Home' Grower : March 2010 Contents 22
The South Australian Grower -- March 2010
concludes his series on the importance of soil carbon with an
in-depth look at effective tillage methods
TILLAGE is one of the oldest and most effective
methods to prepare planting beds and to control
weeds. Unfortunately, it is also one of the most
abused methods -- resulting in soil loss, damage to the
soil structure and carbon loss through oxidation when
As a result of this opinions have shifted, with
many farming industries pushing no till using
herbicides and GMOs as sustainable agriculture.
The pendulum of opinion is beginning to swing
back to tillage now that the various problems of
chemical no till systems are emerging.
Tillage will always have a role in weed
management, soil aeration and building soil
health. Appropriate tillage does increase soil
carbon and ensures minimal erosion.
It is important that tillage does not destroy soil
structure by pulverising or smearing the soil peds.
Farmers should be aware of the concept of good
soil 'tilth'. This is soil that is friable with a crumbly
structure -- not a fine powder or large clumps.
Both of these are indicators of poor structure and
soil health. These conditions will increase the
oxidation of organic matter turning it into CO2.
Tillage should be done only when the soil has the
correct moisture. Too wet and it smears and
compresses. Too dry and it turns to dust and
powder. Both of these effects result in long-term
soil damage that will reduce yields, increase
susceptibility to pests and diseases, increase water
and wind erosion and increase production costs.
Correct speeds are important so that the soil
cracks and separates around the peds leaving
them in tact, rather than smashing or smearing
the peds by travelling too fast. Good ped structure
ensures that the soil is less prone to erosion.
Deep tillage using rippers or chisel ploughs that
result in minimal surface disturbance while
opening up the subsoils to allow better aeration
and water infiltration are the preferred options.
This will allow plant roots to grow deeper into the
soil, ensuring better nutrient and water uptake and
greater carbon deposition. Minimal surface
disturbance ensures that the soil is less prone to
erosion and oxidation, thereby reducing or
preventing carbon loss.
A large range of tillage methods can be used to
control weeds in crops without damaging the soil
and losing carbon. Various spring tynes, some
types of harrows, star weeders, knives and
brushes can be used to pull out young weeds with
only minimal soil disturbance.
Rotary hoes are very effective, however this
should be kept shallow at around 25 millimetres
to avoid destroying the soil structure. The fine inch
layer of soil on the top acts as a mulch to
suppress weed seeds when they germinate and
conserves the deeper soil moisture and carbon.
This ensures that carbon is not lost through
oxidation in the bulk of the topsoil.
There are several cultivators with guidance
systems that ensure precision accuracy for
controlling weeds. These can be set up with a
wide range of implements and can be purchased
in sizes suitable for small horticultural operations
to large broadacre farms.
However, as mentioned in a previous article in
this series, it is not always necessary to eradicate
weeds, and preserving vegetation cover is the
best way to prevent soil and carbon loss. Effective
management tools such as grazing or mowing can
achieve better long-term results.
Research shows that bare soils lose organic
matter through oxidation, the killing of
microorganisms and through wind and rain
erosion. Cultivated soils should be planted with a
cover crop as quickly as possible. The cover crop
will protect the soil from damage and add carbon
and other nutrients as it grows. The correct choice
of species can increase soil nitrogen, conserve soil
moisture through mulching and suppress weeds
by out-competing them.
There are various forms of organic no till
systems that sow directly into rolled, grazed or cut
cover crops and pastures with very effective
yields. As the soil carbon builds up, the yields
increase with many outperforming the
conventional crops in the district.
Details: OFA 07 4098, ofa.org.au
Tillage keeps weeds at bay
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nothing is at all "like it".
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