Chemistry Reference
In-Depth Information
levels are enhanced. With greater carbon, soils are more resilient to
compaction, so they bounce back more after wheelings or livestock
trampling.
139
Considerable research has been conducted on soil carbon as it
underlies so many processes,
140-142
so this chapter has only provided a very
brief overview in the context of soil physical conditions.
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5 Case Study 1 - Soil Restoration in the Loess Plateau,
China
The Loess Plateau in China is unique and covers 624 000 km
2
comprised of
very fine soils, making it highly susceptible to wind and water erosion. For
over 5000 years the landscape has been influenced by human activity, resulting
in widespread degradation.
143
Erosion has been catastrophic due to large-scale
overgrazing and overuse of the land, resulting in widespread poverty and
abandonment of large areas no longer capable of agricultural productivity.
The Loess Plateau contains three main landscapes: tableland and gullies, hilly
land and gullies, and sand land. Soil erosion rates are high, with an average
5000-10 000 Mg km
2
per year, with some highly erodible areas producing
more than 20 000 Mg km
2
per year.
144
Natural vegetative restoration has been successful in reducing erosion in all
landscape and is widely accepted as the best strategy for minimising soil loss;
145
the type of vegetation, however, is important. In an attempt to increase
vegetation cover in erosion-prone areas, the Chinese government launched the
'Grain for Green Project' in 1999. The aim was to increase forest and grassland
coverage through the reduction of cropping on steep slopes most prone to
erosion. In Shaanxi Province the total vegetation coverage increased by 12.5%
in the 7 years since 1998. A large proportion of vegetation increase was
attributable to control of grazing by livestock; however, due to the manage-
ment of afforested sites to increase production, a net decline of 6.1% was found
in this type of land use.
146
As previously mentioned in this chapter, trees act to
increase soil stability through deep roots and also increase evapotranspiration,
reducing pore water pressures in the soil. Within some areas this has caused
conflict with increasing water scarcity due to water usage caused by
afforestation, necessitating the correct choices for sustainable water manage-
ment. Trees and shrubs create greater soil moisture depletion in soil depths of
1.0-3.0 m than natural grasslands and may, therefore, not be suitable unless
the soils are frequently wet.
147
Other types of vegetation in differing land uses
have the ability to increase soil moisture; these include cropland, fallow land,
and intercropping land.
148
Pine plantations are widely acknowledged for soil
erosion minimisation but may also increase runoff and compound compaction
and desiccation of soils, causing soil degradation in semi-arid areas.
149
Due to
the complexities of the interactions of plants and soils with the topographical
features of the region, structured approaches must be formulated to ensure
that benefits to one do not cost further degradation to others.
