Cropping
Wind erosion
Prevent valuable soil from blowing away
Failure to take steps to maintain soil cover can accelerate topsoil losses caused by wind erosion, particularly during late
spring and summer when soil cover is at a minimum. This article outlines farming and grazing management methods
that can minimise wind erosion and its impact on farm production.
by
John Leys,
CENTRE FOR NATURAL RESOURCES,
DEPARTMENT OF INFRASTRUCTURE,
PLANNING AND NATURAL RESOURCES
T
here is no single recipe for controlling
wind erosion but steps can be taken to
protect soil resources.
There are three basic control methods —
maintaining
ground
cover,
surface
roughening and chemical bonding.
Ground cover (pasture, stubble and weeds)
needs to be more than 50 per cent (as
measured when cover is flattened). Shrubs
and grass tussocks more than 100 millimetres
high need to be spaced no more than three
times their height when they are distributed
evenly across the paddock.
Surface roughening (soil clods and tillage
ridges) need to have 50% of the surface
covered with soil clods more than 20mm in
diameter and tillage ridges about 100mm
high. Surface roughening with clods is best
suited to loam and clay textured soils and not
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Farming practices that maximise residue conservation such as retaining stubble and maintaining a
surface-roughened paddock can help reduce wind erosion.
sands, which are best suited to ridging.
Chemical bonding requires the entire eroding
area to be treated with enough bonding
material to stop any erosion.
How wind erosion works
Wind erosion results in soil and nutrient
loss, scalding, reduced water infiltration and
the burying of on- and off-farm infrastructure.
It can also affect health, reduce visibility and
disrupt electricity supplies.
Wind erosion occurs when the force of the
wind exceeds the resistance of the soil surface.
On-farm, the most damaging wind erosion
process is saltation, which occurs when soil
particles, sized 0.1–0.5mm, are bounced
across the surface by the wind.
As the saltating particles crash into the
surface, they splash up more particles that
also bounce across the surface.
This bombardment of the surface causes
an avalanche that spreads out in a fan shape,
with more and more soil particles being
moved downwind.
Off-farm, the most damaging wind erosion
process is dust, which occurs when particles
less than 0.1mm are carried off-farm by the
wind. Larger dust particles (0.1–0.05mm) are
often dropped within a few kilometres of the
erosion site. Smaller particles (less than
0.005mm) travel thousands of kilometres and
are only washed out of the air by rainfall.
The erosion rate of a paddock will change
downwind and will be different at the start
and end of the erosion event. The amount of
soil being moved by wind erosion increases
downwind until it reaches a maximum.
For sandy soils, erosion can start 200mm
downwind and reach the maximum erosion
rate in about five metres from where the
erosion starts (such as the edge of a paddock).
The erosion rate of a paddock will increase
to a peak as the surface is bombarded by
eroding particles, then slow to equilibrium.
This occurs because as the erosion continues,
the surface starts to ‘armour up’. This
amouring layer comprises mainly of soil
Strip ripping at 750-millimetre spacing can
catch bouncing soil particles to reduce erosion.
The foreground of the photograph was ripped at six
kilometres per hour, while the background was
ripped at 13km/h which gave more clod. Inset:
50mm ripper points were used for strip ripping.
FA R M I N G A H E A D
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September 2003
Wind erosion
Cropping
particles that are too large for the wind to blow
away and of the remaining ground cover.
Armouring layers are a sign that significant
soil has already been lost because it is formed
when the finer particles in the top few
millimetres have blown away.
If the armouring layer is disturbed then
there is the potential for increased soil loss of
newly exposed soil.
Prevention is better than cure
In most sandy soils, it is difficult to control
wind erosion after it has started.
Prevention is the best control method,
especially in sandy soils where mechanical
and binding methods are either less effective
or too expensive (more than $500 per hectare).
Sandy soils tend to have little soil
structure and as such are better protected by
ground cover.
On cropping paddocks, adopt farming
practices that maximise ground cover and
reduce soil pulverisation. On grazing land or
fallow paddocks, destock early and keep
ground cover at more than 50%.
Rabbits are particularly destructive of
vegetation and loosen the surface when
digging for food. If erosion is already a
problem, do not use warren ripping because
it loosens soil. Baiting and fumigation
are preferred options for rabbit control in
these conditions.
In sandy or sodic soils, it is an advantage to throw up a ridge (requiring a wide point or delver) as well as
a clod. Pictured left is a 50-millimetre ripper point with delver for throwing a ridge in loose soil and pictured
right is a 50mm point with a Turlec wing.
Goats and kangaroos also can reduce
ground cover and need to be managed
to ensure cover does not drop below the
critical level.
Preserving ground cover
Maintaining more than 50% ground cover
is the preferred method of erosion control.
If erosion does start on a paddock, then try to
maintain any remaining ground cover.
Ground cover helps to control erosion by:
• Acting as a blanket that prevents the
wind from picking up any soil particles.
• Absorbing the force of the wind and
reducing the wind speed at ground level.
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Cropping
Wind erosion
many clods. Incorporate ridging into control
measures. Tillage ridges need to be about
100mm high and cover the entire erosionprone area. Ridges less than 100mm quickly
fill with sand and if more than 100mm the
ridge crest tends to erode quickly.
Loam and clay soils provide better results
with surface roughening. Treat the entire
eroding area plus some additional buffer
areas. Start roughening on the upwind edge
and work downwind if the landscape is flat.
On slopes, roughen on the contour.
Methods of surface roughening include
strip ripping and cultivation.
Cultivation with insufficient clod and low ridges created with 250-millimetre points on 230mm spacing (left),
while 50mm points on a chisel plough with 305mm spacing created good clod cover (right).
• Trapping eroded soil particles and
reducing the amount of bombardment in
the soil surface.
Aim to keep ground cover (stubble, weeds,
pasture and crop) at more than 50% when
viewed straight down.
Stubble, plants, grass butts or small bushes
(higher than 100mm) that sit up into the
air offer even more protection and mean
slightly less cover will be required.
Protection from bushes and tussock-type
grasses occurs when the spacing between the
plants is no more than three times their
height, distributed evenly across the paddock.
Surface roughening
Surface roughening helps to control
erosion by covering more than 50% of the
soil surface with clods that are too large
(more than 20mm) to be lifted by the wind.
Extra roughness can be made with tillage
ridges and furrows that can trap any loose soil
that may be moving. Consider using this
method only when there is insufficient
vegetation to protect the soil surface (less than
50%) or the soil type produces sufficient clods
to protect the surface.
Sandy soils are not suited to surface
roughening alone as they do not produce
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Strip ripping
Strip ripping can be used to catch the
bouncing particles before the soil erosion
rate reaches its maximum. This has the
advantage that the entire paddock does not
need to be cultivated.
A ripper penetrates the surface to a depth of
100–200mm and creates a furrow lined with
cloddy material. The aim is to create clod that
covers the loose material and catches any
moving particles.
Spacing of the rip lines is critical. Since
erosion can reach its maximum rate in less
than 5m, space out rip lines to no more than
2m apart (for example, 750mm). If erosion
has started or the area receives erosive winds
from different directions, rip lines need to be
close together and work best when the entire
surface is covered in clod.
Extra rip lines can be placed between the
first lines or ripped at right-angles if they fill
with sand and a second treatment is necessary.
In sodic soils, rainfall will disperse
clods, reducing roughness and requiring
follow-up ripping.
In sandy or sodic soils, it is an advantage to
throw up a ridge as well as a clod as this will
last longer than just a rip line. To throw up a
ridge a wide point or delver is required.
Factors to be aware of when strip ripping:
• On sloping ground, rip lines may
concentrate water and result in gullies.
• When insufficient clod is produced
during ripping, rip lines simply provide
more fresh soil to be eroded.
• On soils with salty, sodic or acid subsoils,
rip lines may turn over soil that will
reduce crop and pasture growth in the
future, so be careful not to bring subsoils
to the surface.
• When rip lines fill with sand, they form a
ridge that is difficult to level out after the
erosion season finishes. The aim is to
have enough rip lines to limit sand drift
and the ridges catch all the loose sand.
• In rangelands, rip lines may remove
valuable grass butts and fodder bushes,
making an ideal environment for woody
weed infestations. Plan carefully to
minimise damage to existing vegetation.
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Wind erosion
soil surface to form a crust that inhibits
soil movement.
The method is expensive and is best only
considered if capital improvements or highvalue crops are threatened.
• In New South Wales, if the ground cover
consists of more than 50% naturally
occurring native vegetation, consent
for clearing by ripping may be
required under the Native Vegetation
Conservation Act (1997). If unsure,
contact the local office of the Department
of Infrastructure, Planning and Natural
Resources before starting ripping or
cultivation. In other States, check with
relevant State or local authorities as to
whether any consents are required.
Cultivating land
For rough or ridged surfaces to be effective
traps, they need to be made of clods that are
too big to be eroded by the wind and ridged
enough to catch moving sand.
The aim is to keep the soil rough and
ridged to either prevent any movement in the
first place or to trap bouncing soil particles
quickly in the surface depressions.
Soil clods more than 20mm should
comprise more than 50% of the soil surface,
otherwise erosion will start again.
Cultivate a trial area to determine the
correct surface conditions are being created
before attempting to cultivate the entire
eroding area.
Tined implements such as chisel ploughs
and scarifiers with narrow (50mm) points
penetrate soil well and provide good clod.
Cropping
A surface with good ridge and clod formation was
created using 50-millimetre narrow points at
900mm spacing on the first row and 150mm points
on the last two rows at 450mm spacing.
If implements cannot penetrate dry soil,
wait for moist soil conditions.
To modify implements remove every
second or third tine to decrease draft.
Using narrow points (50mm) at 900mm
spacing on the first row and 150mm points
on the last two rows at 450mm spacing has
produced good clods and ridges.
Chemical bonding
Chemical bonding agents can ‘cement’ the
surface temporarily. These are sprayed on the
Managing land after rainfall
After rainfall, soil crusts form that reduce
erosion. If the crust or paddock roughness
and ridging is still adequate, no action
is required.
But if the crust has sand grains on the
surface or the clods and roughness have
been flattened, it may be necessary to
‘re-roughen’ the surface as the crust will
break down through erosion from the loose
sand grains.
The most common mistake with all
remedial measures is restocking the treated
area too soon.
Prevent livestock from entering a treated or
eroding paddock until there is enough
vegetative cover to control erosion (more than
50% cover). Keeping livestock out also
increases the ability of the soil crust and clods
to control erosion.
About the author
John Leys is with the Department of Infrastructure,
Planning and Natural Resources, Gunnedah, NSW
Email: [email protected]
Phone:(02) 6742 9509, Fax: (02) 6742 3129.
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