Chemistry Reference
In-Depth Information
and pull-out, are generally influenced by two main root properties: root tensile
strength and root architecture.
122
The effect of different root architectures
within woody root systems has been studied through the use of root analogues
to assess pull-out resistance. Tap roots (single roots which grow vertically
through the soil) have the least resistance to pull-out whilst dichotomous roots
(roots with branches off the main axis) are the most resistant.
122
Woody plant
species may be used to increase slope stability in areas prone to mass-wastage
events. Smaller scale erosion caused by overland flow of water is managed
more effectively by the use of vegetation with fibrous roots.
One of the limitations of woody root systems is that soil-surface coverage is
significantly less than that provided by species with a typically fibrous root
system, such as grasses. Fibrous root systems have a greater volume of roots in
surface soils,
123,124
increasing surface soil stabilisation better than woody roots.
Increasing soil coverage reduces splash erosion through interception of rainfall,
with plants having a finer root system typically contributing more to surface
coverage, and with the combination of canopy and roots reducing soil loss.
125
Vetiver grass has been researched widely for use in land-restoration projects.
Compared with a typical fibrous root system, Vetiver's root system is finer and
denser, with the ability to penetrate deeper into the soil. Roots have been
found to extend up to 3 metres deep in 12 months with an ability to adapt to
adverse soil conditions.
126
The application of such grasses in an agricultural
context is to create buffer strips which act to both stabilise soil but also catch
eroded material from cropping areas.
126
The use of vegetation to control erosion and landslides has the added benefit of
improving soil fertility. All plants can help restore soil organic matter, critical for
maintaining soil structure and soil hydraulic properties. Legumes can also increase
soil nitrogen. Soil organic carbon under grass and legumes can increase by ca.20%
in 4 years compared to a conventional till wheat system.
127
Restoration of
deforested areas in Brazil, using legume trees, showed higher stocks of C and N
over a thirteen year period when compared to a deforested area.
128
Soil erosion can be minimised through the use of vegetation stabilising soils
through surface coverage and also root inclusions. Fibrous root systems offer
the potential to stabilise the surface soils whilst tree roots penetrate soils deeper
and may reduce the risks of mass wastage events such as landslides.
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4.4
New Technologies
The recent global adoption of reduced tillage systems was described earlier in
this section. There are other technologies that are already in widespread use
that aim to decrease the physical damage of soil by farming. Low ground
pressure (LGP) tyres allow access to fields over a wider range of weather
conditions. Graham et al.
129
found that switching to LGP tyres increased
wheat yields by 6-7%. Vermeulen and Klooster
130
found a 4% increase in
potato yield with LGP tyres. Other studies have found minimal impact.
131
However, the cost of LGP tyres is high so it has been estimated that a farm of
