Chemistry Reference
In-Depth Information
reduced or zero tillage usually increases the amounts of pesticides applied to
control weeds. Under zero tillage, increases in weeds by 2-20 times can occur
in comparison with ploughed systems.
106
However, shallow, non-inversion
cultivation through reduced tillage could be used effectively to help control
weed populations whilst also not redistributing the weed seedbank.
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4.2 Biological Tillage
Soil compaction can be alleviated by the cultivation of plant species with a
strong and deep rooting root system that is able to penetrate mechanically
impeded layers. The roots also need to endure high levels of water saturation,
poor aeration and low redox potentials for some time. Two plants often used
for biological tillage are alfalfa and clover, which have the added benefit of
also fixing nitrogen that is vital to soil fertility. The root channels produced
under biological tillage produce continuous biopores that can be accessed by
subsequent crops. Along these biopores, exudation of organic compounds and
water uptake by roots induces aggregation and cracking of soil.
107
Plants with
deep and intensive rooting systems also incorporate organic matter into deeper
soil depths. Many feel that deep rooting plants offer considerable potential for
terrestrial carbon sequestration.
108
Soil pore structures formed by biological tillage often contain coarse and
medium-sized pores. These pores are rapid transmission pathways that
improve the flow of water and gases, and therefore promote (re-)colonisation
by micro organisms and fauna.
107
The conditions for subsequent crop growth
can be greatly improved. For coarse-textured soils, soils which are too wet, or
soils with other constraints for subsoiling, biological tillage provides a very
good alternative to deep loosening.
4.3 Vegetation and Root Reinforcement
Planting or managing vegetation is a very common practice to combat soil
erosion and stabilise unstable slopes against landslides.
109,110
Ugly grey
concrete or expensive reinforcing soil nails next to transport corridors are
being replaced by a range of plants whose roots reinforce the soil over a range
of depths.
111
In agriculture, planting of vegetation in severely degraded soils
increases mechanical stability as well as improving soil fertility.
112
The critical
factors in their contributions are rooting depth,
113,114
root distribution
115-117
and root diameter.
118
Much research has focused on the role of woody species in the stabilisation
of slopes and embankments due to their ability to penetrate deeper into the soil
than plants with a typically fine root system.
119
Tree roots provide both deep
anchorage and also reductions in pore water pressure through transpira-
tion.
120,121
As pore water pressures increase, soil instability increases until
failure occurs, where roots either break, due to excessive root tensile stresses,
or fail through pulling out of the soil. The two failure mechanisms, breakage
