Chemistry Reference
In-Depth Information
at least 200 ha is needed to recoup the costs.
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Another traction technology in
widespread use is tracks. These confine compaction to topsoil and distribute
the load more efficiently.
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LGP tyres and tracks decrease the contact pressure on soils, which decreases
topsoil damage, but subsoil damage depends on the overall weight of the
machine.
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One option is to use smaller tractors, but by nature they require more
passes to perform the same task as a larger tractor. With multiple passes, soil
damage increases, so lighter tractors can cause as much damage as larger
tractors.
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A technology attracting considerable attention is Controlled Traffic Farming
(CTF). Axle widths of different machinery are matched, with vehicles restricted
to dedicated tramlines. The approach was reviewed in detail by Chamen.
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CTF
and standard farming practices are now aided by Global Navigation Satellite
Systems (GNSS) that have a spatial accuracy of several centimetres and follow
specific tracks within fields. This technology lets farmers map problem areas,
apply precision inputs and develop highly efficient cultivation, spraying and
harvesting practices, where overlaps between passes are minimised. In a given
year, 95% of an agricultural field can experience at least one wheel pass.
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Using
a one-pass cultivation system, such as minimum tillage with auto-steer GNSS,
the amount can reduce to 45% and to less than 20% if direct drilling is used.
There is also potential to target improvements to crop roots so that they
respond better to physically limited soil conditions. In mechanically impeded
soils, for instance, roots preferentially grow through biopores.
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Screening
approaches can select cultivars with root systems that are better able to access
biopores.
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There is a considerable impact of soil physical condition on
resource capture between different varieties of the same crop.
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A major factor
driving differences between crop varieties will be the structure of the root
system, which has been recognised in the recent shift in plant sciences to
consider processes beneath the ground.
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4.5 Carbon
Powlson states ''From almost any viewpoint, it is desirable to maintain SOC
[soil organic carbon] content at as high a value as possible for the soil type and
environment as this is beneficial for a wide range of soil physical properties and
root growth''.
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Various practices exist to return carbon to soils, including the
better management of crop stubble, use of cover crops, amendments with
animal wastes produced on farm, or imports of carbon from off the farm. New
technologies produce forms of carbon, such as biochar, that are retained in
soils for long periods of time and are thought to help retain nutrients and
pesticides, and build soil structure.
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Carbon has various potentially positive impacts on the physical condition of
soil for crop production. It is a building block in the formation of stable,
aggregated soil
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that resists erosion and slumping, capping, or hardsetting.
Soil compaction damage has also been found to decrease when organic carbon
