage for
peas and onions
cereals on ‘Glenquoin’
on leased area fed by regional irrigation scheme, crops 5 to 7 years with peas, broad beans, cereals,
poppies and canola, using a short term ryegrass for best cropping paddocks, and perennial pasture in
less frequntly cropped paddocks
Ron and Chris try to minimise their tillage where ever possible, and make best use of the self mulching
ability of their black cracking clays.
chisel plough 1 or 2 times
burn excess straw
The brothers have a six row Shearer trash-culti drill which suits their minimum tillage system well.
Paddocks are either chisel ploughed or disced in autumn, left to self mulch over winter before sowing.
Soil moisture has to be just right to avoid smearing on the black cracking clay soils. “You have to be
prepared to wait around and go when it’s right.” The drill is not converted for direct drilling so stubbles
are grazed and later burnt if too much stubble remains for the drill to pass without blockage. The brothers
say a mulcher would be an excellent tool for chopping stubbles and residues, allowing retention of more
organic material to sustain lengthening cropping rotations.
chisel plough 1 or 2 times
spray off
sow peas
Black cracking clays – sent to test our skills
slash or mulch
S tine
sow onions
David Smith, ‘Park Nook’ (leased), Cressy
Park Nook’s best cropping soils are alluvial brown
clay loam soils on a present floodplain. The soils
crack and self mulch.
➢ The watertable approaches the surface during winter. Most paddocks are undulating and dissected by
old stream channels, with gravel and stone seams at
varying depths.
poor drainage/wet tillage causing
clods & compaction
degraded soils still producing good
crops under good management
Poor drainage means tillage is a continual comprimise between too dry on the banks and too wet in the
hollows. Soil management can be mediocre at best. The main limitation to drainage is the Lake River,
which approximates the depth of the hollows in the surrounding cropping paddocks. Deepening of this
channel would destroy the corridor of native/introduced vegetation and cause a decline in stream quality.
Low lying paddocks and depressions on this farm should not be cropped.
Potatoes, peas, poppies, Pak choi, chicory, brassica seed crops, onions, squash, beans and sweet corn are
all grown with no strictly defined rotation.
Green Manure
About 80ha of the 120ha cropped each year traditionally had an oat green manure over winter. Annual
ryegrass has now largely replaced oats as the green manure.
The same basic preparation is used for all crops using the plough, dutch harrow and roterra:
Oat green
mouldboard plough June/July
leave until final preparation
Dutch harrow 1 or 2 times
roterra shallow/high ground speed towing
roller behind
➢ sow beans
Drainage would remove wet areas of the paddock, allowing a well timed early plough with the
whole paddock at an even, friable moisture
content thats right for ploughing and working.
Which is the lesser of two evils?
David is unsure - whether to plough early
(Jun/Jul) and cause compaction/smearing,
or plough late (Oct) and bash the soil to a
seedbed because of baking. The long term
answer lies in drainage.
Brian Lawrence, farm manager, ‘Formosa’, Cressy
6-9% organic carbon and aims
to maintain it under lenghtening
cropping rotations with green
manure oats or annual ryegrass
➢ shallow surface drains
mainly alluvial black cracking clays (Canola) in
magnificent structural condition
➢ some Brumby and Brickendon with saline discharge areas
used for dryland cereals
Brian places great emphasis on very shallow surface drains that use the topography. These follow any
depressions on the gently undulating alluvial plain. They’re installed with a grader blade and
followed up after sowing with a spade to clean any lose soil from the bottom.
irrigated peas for seed and processing, green beans, poppies and Chinese cabbage. Dryland barley
and ryegrass seed grown with limited irrigation. Cropping rotations are lengthening, one paddock
appears to be in fine condition after 9 years cropping.
➢ the ryegrass seedcrop plays an important disease break and soil rejuvenation role in the rotation,
particularly as the rotation lengthens towards continuous cropping. It’s grown for 2 years and has
been sown up to the end of April on Formosa.
➢ Brian manages the rotation so that a maximum of two irrigated crops are grown before a dryland
cereal. The cereal really dries the soil, promoting deep cracking and mulching, an important
mechanism of structural rejuvenation for this soil type. Under continuous irrigated crops, the ground
never has a chance to really dry deeply.
Green manure
traditionally oats spread directly onto ungrazed stubble or the previous crop, followed by a shallow
discing. This has worked well, the only problems being slow germination and early growth, and some
grazing of the oats in wet conditions is bound to occur.
➢ this year the drill is being converted to allow direct drilling of annual ryegrass into the ungrazed
stubbles of all crops. The ryegrass will be irrigated for germination most years. After some grazing,
the ryegrass will be mouldboard ploughed under about May/June to allow winter self mulching before
final seedbed preparation.
Pushing the cropping rotation
Formosa soil tests show a healthy 6-9% organic carbon (or 15-19% loss on ignition), and Brian aims to
maintain these levels under long cropping rotations (8 years plus). He sees the following three
management points as very important;
a. No stocking in wet conditions , no wet tillage and avoid wet harvests if possible.
b. Have an oats or ryegrass green manure every winter.
c. Avoid long fallows - though they produce a good self mulch in the short term, in the long term organic
matter levels are declining. 3, 4 or 5 months of active crop growth per year is simply not enough to
maintain organic matter levels on an annual basis.
The mouldboard plough and roterra are used for all paddock preparations.
spread oats on surface, Jan
shallow disc
limited grazing in dry conditions
mouldboard plough, July/Aug
smudge if dry
sow poppies
Black cracking clays – sent to test our skills
Duplex soils
(sandy loam over clay) -
A significant area of Tasmania’s cropping soils are duplex. Duplex refers to the strong texture contrast between
the topsoil and subsoil. A uniform profile has no texture contrast and a gradational has moderate texture contrast.
Typical Brumby profile - from the midlands
Australian classification: Sodosol
Northcote classification: Duplex
Geology: Tertiary clay
Runoff: Moderately rapid
Drainage: Poor
Depth cm
Greyish brown to light brownish grey; fine sandy loam or loamy fine sand;
few to common yellowish brown mottles; weak structure; some profiles with
ironstone nodules; pH 6.0; salinity 0.1dS/m; abrupt wavy boundary;
Light olive brown to brown; medium clay; common yellowish brown and
common dark brown mottles; massive structure when moist, prismatic when
dry; sometimes with manganese concretions; pH 7.0; salinity 0.1dS/m; gradual smooth boundary
Olive brown; heavy clay to medium clay; common yellowish brown to red
mottles; structure massive (moist), blocky (dry), sometimes with manganese
concretions; pH 7.5; 0.2dS/m
Very dark greyish brown; loam or sandy loam; few yellowish brown mottles; weak subangular blocky structure; pH 5.5; salinity 0.1 dS/m; clear
smooth boundary;
Riversdale profile - from the Coal River Valley
Australian classification: Sodosol
Northcote classification: Duplex
Depth cm
Geology: Quaternary alluvium
Runoff: Rapid
Drainage: Imperfect
Black; sandy loam; weak fine (5-10mm) subangular blocky structure; few
very fine live roots; sharp smooth boundary;
Very dark brown; clay; very few fine faint dark reddish brown primary
mottles; weak medium (20-50mm) angular blocky structure; few very fine
live roots; abrupt smooth boundary;
Dark brown; clay; massive parting to weak medium (20-50mm) polyhedral
structure; few very fine live roots; clear (20-50mm) smooth boundary;
Dark yellowish brown; clay; massive parting to weak medium (20-50mm)
polyhedral structure; few faint clay skins very dark greyish brown coating
ped faces; few very fine live roots; clear smooth boundary;
Yellowish brown; clay; massive structure; no live roots;
Major challenges
- topworking takes care of paddock variation
How to crop these soils sustainability
paddock variability
wind erosion
maintaining organic matter
Capability and management depends on topsoil depth and texture. If there is less than 150mm (6”) of sand or
loam topsoil then the soil is unsuitable for intensive cropping which demands deep seedbeds and mouldboard
less than 100mm (4”)
more than 150mm (6”)
• cereals and fodder
• irrigated vegetables
peas, poppies, beans, onions
• cereals and fodder
• direct drill cereals
• topwork with tines or disc
Direct drilling
• cereals and fodder
• irrigated vegetables
peas, poppies, beans, onions
• irrigated root crops
potatoes, carrots, brassica
vegetables and seed crops in beds
• direct drill cereals
• topwork with tines or disc
• occasional shallow mouldboard
• retain residues and stubbles
• direct drill cereals
• topwork with tines or disc
• mouldboard ploughing
• green manuring
• retain residues and stubbles
Ploughing in stubble
DO NOT mouldboard plough areas at risk of wind erosion
topsoil depth does NOT include the bleached A2 subsoil layer
Regions and local names
Most of Tasmania’s arable soils are duplex. Extensive areas occur in the Midlands (Brumby, Woodstock,
Brickendon, Newham) and Coal River Valley (Apricot, Richmond, Bridge, Riversdale, Coal, Strelly,
Carrington, Nugent, Southfork, Enfield, Daisy) as well as the East Coast, the Meander and Derwent
Extensive on tertiary sediments, often with surface deposits of windblown sands as dunes or thin sheets.
Commonly occur in conjunction with heavy, black cracking clays which follow natural drainage lines or
the present floodplain. Land capability of duplex soil areas is 4 or less depending on limitations such as
depth, wetness and slope.
Key properties of duplex soils
Paddock variability
High. Topsoil depth and texture varies greatly across the paddock depending on accumulation of
windblown sands. Depth and texture determine management practices. The whole paddock must
be managed to avoid wind erosion of the sandy areas.
Commonly wavy. To determine topsoil depth, don’t rely on just one or two holes.
Low. Impermeable clay B horizon causes waterlogging. Options for improvement are limited.
Concentrate on surface drains, maintaining organic matter levels and avoiding compaction of
pores in the subsoil clay.
Organic carbon
Low to medium contents in the A1 (about 2% for a sandy loam), dropping sharply very low
levels (0.2%) in the A2 and negligible levels in the clay subsoils. Decline is rapid under conventional cropping.
Root growth
Restricted. Very few roots extend into the A2 or clay B horizons because of poor fertility and
Readily available
Low. About 25mm in 200mm depth of sandy loam topsoil. Shallow topsoil and restricted rooting
into the A2 and B layers mean crops quickly move from waterlogged conditions to drought
conditions. Irrigation is required in frequent small volume applications.
Moderate. Commonly restricted by waterlogging in autumn, water and spring. Low where the
sandy A horizon is thin. Heavy traffic or tillage operations in wet conditions compacts the clay B
horizon. These soils are easily overworked to a powdery tilth.
Low. Topsoils have low total nitrogen contents, medium to low total phosphorus and low available potassium.
Moderately to strongly acid topsoils, (pH 5-6). pH increases with depth becoming alkaline in
the lower profile (<1m).
Low to high. Less than 0.2 dS/m, generally increasing with depth, many subsoils being slightly
saline at greater than 50cm depth. Highly saline scald areas are commonly associated with
drainage lines or toeslops.
Slight to moderate in upper B horizon, increasing with depth, especially the Brumby Association. Dispersion and slow permeability are problems associated with sodicity.
Erosion risk
High. Thin, light textured topsoils are susceptible to wind and water erosion if overworked and
Variable. Common problem for small seeds like poppies.
Rocks and stones
Usually none but sometimes have alluvial waterworn remnants, or ironstone deposits as gravels,
rocks or large slabs
How much cropping can duplex soils take
The pasture phase is critical. In higher rainfall areas where pasture growth is more vigorous and less
susceptible to root feeding grubs, longer cropping rotations can be supported. A run out pasture puts
nothing into the soil and fertility and organic matter levels decline. For more intensive cropping, short
term ryegrass (8 months to 2 years), provides the option of shortening the rotation to say 2 or 3 years
crop between pastures, particularly if the pasture is irrigated.
Under conventional cultivation involving stubble grazing/baling and mouldboard ploughing, a
rotation with about 2 years of crop in 10 is considered sustainable.
Under direct drilling or topworking with stubble retention or shallow incorporation, and surface
drainage, perhaps 5 to 6 years of irrigated and cereal crops can be grown in 10 years.
Under dryland cereal/legume rotation with minimal grazing of stubbles and direct drilling,
continuous cropping may be sustainable.
Is ripping appropriate?
of the topsoil - a shallow ripping may be appropriate
after compaction as part of a topworking tillage
of the A2 horizon - is pointless. The sodic nature of
this spewey layer means it will collapse to its original
state during the first wetting after ripping
of the clay subsoil - is also pointless. The overlying
sodic A2 will flow into and block any cracks and voids
created by the ripping operation.
Are powered implements appropriate?
These soils are very fragile. Structure is minimal and is
maintained only by the presence of roots and organic
matter. Powered implements are not necessary, but can be
used with care for shallow workings at the right moisture
content. Use a low rotor speed and high forward speed.
Some models allow opening of rear shutters to minimise
pulverisation. A good seedbed is best prepared using tines
and/or discs.
An overworked duplex soil with lumps of
subsoil clay mixed in the topsoil causing
crusting and poor infiltration.
Can I deepen by topsoil?
Yes, but at the expense of fertility, structure and erodibility. The underlying pale A2 layer is acid,
structureless and often sodic. Mixing in a little over time will gradually degrade your topsoil.
What NOT to do!
mouldboard plough paddocks at risk
of wind erosion
do not plough or mix in the A2 layer
deep rip below the topsoil
Topworking is best for duplex soils
Management Guidelines for Duplex Soils
Management depends on topsoil depth and wind erosion risk.
cereals and fodder only
Soil management
direct drill
Topsoil less than 100mm (4")
Topsoil 100-150mm (4"-6")
cereals and fodder
➢ direct drill
➢ peas, poppies, beans, onions ➢ topwork with tines and discs
Topsoil greater than 150mm (6")
occasional mouldboard plough#
cereals and fodder
➢ direct drill
➢ peas, poppies, beans, onions ➢ topwork with tines and discs
NOT potatoes
potatoes, crops in beds
mouldboard plough#
provided there is NO RISK OF WIND EROSION
Prevent wind erosion. Do NOT mouldboard plough sandy duplex soils at risk of wind erosion.
Topwork with tines or discs. Topworking retains turf and crop stubbles on the surface between crops.
Avoid overworking. Duplex soils are fragile . Use of powered implements requires skill and
judgement. Deep mixing and stirring rapidly destroys structure and fertility.
Do NOT plough shallow duplex soils. Most duplex soils are too shallow for mouldboard ploughing
(100mm or 4 inches of topsoil is minimum). Gradual mixing of the bleached A2 layer, or worse still,
the brown subsoil clay, with your topsoil will degrade longterm structure and fertility.
Promote surface drainage - for undulating paddocks, open up drainage lines linking hollows and
depressions with broad shall grassed ditches. Leave these unploughed during cropping. In flatter
paddocks, plant up and down slope.
Retain and/or incorporate all stubbles and residues. Your efforts will be rewarded. If you wish to
incorporate large amounts of organic matter, use the mouldboard plough rather than a powered
implement provided topsoil is deep enough.
Adopt direct drilling techniques. Developing techniques for potatoes and poppies is a top priority
since these crops cause the most erosion. Ask field officers for advice.
Avoid compaction and pugging. Assess subsoil moisture before ploughing, working or harvesting.
Grazing oats, rape or turnips in wet conditions is a sure way of destroying your cropping soil.
Duplex Soil Case Studies
Andrew Bond, ‘Eastfield’, Cressy
Brumby/Panshanger sand complex of deep sandy banks
and shallow duplex hollows
➢ Woodstock on higher terraces, (shallow duplex with
ironstone gravel)
➢ Eastfield, stony dolerite soil, too stony for cropping
➢ Cressy shaley clay loam and Kinburn.
surface drainage for duplex soils
long pasture phase
heavy duty S tine implement
Andrew grows higher value crops between long
pasture phases of about 10 years duration. Cropping
phase varies from 2 years on the shallow Woodstock
soil to 5-6 years on the better Cressy and Brumby/
Panshanger soils
crops include potatoes, beans, poppies, onions and
some barley and peas.
Organic matter management
Being in a higher rainfall area of the midlands, Andrew can
sustain productive and vigorous pastures for up to 10 years.
Such long pasture phase builds soil organic matter and
structure sufficiently to last through the cropping phase
without green manure crops or incorporating large amounts
of stubbles/residues. Stubbles/residues are rarely burnt,
usually baled and grazed to a point where subsequent
tillage is not inhibited but erosion is avoided.
Andrew uses the mouldboard plough to bring a paddock
out of pasture, and uses a heavy s-tine cultivator and
roterra between crops.
Andrew inspecting topworked onion seeedbed
Mouldboard plough
S tine or roterra
sow barley
1995 onion preparation on Panshanger sand/Brumby at high risk of wind erosion;
direct drill oats after harvest
sprayed off oats
leave for 2 weeks
heavy S tine x2
shallow roterra
sow onions
Topworking is best for duplex soils
Surface Drainage
Waterlogging in the hollows is a major limitation to cropping Brumby/Panshanger complex soils. After
surveying the paddock if necessary,
natural drainage lines are linked with
broad shallow permanently grassed
drains, constructed with a road grader,
laser guided if fall is minimal. It is
important to grade spoil well away so
crop rows have a continuous fall off
the banks all the way to these drains.
To avoid excessively deep surface
drains, some hollows are drained with
underground pipe and sump structures.
Shallow surface drains on Eastfield.
Andrew has sumps and underground
pipe where necessary.
Andrew Youl, Symmons Plains, Epping Forest
one pass powered implement
for all preparations
Main cropped soil is Brumby which varies across the
paddock, the banks being deep sand to the hollows where clay comes to within a few inches of the
Other less fertile uncropped duplex soils include Brickendon with Newham foot slopes, the Newham
containing saline scald areas, and Woodstock shallow ironstone gravel country usually left in native
bush or developed into a pasture.
An impressive range of crops have been grown at various times on Symmons Plains;
Canary seed
Sweet corn
Clover seed
Pak choi
Chinese cabbages
Generally alternate with a cereal in between each crop,
the rotation continued until the decline in soil quality
begins to lower yield.
Paddock preparation for all crops is now achieved
with a single pass Kuhn operation (spikes rotating
on a horizontal shaft, followed by a solid toothed
➢ major advantages are excellent timing of tillage to
soil moisture conditions due to high work rate and
single pass. Other advantages are listed on page 49.
Work rate
24ha (60 acres) per 8 hour day
4m (13 feet)
Tractor power 190kW (250hp)
Capital cost
Other features: adjustable rear flap to vary
degree of working, solid toothed roller to take
implement weight during work.
Problems: supposed to produce an even, firm
seedbed but soil builds up around the roller teeth
leaving slight ridges
Planned addition will be ripping tines to the front of the machine, not so much to alleviate deep
compaction, but to loosen topsoil before it passes through the spikes, particularly after grazing. This
will reduce load on the machine.
➢ various tillage systems have been tried on Symmons Plains but not continued. These include
mouldboard ploughing and tined secondary passes, (discontinued because of slow work rates and
excessive number of passes), and chisel ploughing.
even incorporation of crop residues
➢ disintegrates clods
chops crop residues
➢ mixes residues and clods throughout topsoil
no secondary tillage wheelings
➢ adjustable rear flap varies degree of
Powered implements and duplex soils
Duplex soils are structurally weak. Overworking the soil is very likely
using a powered implement. Overworking develops a soil with problems
such as poor aeration and drainage, clods and powder seedbed, crusting
and wind erosion. The many advantages of the powered implement are
soon lost unless its operated with a high level of skill, care and judgement.
Topworking is best for duplex soils
PJ & NJ Chilvers, ‘Winburn’, Nile
The Chilvers family farm about 800ha at Nile in the North
midlands, with various stock and crop enterprises. Cereals (oats,
wheat & barley), grey peas and irrigated processing peas and
poppies are grown every year. Green beans have also been grown.
Main Points
topworking & direct drilling
no powered implements
stubble grazing avoided
prior to direct drilling
mainly duplex (Brumby Association) overlain with windblown sands, sometimes as a thin sheet and
sometimes as small dunes.
➢ some recent alluvial soils varying from black cracking clay to stoney loams associated with the Nile
➢ black cracking clay (Canola Association) varying from
very poor to very well structured
a third to half the arable area is cropped in any one year.
perennial pastures (ryegrass, Cocksfoot, Phalaris and
clovers) are sown and usually remain productive for 4-6
years before sucuming to pasture grub infestation.
➢ a cropping rotation on better duplex paddocks usually
consists of peas or poppies / cereal / cereal / peas / cereal
Green Manure
Oats are sometimes direct drilled into mulched poppy, pea or
cereal stubble. Volunteer seed from previous crop and the
oats all germinate and provide growth for winter grazing.
Stock are taken off during wet weather to keep compaction to
a minimum. Oats are mouldboard ploughed prior to peas.
Primary Cultivation
crops are preferably direct drilled or sown into
‘topworked’ seedbed (shallow discs and tines).
Mouldboard plough preparation is used only for
processing peas.
➢ it is observed the soil remains in
better condition under ‘topworking’/
direct drilling, particularly if the
season allows the stock to be kept off
the cropping paddocks. The topsoil
structure remains friable, open and
full of continuous pores that go down
into the subsoil, enabling a longer
cropping rotation.
➢ No powered implements are used,
though at times the Chilver’s have
been tempted to try one on their
poorly structured black soil (clods).
A stiff tined cultivator is used on
occasions for weed control in long
Excellent soil structure after
incorporating pea stubble.
Stubble mulching plays an integral part of the
Chilvers’s topworking and direct drilling program.
Secondary Cultivation
the S tine with front levelling boards and double crumble
rollers behind is a key implement used for all seedbed
preparations. (Front cover photo.)
➢ a Nobili flail mulcher is used on stubbles, two passes for
heavy stubbles, breaking straw into 20cm or less lengths.
This improves trash flow and speeds biological
breakdown for direct drilling or mouldboard ploughing
Direct drill barley in barley stubble yielded the
same as an adjacent paddock conventionally
worked and sown the same time.
an example of soil management between wheat and peas ’94/
’95, taking advantage of that years summer rainfall by direct
drilling oats for grazing.
flail mulch x 2
direct drill oats
mouldboard plough Sept
S tine
sow peas
direct drilling cereal, no winter grazing
flail mulch x 1 or 2
shallow disc x 1 or 2
allow winter regrowth
direct drill
topworking poppy preparation, avoiding soil crusting and wind erosion
spray off Aug
shallow disc twice
scarify to obtain even seedbed depth
drop seed on surface (late Aug)
Topworking is best for duplex soils
Deep Sands
General description
Deep (>70cm, 28") uniform sandy profiles characterised by
topsoils ranging from reddish brown to greyish brown.
Topsoils show a slight accumulation of organic matter and
weak structure.
wind erosion
waterlogging hollows
maintaining organic matter
Regions and local names
Deep sands are not extensive, they occur as coastal deposits along the state’s North coast, and as
windblown deposites known as Panshanger in the Midlands, and Invequarity, Penrise and Pines in the
Coal River valley.
Being windblown deposits, these soils are notoriously variable in depth and occurrence across any one
paddock. They may occur as deep dunes or as a sheet of varying thickness deposited over the top of older
soils. In other areas, where sands have been blown over dolerite hills, outcrops and floaters of dolerite
bedrock may be common in the profile. Land capability is typically 4.
Key properties of deep sand soils
Rapid. However, waterlogging occurs in hollows where underlying clay approaches the surface.
Root growth
Unrestricted. No inherent physical barriers to maximum potential rooting depth. Compaction by
tillage, traffic or stock can pack sand grains together and restrict root growth. Hard pan below
tillage depth can form.
Readily available
Low. About 30mm in 300mm of topsoil depth. Irrigation is required as frequent small
volume applications.
High. No moisture restriction on tillage operations. Easily overworked.
Organic matter
Low. 0.5-1.5% organic carbon in the topsoil.
Poor. Plant nutrients supplied almost entirely from organic matter. Applied nutrients easily
leached, particularly if organic matter levels are depleted. Low in total nitogen and available
potassium. Available phosphorous low to medium in topsoil.
Slightly acid, becoming neutral to slightly alkaline with depth. Low buffering capacity.
None. Saline seeps may occur at the edge of dunes where they overlie a clay substrate.
Erosion risk
High. Sandy texture, weak structure and loose consistence make these soils highly prone to wind
and water erosion.
Water repellence
Variable. Not necessarily related to depleted organic matter levels. Humic substances coating
sand grains can be non-wetting.
Surface crusting
Variable. More likely if coarse organic matter is depleted by initial mouldboard ploughing out of
pasture or by several years of cropping. A problem for germination of small seeed crops like
Rocks & stones
Outcrops may occur in sands deposited on dolerite hills.
- easy to work, easy to lose
Typical Panshanger sand - from the midlands
Australian classification: Tenosol
Northcote classification: Uniform
Major challenges
Geology: Windblown sand
Runoff: Moderate
wind erosion
waterlogging hollows
maintaining organic matter
Drainage: Rapid
Depth cm
Very dark greyish brown sand to loamy sand; single grained or fine
(5 - 10 mm) subangular blocky structure; loose or very weak consistence;
common fine roots; field pH 5.8; clear smooth boundary
Strong brown to dark yellowish brown; sand to loamy sand; some profiles
may have a few grey or brown mottles; single grained or massive structure; few
fine roots; field pH 6.7; gradual smooth boundary
Strong brown to yellowish brown; loamy sand; single grained or massive
structure; few clay coatings and a few manganiferous soft segregations in some
profiles; very few fine roots; field pH 7.0; gradual smooth boundary
75 +
Variable yellowish brown colours, may be mottled; sand to loamy sand but
some clay horizons; single grained or
massive structure;
Direct drilling potatoes into ripped, dessicated pasture
A direct drilled poppy
emerging through cereal stubble
Wind erosion at Wesley Vale
Management Guidelines for
Sandy Soils
1. Retain a cover on the
surface at all times. About
1.5 to 2t/ha of stubble
provides sufficient protection
against wind erosion. Sow a
cover crop.
2. Never mouldboard plough.
Inversion maximises wind
erosion risk.
3. Adopt direct drilling
techniques, minimum tillage
or topwork with tines or
A dam-a-dyker creates small basins to encourage storage and infiltration
of rainfall and irrigation. Ideal for potatoes and crops in beds.
4. Powered implements are not appropriate for
sandy soils. Wind erosion risk is increased and
loss of humus is maximised.
5. Leave high risk sandy banks out of crop
6. Irrigate frequently with small volume
Mouldboard plough preparation for potatoes
maximises risk of wind erosion.
Deep sand case studies
Dennis Creese/Simplot partnership, ‘Brambletye’, Conara
Growing potatoes in sands is sustainable only
if wind erosion is avoided. The only way to
avoid erosion is to keep sufficient coarse
organic matter on the surface of the mould.
keep some turf or straw in the mould
use a disc & rip preparation
NO mouldboard ploughing
spray off, 1st week Sep
disc x2, 2 wks before planting
rip, 300mm (12")
plant, end Oct
Only if turf is excessive, an additional roterra pass 150mm (6”) is included before planting.
Consider also a pasture/oat preparation being used by Simplot in the far North East of the state.
spray off, Mar
disc x2
sow oats Apr
rip, 300mm (12") Sep
roterra, 150mm (6")
For potato preparation in sands:
two shallow discings will leave the most
organic matter in the mould for erosion
control. For highly erodible paddocks this
is best.
a deep pass with a powered implement is a
second preference. The powered
implement results in the mould containing
pieces of organic matter evenly mixed
the plough should not be considered for
sandy soils because it buries organic
material below the depth of moulding.
Mouldboard ploughing maximises erosion
Striking a balance
Disc and rip preparation has left plenty of turf
in these moulds. Highly resistent to erosion.
Brambletye, December 1995.
While producing a mould with sufficient organic
matterial for erosion control is a must, too much
organic material as lumps of turf tends to cause
uneven moisture within the mould, excessive
moisture loss and more manual workload during
harvest. But erosion control comes first.
Sandy soils – easy to work, easy to lose
Ian MacKinnon, Glen Esk & Snaresbrook, Conara
Dryland cereals, grain legumes and lupins
high wind erosion risk
direct drilling primarily
for economic reasons
lucerne pasture
mainly duplex (Brumby) overlain with windblown sands
(Pansanger) of varying depths from sheets to dunes
the deeper sands tend to be odd shaped areas within
paddocks so the whole paddock has to be treated with
extreme care
aims for 9-10 year rotation similar to that followed in the
Australian wheat belt, however, finding a reliable and
profitable legume for the rotation remains a problem.
Lupins and various grain legumes have been tried.
1st year
*used for grazing
Ian’s manager takes a close look at seed
placement. “If conditions are not right, you
have to be prepared to wait.” Judging seed
depth, press wheel pressure and soil moisture
are key decisions in the success of direct drilling.
Traditional tillage
heavily graze with sheep
off set disc 2-3 passes
heavily graze with sheep
leave over autumn
burn off herbicide - June/July
direct drill
Minimum tillage
Ian still likes to off-set disc out of pasture in Autumn and sow oats in April. He has converted an
International 6-2 drill for direct drilling, used successfully with cereals, legumes and lucerne.
Making money is the main reason for direct drilling. Sustainability and the Landcare ethic are very much
secondary benefits.
Rob Morey, ‘Flexmore Park’, Penna
➢ rip, plant and pre-emergant burn off
➢ cereal broadcast prior to harvest
➢ lucerne based pasture
crops 200-300 acres of deep windblown sand
crops only 2 years (barley, potatoes), followed by a 12 month fodder crop, before returning to a long
lucerne based pasture.
Rob never mouldboard ploughs because of the erosion hazard.
spray off during active growth
(Glyphosate & Dicamba)
sow barley
Lucerne must be sprayed 6-12 months to achieve root breakdown prior to ripping and potato planting to
avoid machine blockage and harvesting problems. Rob grows a barley crop during this time.
allow regrowth weed & grain
deep rip
plant potatoes August
pre emengent burn off herbicide, Sep
broadcast cereal seed immediately prior to
potato harvest
harvest potatoes
*oats/rape or barley/rape mix for 12 month grazing
heavily graze stubble, autumn
direct drill cereal cover crop
direct drill lucerne 2 weeks later
Sandy soils – easy to work, easy to lose
Diagnosing your drainage problem is the key to achieving success with
any drainage solution. You need to know the source of the water and
where it is moving in the soil. This will ensure correct selection of drain
depth and position.
Remember investigate and plan for
drainage in winter, install
in summer.
The layout of both surface and subsurface drainage must be considered early in the planning process. The
location of surface drains will influence the location of fences, shelterbelts, laneways and the shape of
The most satisfactory way of doing this is with an aerial
photograph of the farm enlarged to an appropriate scale.
This service is available from the Land Information
Bureau, GPO Box 44A, Hobart (Ph 03 62 338011). The
photograph allows you to record the extent of problem
areas, where drains are to be installed, and estimate
distances and costs involved.
When to investigate, when to install
During winter, a couple of days after a good soaking rain,
is the best time to take a closer look your wet area. You can
identify the extent of wet areas and identify soil layers on
which a perched water table occurs.
Take a spade or auger and dig a series of small pits or holes
up to 1 m deep in and around wet areas. Use pegs to mark
out drainage lines and potential drain locations. Summer
and autumn are the best times to install drains. This is when
soils are dry and have their greatest bearing capacity for
supporting heavy construction machinery. Machines won’t
become bogged and trench sides smeared.
What to look for when digging your pits:
Dig or auger holes down into the subsoil
Do your holes fill with water
∗ Soil colours. Paler, bluer colours indicate poor drainage.
from the bottom - even slowly?
Mottles are spots, blotches or streaks of subdominant colours
➢ yes, deep open surface
different from the main soil colour.
drains or subsurface drain∗ Where does the water flow into the pit from ?
age is a solution
- from the bottom; indicates a ground water problem
➢ no, options are limited to
- from a particular layer; indicates perched water
land forming or shallow
- from the surface; indicates surface sealing or perching.
surface drains
∗ Layers of contrasting texture or hardness, eg. sand over clay,
lenses of sand, or hard pans. These will result in perching and will
require placement of drains at a specific depth. If water perches near the soil surface on a particular layer,
there is only limited potential for significantly improving drainage.
∗ Hard concretions of various sizes and shapes or soft black segregations often indicate poor drainage.
These are composed of iron and/or manganese. In extreme cases these can form thick impenetrable
ironstone or “coffee rock” on which water now perches.
Good soil management begins with good drainage
Keen to tackle that wet area?
Ask your local DPIF office for a copy of The Drainage
Manual, a helpful booklet and audio cassette tape on
drainage planning and installation.
Signs of poor drainage• Pale colours
• Red-stained root channels
• Mottles
How much fall should a surface drain have?
A minimum of 0.3% (30cm in 100 m)
Erosion is likely where fall is greater than 1% (1 m in 100 m)
for duplex or sandy soils, or 5% (5 m in 100 m) for krasnozem, Cressy and black cracking clay soils.
Successfully removing a seep like this one with sub-surface
drainage often requires several attempts. Improve your
chances by placing a few investigative open drains into the
seepage area a year before and observing water movement
over the winter.
Thinking of subsurface drainage?
Always explore and implement surface drainage options first,
especially in duplex soils.
Milky puddles and slumping structure indicate
unstable soil, not suitable for mole drains.
“I’ve found shallow land planing (+/-5 cm), has
reduced the effects of winter waterlogging on my
duplex soils.”
Jim Taylor - Nile.
Use the topography.
Join depressions and hollows with shallow surface drains
for waterlogging in black cracking clays, Cressy and
duplex soils.
Excess Rainfall &
no infiltration
Divert excess water while it’s on the surface
whenever possible rather than allow water
to run and fill low lying areas.
Ponding or erosion
Infiltration restricted by poor soil structure, silty
texture or non-wetting organic matter
Divert surface water from entering the area
Control and direct runoff without erosion
Perched watertable on clay subsoil of duplex
The extent to which this land can be improved by
drainage is limited, no matter how much you
Ponding on flat areas
➢ cut-off drain (20-40cm)
➢ land levelling
➢ beds or moulds (20cm)
➢ hump and hollow
➢ mouldboard bedding
divert runoff from entering the area
surface drains linking hollows
strategic subsurface with sumps
gravel moles
seek professional advice
Erosion on steep areas
➢ cut-off drains
➢ grassed waterways (10cm)
➢ grassed irrigator lanes
➢ contour drains (10-15cm)
➢ diversion banks 20-50cm)
➢ cover crops/stubble retention
➢ topworking
Link hollows and depressions with surface drains.
Water infiltrates, hits deep impermeable layer and
moves along it to resurface some distance
Regional watertable associated with floodpain
Controlling the height of the table can produce
first rate cropping soils
Deep seepage intercept drain (70-120cm)
in the form of;
➢ open ditch
➢ French (stoned) drain
➢ subsurface pipe and gravel backfill
seek professional advice
open arterial drains (100-200cm),
depth and spacing depend on soil
permeability and presence of
underlying gravel layers
seek professional advice
improved land
Place surface or subsurface
intercept drain here
Infiltration &
deep drainage
Wet area
Impermeable layer
A pumped drainage scheme near Bishopsbourne
Place intercept drain upslope where watertable is at
least 450mm (18”) below the surface. Ensure drain is
dug into underlying impermeable layer.
Surface or subsurface drains?
Surface drains are a minimal investment (say $2/m), last a long time provided
stock are excluded and can always be deepened or moved. Subsurface
drainage schemes are only warranted for intensive cropping or dairying farms.
Strategic subsurface drains that use the topography may be worthwhile for less
intensive farms. Large amounts of money are literally sunk in subsurface
drainage ($5-10/m) - if it’s right, that’s fine, but if it doesn’t work......
Tips on surface drains
What is the most
common cause of
subsurface drainage
Blocked or damaged
install in dry conditions and use a dumpy level if necessary
a minimum fall of 0.3% or 30cm in 100m for a surface drain requires regular maintenance, especially
vegetation and stock exclusion. A two wire electric fence is all thats required for trained stock.
Trenchless machine
Mole plough
Tips for subsurface drains
install in dry conditions. A trenchless machine should create lots of soil heave as it passes, rather than
smearing and compaction of trench sides.
➢ mole drain in spring when the subsoil is moist and topsoil dry. A small bulldozer is best.
➢ check relative depths of gravel backfill and mole channel to ensure the two connect.
Drainage by soil type
The table below is a guide to drainage problems and solutions for various soil types. Specific sites will
vary in their requirements.
Black cracking
clay- hills
Black cracking
clay - alluvial
erosion &
cut off drain
grassed waterway
grassed irrigator run
and contour drains
seepage intercept
deep arterial
strategic* subsurface
strategic shallow surface
grid subsurface
mole channels
*strategic drains target particular areas of the paddock as opposed to a grid drainage scheme involving evenly spaced parallel
drains across the whole paddock.
Sodic soils
What is a sodic soil?
Take a crumb of suspect soil and drop it into a glass of pure rainwater. Watch how it breaks down over
the next 12 hours. Most clays slake, this is normal. But some clays disperse, these we call sodic clays.
Slaking. Fragments flake off the soil crumb due to pressures that build
up as water forces air to escape during the wetting process. Most clay
soils will slake when wetted, particularly after a long dry period. This
is not a sodic clay.
Dispersion. If you drop a lump of sodic clay into a glass of fresh water,
the water gradually goes cloudy. A muddy halo forms if the sample
isn’t shaken at all. This is a sodic clay.
Do you have a sodic soil and where is the sodicity occurring in the
profile? These are the first steps of investigation.
Where do they occur?
Duplex soil drainage line.
Middle dish shows dispersive
layer in the soil.
About a third of Australia’s soils are sodic.
Brumby, Newham, Brickendon and Woodstock are soils of the
Midlands likely to be sodic to some
degree. Some black cracking clays are
In Tasmania,
also sodic. Most sodic soils in
soils are
Tasmania are classified as moderately
associated with
sodic or less.
many duplex
(sand over clay)
What part of the profile?
soils through the
Sodic soils are highly variable in terms
Midlands, Coal
of where in the profile the sodicity
River and
occurs and the degree of sodicity.
Flinders Island.
Boundary Horizon
Sandy loam or san
Pale spewy layer
sodic region
brown heavy clay
This diagram shows how sodicity commonly occurs in the A2 and upper B layers
of a duplex profile.
What is the problem with sodic soils?
Overcoming waterlogging. Existing cracks and fissures in the subsoil offering drainage of excess water
from the topsoil, are blocked off by the unstable sodic layer which flows and chokes these channels
during waterlogged conditions.
Management of sodic soils under cropping
There are two basic approaches, both involving drainage;
1. Good soil management - drainage (strategic underground or surface), increase organic matter inputs,
avoid compaction and adopt minimum tillage/direct drill cropping program.
➢ no risk of failure
➢ low cost, long term improvement
➢ appropriate for dryland cereals or
occasional irrigation (peas/poppies)
2. Reduce sodicity - involves applying
gypsum (contains calcium) combined
with drainage (to leach sodium
chloride out of the clay)
➢ high risk, try a small area first
➢ will not work if poor soil
management practices continue
➢ high cost, bulk gypsum costs at least
$70/tonne ex Railton
(apply at 2-5t/ha)
➢ short term, unless gypsum application
is continued, tillage intensity is reduced and organic matter inputs are increased
➢ appropriate for more intensive cash cropping/high return situation
For undulating paddocks, a combination of the above may prove most effective and economic. The
whole paddock receives good soil management practices, with severely waterlogged depressions and
drainage lines being linked with underground drains and treated with gypsum.
Flatter paddocks with extensive areas of shallow sodic soils, are best managed using option 1. ie good soil
management practices, where slight improvements in soil condition can be expected year by year.
Intensive drainage and gypsum treatments are unlikely to improve the paddock greatly, let alone pay the
Deep Tillage and sodic soils
Deep ripping disrupts existing pores in subsoil layers and aggrevates the unstable nature of sodic layers.
The soil collapses to its original condition as soon as the profile becomes waterlogged again.
Mole drainage and sodic soils
If the duplex soil has a distinct pale A2 layer, this may flow into the mole and cause failure, even if it’s
not sodic. Risk of initiating tunnel erosion if there is some slope.
Further reading
Sodic Soils – A Review, Jayawarade, N.S. & Chanky.
Aust. J. Soil Res; 1994, 32, 12-44.
The Distribution of Sodic Soils in Tasmania, Doyle, R.B. & Habraken, F.M.
Aust. J. Soil Res; 1993, 31, 931-47.
Introduction to Soil Sodicity, Cooperative Research Centre for Soil and Land Management.
Technical Note No. 1, June 1994.
Cover cropping
In the future, cover crops are set to play an increasing role in the growing of clean, green produce. The
Tasmanian DPIF conducted very encouraging trials in 1994/5 using a ryecorn cover for brassicas planted
as speedlings. The ryecorn cover was allowed to reach about 600mm high before spraying off with
glyphosate two weeks before planting. Not a single herbicide spray was required during the life of the
crop and soil losses were negligible. The main barrier to wider adoption of sowing into cover crops is
that modification of the drill is required for added trash clearance.
Apart from some oat cover crops for lettuces in the Coal River valley, onions are the only commercial
annual crop commonly grown with a cover.
What are the benefits?
flexibility, being a short term ‘crop’ as opposed to shelterbelts or other more permanent barriers
low cost
complete protection across a paddock. The benefit of shelterbelts or corn shelter rows diminishes with
➢ adds to soil structure and biological activity, a living mulch
➢ smothering of weeds, reducing or removing the need for herbicides
Cover crops for onions
Two ways of growing a cover crop for onions
sow cover before onions and burn off just prior to
onion emergence using non-selective herbicides.
sow cover and onions together, and burn off about
three weeks after onion emergence using selective herbicides.
This method is most commonly used at present.
The herbicides
These are divided into Selective and Non-selective (against
Your agronomist may use low rates with the aim of slowing
but not killing off the cover. The life and benefits of the
cover are prolonged, while competition with the onions is
It all depends on the weather!
The timing of herbicide application requires an experienced
agronomist considering the 3-4 week delay between burn-off
Oat cover crop for onion, Wesley Vale, July 1995
application and cover crop dessication.
Also, oat growth is affected by warm and cold weather more
than onion growth. Warm weather - oats grow faster than
onions. Cold weather - oat growth slows dramatically while
onions keep growing.
Sow cover before onions - two examples
University Farm, Cambridge, sandy loam over clay, 1-3% slope
Reason for sowing cover is to reduce wind blasting of emerging onions and some erosion control. In
addition, several contour drains were installed to reduce erosion risk using an old single furrow plough.
Oats were used at the usual rate of 30kg/ha.
University farm program 1994/5
Oat cover
Day 1
Day 10
Day 21
Day 47
Day 60?
4-5 leaf stage*
almost emerged
4 leaf
non selective
*Non selective applied just prior to onion emergence a kill of all weeds and hoping some oats would survive and shoot again to
provide continued protection.
Timing of herbicide application depends on temperature, moisture and sunshine hours. Seek professional advice.
University farm program 1995/6 Triticale cover
Day 1
Day 10
Day 21
Day 45
2-3 leaf stage*
5 leaf stage
almost emerged
3 leaf
Timing of herbicide application depends on temperature, moisture and sunshine hours. Seek professional advice.
*Roundup @1.5l/ha just prior to onion emergence or up to 3 weeks (for root release) prior to sowing if using a precision drill
which requires a trash free seedbed
Sow cover & onions together - an example
Roberts Vegetables Pty Ltd and Nigel Wade, Table Cape 1995/96
A krasnozem soil containing ironstone gravel. The gravel is picked up by the wind and knocks the waxy
outer coating off the onion plants. With a damaged coating the onions are no longer protected against
selective herbicides.
10 May
11 May
26 June
Week 7
graze stubble
oats spun onto stubble
Roterra/crumble roller
4-5 leaf stage
starting to tiller
onions sown
*knock back oat growth only
**kill off oats
almost emerged
flag leaf stage
pre emergent*
Competitive effects of cereal cover
A vigorously growing cereal will compete for moisture during onion germination and early growth.
In drier regions like the Midlands or Coal River, spraying off the cereal before onion sowing may be
the best option.
Once the cereal is sprayed, growth and uptake of moisture and nutrients ceases, even though the
herbicide may take 3 to 4 weeks to kill the cereal cover. The only competition after spraying is
Triticale - an alternative to oats
Triticale is more upstanding than oats, allowing more herbicide to reach other weeds
Oats are more substantial plants due to tillering at such low plant density. This makes the cover more
difficult to kill off.
Retaining cereal stubble - an
alternative to a cover crop.
A cereal stubble is well worth considering:
provides cover pre- and post-onion
no competition with the onion crop
no critical timing of herbicide
but what are the problems ?
a stubble’s challenges lie in tillage (type
of implements, timing, depth and speed
of work). There are small seed drills
that handle a reasonable amount of
stubble. One example is the Accord
airseeder, used by Ron & Chris Gunn of
Richmond to sow into barley stubble
after some grazing and discing.
excessive stubble can affect
germination of small seeds like onions
A retained stubble has no competitive effects
or herbicide requirements.
Direct drilling & locally converted drills
Benefits of direct drilling
Crop stubbles were traditionally seen as a
problem and a good farmer was one who
managed to remove by grazing, burning
and ploughing every last remnant of the
previous crop’s residue. Today, farmers
are beginning to see stubbles as a resource. Adopting new technology and
modifying old machinery allows effective
use of the resource to bring a wide range
of benefits.
A converted drill in NSW with press wheels.
reduced soil erosion by wind and water
saving up to 75% in tractor fuel consumption
long term soil structural maintenance or improvement
improved soil nutrient and water holding capacity
improved soil biological activity and cycling
Which soils are appropriate?
All soil types. For deep sands and duplex soils, the chief benefits are control of wind erosion and preservation of structure. For clay soils, which require expensive cultivation to prepare, the benefit lies in
lower costs. For all soil types, fertility largely depends on the soil’s organic matter level, and experience
has shown the levels usually improve under direct drilling.
Direct drilling clayey soils (krasnozem, Cressy & black cracking)
Under direct drilling a clay soil may either improve or deteriorate, depending on management. Under
poor management, compaction increases year by year. Under good management, the crumb structure or
natural tilth of the surface layers improves, largely because of the gradual increase in organic matter in
the top few centimetres of soil. Biological activity in the topsoil improves porosity and structural stability,
and a beneficial organic cycle is developed.
Factors influencing soil condition trend under minimum cultivation for clayey soil.
unstable soil type
poor drainage
late drilling
unnecessary traffic
poor weed control
excessive surface trash
prolonged wet weather
Present state
self mulching soil type
good drainage
winter cropping
timely drilling
minimum traffic
tramlines (controlled) traffic
dry weather and frosts
from Soil Management, Fifth Ed, Davies, Eagle and Finney, Farming Press, United Kingdom 1993.
Basic design features of direct seeding drills
1. WIDE TINE SPACING (400mm minimum), 3-6 rows of tines, wide spacing between rows of tines
(400mm minimum)
2. HIGH TINE BREAKOUT (100-200kg), tines mounted on stiff frame
3. NARROW POINTS (20-40mm) for minimal soil surface disturbance
New drill or modify my old one?
A new trash seeder at $30 000 is an
investment that’s hard to justify, particularly as most cropping farmers in Tasmania require a versatile machine that can
cope with conventional sowing one day
and direct drilling the next. Existing
seeders can be modified for as little as
Modifying a seeder may require some
engineering skills and equipment which
not all farmers have. There is also the
525mm (21”) between times and 450mm (18”) between rows provides
need for knowledge on how to go about
adequate trash clearance through the chilvers’s converted shearer drill.
modification. Has somebody done
something simple, cheap and effective to
a seeder like yours? The following case studies are some good initial ideas and contacts. Also, contact
the DPIWE Topcrop program for a copy of There’s no money in dust, a Victorian drill conversion guide.
Drill conversions
Moreton Jenson, ‘Carinya’, Bishopsbourne
14 run Shearer disc drill box mounted on homemade frame with Pacific tines & boots, and
Superseeder points
➢ sows over 3 rows with clearances of 750mm(30") between rows and 550mm(22") between tines
➢ cost of materials including old drill was about $4500
➢ Moreton has mounted the box 600mm above the frame which in hindsight is excessive for 3 rows. It
could be dropped 100-150mm, and the capacity of the fertiliser box increased to about three times the
size of the seed box.
Moreton likes the way the tine design and narrow machine width allow even depth placement over undulating ground.
The drill is mainly used to sow autum oats into runout pasture which has been sprayed off sometime in
May. After grazing and harvesting, the stubble is burnt in Feb/March, s-tined and pasture seed spun on.
Early germination is assured under irrigation.
direct drilling allows longer cropping rotations,
with less time on the tractor
Essential features of direct
1. wide tine spacing
2. high tine breakout force
3. narrow points
Direct drilling is appropriate
for all soil types
Modified Inter 6-2 with Ryan trash float and press wheels.
Barley direct drilled into mulched pea stubble.
Heavy green pea stubble at Nile was flail mulched
after January harvest and followed with direct drilled
barley in May. No grazing or baling.
“The soil loves it.”
Modified Shearer 4-row trash-culti sowing barley into barley stubble
Stock and direct drilling don’t mix
⇒ 25-50 mm of friable surface tilth is a key
prerequisite for good seed/soil contact
⇒ KEEP STOCK OFF stubbles you intend
to direct drill into.
We converted our drill in 1993
By 1995 we were cropping 30%
more area. Annual tractor hours
have actually fallen over this
Michael Chilvers - Nile.
Peter Skirving (right) of Cressy, explains
some aspects of his home-made undercarriage
to a group of Topcrop farmers.
International 6-2, Ian MacKinnon, ‘Glen Esk’ & ‘Snaresbrook’
Lifted seedbox 150mm (6").
Tine frame - old one removed and Ryan frame fitted
with 24 Ryan tines with spear points. 230lb breakout,
$160 each.
Press wheels (Sharmans, SA) walking configuration.
Press wheel pressure: 1.8kg per cm of press wheel
width in cultivated ground and 2-3kg per cm width in
direct drilling ground. Press wheels cost $170 each.
Cost about $16,000 including the original drill but not
including 50-60 hours workshop labour.
Chamberlain 6 row trash seeder, Duncan Mills,
‘Leverington’, Cressy
Walking configuration press wheels
behind converted Inter 6-2.
originally 3 rows cultivation and 3 rows seeding,
modified to sow over all 6 rows,
removed cultivating tines and lifted seed box 900mm(3
feet) so that fertiliser and seeding tubes fall 45° or
on each tine, a long u-bolt holds the following
arrangement in place behind Primary Sales points
slotting to 100mm (4") deep:
- the fertiliser tube, fertiliser deep banded at the
bottom of the slot
- smudge bar (25mm wide) collapses the sides of the
slot and determines the depth of seed placement
- seed placement tube, seed falling on smudged trench
- 6 links of chain to drag soil over seed
tine breakout force increased with second springs and
heavier 3/4" rod,
a hot air system prevents condensation & blockage of
fertililiser tubes based on a Holden car heater.
Heavy stubbles & future modifications
➢ heavy stubbles and header rows are still too much for
the modified drill and disc colters to cut ahead of the
tines and work deeper with narrower tines could be
➢ a ‘straw storm’ straw spreading system for the header
would avoid bulky header rows
➢ tried Ryan narrow points but too much surface
disturbance, which reduces effectiveness of residual
weed control
Topcrop agronomist, Geoff Dean, inspects seed
placement behind converted Chamberlain
6 row trash seeder.
➢ approx $50 per tine assembly excluding chain and rear
bracket assembly
➢ one month in the farm workshop
➢ Primary Sales points $16 each
International 6-2, Peter Skirving, ‘Fairbanks’ , Cressy
International 6-2 20-run combine
built 3 row float frame of 3" box and 1/4" x 3" flat
designed and constructed own tine clamps and shear
➢ Janke tine and points
➢ tine spacings of 19"(475mm) between rows and
21"(525mm) along rows
For conventional sowing, the Skirvings simply remove the
direct drill float and replace the original float, the machine
thus retaining its versitility.
Steel for float frame, bolts, clamps etc
Janke tines @ $25 each
Janke points @ $10 each
tungsten tipped by local engineer @ $5 each
Shearer trash culti, PJ & NJ Chilvers
‘Winburn’, Nile,
The home-made undercarriage in place
showing home-made claps with shear-bolt
release and Janke tines.
Shearer Trash Culti drill, G series, 24- run, 4-row
Raised seed-fertiliser box 300mm (12")
Removed cultivating tines
Seeding tines spread evenly across all 4 rows to achieve spacings of 450mm (18") between rows and
525mm (21") between tines along each row, maintaining the standard planting intervals of 175mm
The machine remains versatile, alternating between 100mm points for conventional sowing and
knock-on lucerne points for direct drilling.
Tine breakout at about 160lbf is ok for sowing into reasonably friable soil. Sowing directly into sprayed
out pasture is not achievable on stock compacted
loams or black cracking clays.
For pasture establishment, poor depth control
remains a problem associated with minor humps
and hollows in the paddock. The machine is
unable to cope with these changes.
Press wheels recently purchased will improve
seed/soil contact, particularly for spring direct
drilled cereals.
Janke press wheels with 25mm hollow tyres
have recently been purchased for approximately
$200 each.
trash flow
Tine layout on converted 4 row Shearer
to maximise free flow of trash
How the implement breaks the soil
When the implement engages with the soil, the soil is either loosened or compacted Unfortunately it’s not
simply a case of deciding which we want, and selecting the appropriate implement. There are many soil
and implement factors influencing the final outcome, the most important being soil moisture.
If you were to extract a neat, undisturbed block of soil with
your spade, and gradually stand on it, the block of soil would
resist your weight up to a certain point, then suddenly break.
When a force is applied to the soil it can break in one of three
1. Brittle failure
Soil crumbles along a well defined natural planes of
weakness. The soil is loosened.
2. Compressive failure
Soil shears along an infinite number of planes. Occurs in wet
conditions or deep conditions where uplift is confined. The
soil is compacted.
3. Tensile failure
Soil is placed under tension. Soil breaks along well defined
natural planes of weakness. The soil is loosened.
Brittle or tensile failures are required for all types of
loosening and clod breaking operations. Apart from their
Loosened soil behind the paraplough working
cutting action, discs create a mixture of brittle and tensile
on a compacted headland. A mix of brittle
and tensile failure.
failures, as do forward inclined tines, and powered
implements used carefully.
➢ Compressive failure is bad. If the soil is moist, any implement will cause this kind of failure.
Occurs as a result of heavy loads applied to the soil or by tines working below critical depth (see tines
➢ Tensile failure is the most efficient way of loosening a soil in terms of power requirement, and
allows loosening at slightly higher soil moisture contents. The mouldboard plough or winged tines
produce tensile failure.
Tyre pressures and compaction
The degree of compaction is very sensitive to tyre pressure. Reducing tyre pressure is an avenue
relatively easy to follow compared with other ways of reducing compaction such as avoiding stocking
cropping paddocks, keeping trucks off the paddock at harvest, or tilling and harvesting only in dry
depth of compaction is determined by axle load
degree of compaction is determined by tyre pressure
truck tyres
tractor tyres
farm 4wd tyres
radial tyres
flotation tyres
If you have dual wheels on the tractor, the above rule
shows the importance of reducing tyre pressure in all
tyres, otherwise the degree of compaction remains the
same as without duals.
Most new tractors are now supplied with radial tyres
which operate at lower pressures than cross ply tyres.
Tined Implements
➢ deep rippers
➢ chisel plough
➢ cultivators
➢ S tine
Tines are immensely variable in their effect on the soil, depending on angle,
width, depth and springiness of the tine, and the condition of the soil. Nearly
all seedbed preparations involve a tined implement, whether as a primary
loosening tool or as secondary levelling and clod breaking tool.
Shallow tined cultivations - the S tine
For all soil types, the S tine is one of our most valuable and highly
recommended tillage implements, particularly when combined with a
front levelling board and rear crumble roller. It is gentle on soil structure,
produces a good seedbed tilth and has a low draft requirement. It is
recommended by poppy and onion company field staff as generally the
best implement to use for the final pass.
the S tine is one of our
most valuable and highly
recommended tillage
implements - every farm
should have one.
Tines for primary cultivation
The aim of chisel ploughing, ripping or subsoiling is to heave and shatter the soil, not to compact and
smear below the surface. It’s worth getting off the tractor and having a quick dig behind the implement to
make sure you’re not operating below critical depth.
loosening (brittle failure)
soil surface
............................. critical depth
smearing & compaction
(compressive failure)
A tine operating below critical depth, causing
long term damage to the soil.
Single ripping tine operating above critical depth
showing soil loosened above the 45° line.
Staying above critical depth
Some factors that reduce critical depth and reduce the effectiveness of subsoiling are illustrated below:
Tine inclination increasing
Above critical depth
Direction of travel
Tine width increasing
Soil movement
Brittle failure
Below critical depth
Soil moisture content increasing
Soil movement
Brittle failure
Soil surface condition
Also, avoid placing depth wheels near tines
as these restrict upward movement of the soil and make
compressive failure more likely.
Very compact
Adjust your tine spacing
Notice in the previous diagram how above critical depth, soil fails at about 45 degrees. Tine spacing must
be sufficiently close to avoid leaving undisturbed ridges of soil below the surface. Unless this is
investigated with a spade, the operator continues to do a poor job of the whole paddock.
Recommended tine spacing for various implement configurations and depth of work
conventional narrow tines
1 to 1.5 times depth*
winged tines
1.5 to 2 times depth
winged tines & shallow leading tines
2 to 2.5 times depth
*not including loose surface soil, eg ploughed before ripping
Is deep ripping worthwhile? (300mm plus)
A recent United Kingdom study of ripping between 300 and 375mm depth (12-15"), found a positive
response of crop yield in only 3 out of 76 paddocks. Unless a hard layer is very obvious from an
examination of the profile, there is unlikely to be any benefit.
According to the Kondinin Group*, in Australia deep ripping is mainly applied to sandy, light textured
soils where a traffic pan has developed. The lower the clay content of a soil, the deeper the hard layer.
Deep sands develop a layer at about 30cm depth, and loamy sands about 20cm depth. Duplex soils will
have traffic pans if the clay is deep enough, but generally do not respond to ripping unless the clay is
deeper than 25cm.
Shallow ripping (200-250mm or 8-10")
This is the most common ripping operation. It aims to shatter the topsoil to just below the plough depth.
➢ adjust tine spacing to avoid ridging - a 1:1 ratio of depth to spacing for narrow tines
➢ a good way of achieving sufficient depth of tilth for the potato
planter to operate, but make it one of the last passes in the
Avoid Recompaction
preparation sequence to avoid recompaction
➢ Soil after the ripping
➢ commonly used prior to a shallow powered implement pass,
operation is highly
recompaction being the only problem here
susceptible to recompaction
➢ ripping after harvest is ok provided soil moisture is not too
➢ Make your deepest working
high causing ‘knife through butter’ syndrome, but it’s best to
last in the preparation
sow oats, lupins or short term ryegrass to open up the soil for
the next crop
➢ ripping on the contour can be a valuable means of avoiding
erosion while the rest of the paddock is being harvested
How long do the beneficial effects of ripping last?
Unless actively growing roots grow into the new cracks created in the ripping operation, the effects are
quite temporary - just a few weeks or months. Rip during peak growth of a ryegrass green manure to
make the most of the ripping operation. The longer your can avoid recompaction the better.
Do not rip duplex soils
Duplex soils which containing a pale spewy layer between the topsoil and the clay are very unstable.
Ripping disrupts any natural pores in this layer and waterlogging is likely to be worse after deep ripping.
Subsoiling into the clay can cause a permanent degradation of the soil’s cropping capability. Chisel
ploughing of the topsoil is a good primary cultivation technique for these soils.
* The Seeding Edge, (2nd ed, 1993), Kondinin Group, Belmont, WA ph (09) 478 3343
* See also Deep Ripping on Cropping Soils and Crop Production, Ellington, A., in 4th Australian
Agronomy Conference Proceedings, 1987. Aust. Society of Agronomy. and
An Experimental Investigation into the Deep Loorening of Soils by Rigid Tines, Spoor, G. and Godwin,
R.J., National College of Agric. Engineering, Silsoe, Bedford, U.K. J. Agric. Engng. Res., (1978) 23,
It is generally thought that discs are not good for the soil. Why is this?
Probably because discs were once the farmers only tool beside the chisel
plough, and thus took the blame for much of the soil degradation that has
occurred in the past. Discs are not necessarily any worse than other
implements at our disposal today, but like any implement, can cause great
damage to the soil if used incorrectly or at the wrong soil moisture content.
➢ off-set discs
➢ one way plough
Discs and soil structure
The cutting action of discs take no account of the natural
fracture lines of the soil. Cutting forms new aggregates with
shinny smooth faces. The smearing becomes severe as soil
moisture increases, so that in wet conditions, discs are very
damaging to your soil. Discs can also overwork sand and
duplex soils if two or more passes are involved.
Discs for minimum tillage
Discs are best used together with tined implements in a
topworking tillage system, appropriate for all soil types,
particularly sands and duplex soils. Discs are an excellent
tool for chopping and shallow incorporation of coarse organic
matter, reducing trash load for subsequent sowing.
Shallow incorporation of surface stubbles or residues
promotes biological activity and breakdown, reduces trash
load for subsequent tined operations, and leaves sufficient
cover for wind and water erosion control. Its a good half way
between leaving it all on the surface and deep burial. Left on
the surface, organic matter has minimal contact with soil
organisms and is too dry most of the time for biological
activity. Deep burial disrupts soil structure and opens up the
soil, exposing humus to breakdown, so that in effect more
organic matter is lost than gained.
Discs are excellent for chopping and
incorporating stubbles. Use discs for
topworking sandy and duplex soils.
The mouldboard plough
Faced with the challenge of preparing a seedbed, farmers in Tasmania commonly opt to use the
mouldboard plough in their tillage sequence. Correctly used, the mouldboard plough is an excellent
implement for incorporating crop residues or green manure crops, and requires a minimal number of
passes of secondary tillage to produce the seedbed. However, for some Tasmanian soils, the mouldboard
plough is not appropriate. Soils prone to wind erosion are protected by coarse organic matter in the
surface layer which is buried in a mouldboard plough operation. Some soils are too shallow for
mouldboard ploughing and these are permanently degraded as low fertility, structurally poor subsoil is
mixed with the shallow topsoil.
Inversion is the action of the mouldboard plough. Have a look at the paddock to be worked and decide if
inversion is required, taking into consideration:
➢ the requirements of the seed to be planted, (small seeds require finer seedbeds)
➢ the moisture and structure of the soil, (very wet or dry, cloddy or fine)
➢ surface cover (amount and type - pasture, green manure, stubble)
Plough performance
Finishing the paddock in record time is often the main
yardstick of plough performance. In fact, the plough can
produce a wide range of soil conditions, from an almost
unbroken furrow to an open, broken finish with
considerable loosening, by adjusting depth and speed of
operation. Different mouldboard shapes are available to
achieve similar soil conditions at different depths and
Secondary problems arising after ploughing are largely
associated with incomplete burial, cloddiness, levelness or
openness of the surface and these can be minimised by
making adjustments of depth and speed, or by changing
mouldboard shape.
Where’s the skill in ploughing?
The mouldboard plough in action showing coulter
(bottom centre), skimmer (centre right). The
skimmer shaves the top corner of the slice before
inversion to achieve complete burial.
setting up the implement and tractor. Read the plough
manual - you’ll be suprised what you might learn.
producing the desired finish.
What finish does a good ploughman aim for?
Level surface. Each pass should turn onto the last pass
without noticeable difference and every board should
turn its furrow identically.
Tight finish. Lower speed means the board doesn’t throw the furrow leaving a loose, unconsolidated
finish. Soil structure is less disrupted, secondary pass wheelings are less severe, and a better seedbed
is achieved with a tight, firm finish.
For a well finished ploughed paddock, a single shallow (50mm / 2") powered implement or s-tine pass
before sowing is all that’s required. If a roller/packer is towed by the plough, the paddock and well
structured paddock be sown directly. A rough, loose finish requires extra work to level and firm.
How deep should I plough?
Never plough deeper than the topsoil. Incorporating subsoil is more expensive than you think. Subsoil is
very low in organic matter and therefore supplies few nutrients, degrades topsoil structure and is of little
use for crop growth. Soil tests show that each centimetre of krasnozem subsoil requires $700 worth of
fertilisers and 8500kg of organic matter per hectare before it approaches the value of topsoil. Twenty
green manure crops would be required to supply this amount of organic matter.
Popular makes of mouldboard ploughs are generally designed for deep, fertile European soils. This shape
of board does a poorer job of burial and evenness of finish when attempting to plough shallower than
150mm (6").
Sandy soils
Do not mouldboard plough sandy soils. Any soil low in organic matter is prone to erosion. Coarse
organic material is a sandy soil’s natural defence against erosion. Placing it at the bottom of the plough
layer is asking for trouble. This hazard is greatest for the sand and sandy loam soils of the state where in
dry windy conditions, wind erosion is noticed first on the mouldboard ploughed paddocks.
➢ Do not mouldboard plough sandy soils.
➢ When possible, these soils should be topworked with tined implements in a minimum tillage or direct
drill system.
Duplex soils (sandy loam over clay)
Mouldboard ploughing is appropriate for deeper duplex soils
only. The topsoil is the uppermost layer, usually darker and
higher in organic matter than the pale spewy layer below.
Never plough deeper than the topsoil. If the topsoil is less than
100mm (4 inches) deep then the soil is not suitable for
mouldboard ploughing. 100-150mm (4-6") is marginal.
Many shallow duplex soils are prone to both wind erosion (on
the banks) and waterlogging (in the hollows). Mouldboard
ploughing early and leaving the fallow ‘open’, may help keep
topsoil dry to allow early spring seedbed preparation, but this
is at the expense of long term sustainability. Organic matter
and structure decline under long fallows, increasing the risk of
erosion and degree of waterlogging. These soils are best
managed under a program as follows:
1. surface drainage linking hollows with broad shallow
2. subsurface drainage where appropriate (seek professional
3. minimum tillage and stubble retention/incorporation using
tines/discs and trash handling drill
Cropping beyond the lands capability.
Do not plough shallow duplex soils.
Krasnozem soils, Cressy soils and loams
Mouldboard ploughing is highly appropriate for these soils. Intensive cropping requires incorporation of
large amounts of organic matter, well prepared seedbeds and good weed control. The mouldboard plough
achieves these requirements while being relatively gentle on the soil’s structure.
Black cracking clays
Mouldboard ploughing is less appropriate for these soils.
➢ These soils are self mulching, creating a natural seedbed during shrink/swell cycles. This will only
occur if stock are kept off the paddock.
➢ By carefully using the self mulching capability, only minimal tillage is required. Shallow topwork
with tines or discs at the optimum moisture content.
If you do plough black cracking clays, a level finish is particularly important because the seed can be
sown in the natural, self mulched surface tilth produced overwinter. A rough ploughing operation requires
levelling prior to sowing. Levelling knocks the self mulched surface tilth into the hollows and exposes
unweathered clay on the humps. This is a difficult seedbed to sow into. Black cracking clay paddocks
are often ploughed rough with the aim of drying out the surface. If drainage is sorted out then a rough
finish is not required.
Rough Finish
A poor seedbed with pieces
of exposed, unweathered clay
Self mulch tilth
Before levelling
Smooth finish
An ideal seedbed
no exposed, unweathered clay
After levelling
Before levelling
Minimum tillage & the mouldboard
Loss of structure and fine organic matter
(humus) goes hand in hand with the amount
of soil disturbance. Powered implements
tend to maximise disturbance with their
stirring and mixing action, tines cause
minimal disturbance, while the mouldboard
plough lies somewhere in between.
The furrow press has been recommended for
Tasmanian soils by visiting international specialists
in soil management. The plough/press will produce
a seed bed in a single pass on duplex or well
structured clayey soils. Agfest 1995.
Powered Implements
During the cropping phase soil structure tends to decline. Good soil
management is all about slowing the rate of decline to a minimum.
Powered implements used without care and skill degrade soil structure
very rapidly by overworking or operating in soil too moist for tillage.
➢ roterra
➢ rotary spikes
➢ rotary hoe
Powered implements are immensely variable in their action on the soil. At best, they create a level, firm
seedbed, chop and incorporate coarse organic matter and break clods all in a single pass. What more
could one ask for? However, at worst, in a single pass powered implements can create more damage than
any other implement, while appearing to do a fine job.
Powered implements and soil structure
Overworking and working in moist soil conditions are the two chief problems associated with powered
implements. Soils with a history of powered implement use tend to;
➢ require more energy to form the seedbed each year
➢ suffer ‘clods and powder’ seedbed syndrome
➢ suffer poor drainage as natural pores and cracks are
Powered implements force the soil to
fracture along new lines, forming new
➢ crust more readily
➢ have a high wind and water erosion risk. An
Gentler implements allow the soil to
overworked surface layer can act like a sponge,
fracture along existing lines of weakpreventing excess water moving down through the
ness, forming natural aggregates.
Why use powered implements?
As a risk management tool. For intensive cropping where
planting and harvesting occurs like a dog chasing its tail,
there simply isn’t time for several tillage passes all at the
right moisture content or for long fallows where natural
weathering does the work. Gentler implements can be
used most of the time, while the powered implement is
there when the ‘instant seedbed’ is urgently required.
➢ To shallow chip and semi-incoporate surface cover or
dessicated pasture. Deep, slow powered implement passes
are worst. These maximise loss of organic matter and
destruction of natural structure. Do not use these
implements for deep working. Use tines such as the
agroplough for minimal surface disturbance or the chisel
plough for disturbance right to the surface.
Where is the skill?
Shallow chipping and incorporation is a good
way to use the powered implement. Use the
mouldboard plough for excessive surface trash.
In avoiding overworking. Judging just how much energy
to apply to the soil and adjusting rotary speed and forward
speed accordingly requires considerable expertise.
➢ In judging soil moisture. See earlier chapter which
illustrates the simple roll test for assessing soil moisture.
Sands and duplex soils
Overworking to a ‘clods and powder’
seedbed is a major problem for these soils.
Use of powered implements tends to make
this scenario more likely, bringing on
associated problems of rapid loss of organic
matter, wind erosion, waterlogging and
surface crusting. All these are exacerbated
by intensive tillage.
A powered implement can be used with
care, either as a final, shallow low energy
pass or as a one pass total seedbed
preparation, with the aim of avoiding
numerous passes with discs and tines, some
of which will be poorly timed in terms of
soil moisture. A powered implement can
also be used for chipping turf for
preparation of a potato seedbed.
Clays and loams
Powered implements can be used with care
in these soils, particularly as a shallow, low
energy pass before sowing, as a ‘power
harrow’. In an intensive cropping system
where incorporation of large amounts of
green manure and stubble is necessary, use
the mouldboard plough rather than a deep,
high energy powered implement pass.
Overworking with a powered implement is all too easy.
Black cracking clays
Use of powered implements gradually reduces this soil’s ability to form a natural self mulching seedbed.
In bad condition, black cracking clay clods tend to disintegrate the implement rather than vice versa.
Guidelines for using powered implements
1. Avoid overworking - adjust rotary speed and forward speed to produce no finer seedbed than the next
crop requires.
2. Check soil moisture before starting work - if you can roll a sausage it’s too wet.
3. Use as a shallow (2-4", 50-100mm) working implement to chop and incorporate organic matter and to
produce the seedbed finish.
4. Do NOT use as a deep working implement (over 100mm, 4"). Use tines for deep loosening and your
powered implement for the surface finish.
Choosing the Right Implement
damage #
cracking &
Deep ripper
Rigid tines designed to work at or
below plough depth (10-18"/ 250450mm). Alleviates compaction
caused by trafficking and stock in
wet conditions. Breaks plough pan
if one exists (see soil inspection).
Two passes required using standard
narrow tines, one pass using
winged tines.
High soil moisture, smearing &
compaction below
the surface check before
up to 17 per
tine at
(18”) depth
cracking &
Rigid tines designed to work at or
below plough depth. Tine leg is
slanted sideways at 45 degrees
rather than vertically. Draft is
significantly reduced by having the
tine follow the natural line of soil
High soil
smearing &
compaction below
the surface check before
14 per tine
at 450mm
(18”) depth
Stiffly-sprung tined plough, wide
points (100mm). Leaves coarse
organic matter on the surface.
Good topworking implement. Two
passes usually required.
High soil
smearing &
compaction below
the surface -check
before working.
clods &
Off set discs
Disc plough
One way
Semiburial of organic matter
leaving some on the surface for
erosion control. Good topworking
implement. Very detrimental to
soil structure if used in moist or
wet conditions
High soil
smearing- check
before working
7.5 for
Sows the seed by opening a furrow
using a disc or tine and boot.
High soil
smearing under
High soil
smearing - check
before working.
Wind erosion
kN/m of
Complete or partial burial of
organic matter, rough or smooth
finish, firm or loose finish,
depending on adjustment of colters,
skimmers, depth and speed.
Invert soil
Increase soil
Conserves moisture in the seedbed
and increases soil/seed contact for
even germination. Tow behind the
drill. Best at low speeds.
Increase soil
density &
break clods
Furrow press
Heavy cast iron rings with a sharp
cutting angle. Commonly towed
behind mouldboard plough in
Europe. Reduces number of
secondary tillage passes. Reduces
erosion risk.
High soil
moisture - check
before working
Finer surface
For disintegration of surface clods.
More effective at higher speeds
High soil
moisture - check
before working
Break clods,
level surface
Smudge with short vertical spikes
extending into the plough layer. No trash
handling ability. Good secondary
implement to follow mouldboard plough.
Preserves moisture. Levels surface.
High soil
moisture - check
before working.
Tractor powered. Vertical spikes or
blades rotating about a vertical axis.
Stirring and clod breaking action.
Fineness of tilth depends on forward
speed. Leaves more coarse organic
material on the surface than the rotary
hoe. Severely damaging to soil structure
if used incorrectly (tilth too fine or soil
too moist).
High soil
smearing &
below the surface
- check before
30 for
10 for
clods &
Rotary hoe
Tractor powered. Horizontally angled
blades rotating about a horizontal axis.
Mixing and clod breaking action.
Fineness of tilth depends on forward
speed. Leaves less coarse organic
material on the surface than the power
harrow. Severely damaging to soil
structure if used incorrectly (tilth too fine
or soil too moist). Can cause a hoe pan to
High soil
smearing &
below the surface
- check before
30 for
10 for
clods &
Tractor powered. Spikes rotating about a
horizontal axis. Mixing and clod
breaking action. Fineness of tilth
depends on forward speed. Chops and
incorporates clods and coarse organic
material. Severely damaging to soil
structure if used incorrectly (tilth too fine
or soil too moist).
High soil
smearing &
below the surface
- check before
30 for
10 for
Sort clods to
the surface
Break clods
S tine
Springy, forward inclined tines sort and
break clods with low input energy. 4 or 5
rows of tines give a levelling effect while
crumble roller firms the seedbed. Good
topworking implement. Excellent as final
pass before drilling.
High soil
moisture - check
before working.
burial or
allow direct
Flail mulcher
or slasher
Smashes standing cereal straw, green
manure or crop residue into smaller
pieces on the soil surface for
incorporation. For direct drilling into
cereal stubbles, mulching improves flow
of stubble past drilling tines.
residues &
kN/m of soil damage
* kN per metre of working width of implement, from Soil Management, 5th Ed, Davies, Eagle & Finney, Farming Press, U.K., 1993.
# Refers to the implements soil degrading capability if used incorrectly or inappropriately.
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