Introduction:
Because the origin vegetation is
changed into sparse vegetation or farmland, soil and water loss in Loess
Plateau of China is serious and became one of the most serious regions in the
world after human activity lasted for thousands of years. In order to conserve
water and soil and improve ecological environment, since 1950, a largescale
afforestation has been carried out on the Loess Plateau, and great progress has
been made.
Rainfall is the main way to
recharge soil moisture in perennial forest and grass in the most of the Loess
Plateau because groundwater table is deep and water resources are scarcity and
irrigation is limited.
Soil drought is easy to appear in perennial forest and
grass. Dried soil layer is the soil layer in which the soil water content is
equal to or lowers
than the distinguishing standard, wilt point With vegetation restoration,
soil and water loss reduced but the dried soil layer (DSL) appeared and then
the location DSL appeared becomes deep. The soil water environment in root zone
soil is getting worse because plant consumes large amounts of water which
destroy the relationship between soil water and plant growth and at the same
time, the recharged soil water is limited in perennial forest and grass.
Long term cumulative desiccation
of soil forms severe desiccation of soil and DSL occurs in deeper soil layer.
The soil desiccation causes soil water mobility reduces and the soil water
exchange depth weakens, which cut off soil moisture contact between the soil
layers higher than the MID and that in the soil layer lower than the MID. The soil
desiccation deteriorates soil water environment, slow down plant growth and
speed up plant communities’ recession. The declined forest and grassland is
difficult to be renewed.
Severe desiccation of soil
causes soil degradation and vegetation decline, which influences the
stability of forest vegetation ecosystem and national ecologic security system.
Controlling soil drought is important for vegetation restoration and
reconstruction of ecological environment.
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