SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...

depletion, but also decrease the water availability and further increase soil
erosion by wind. Thus, it is essential to quantify and predict management effects
on soil properties to assess their consequences on plant production and the
environment. Many studies have focused on the effects of land management on
soil properties (Green et al., 2003). However, few studies have dealt with the
consequences of these practices on water and heat fluxes (Chung and Horton,
1987; Peth and Horn 2006; Ndiaye et al., 2007). Especially, considering the
stress-dependent changes of the environment, an adequate account of water
flow processes and its spatial variability based on hydrological models is still
lacking due to the complexity of the soil system (Ndiaye et al., 2007), although
there are widely applicable hydrological models like SHAW (Flerchinger and
Saxton, 1989), HYDRUS (Šimůnek et al., 1998) and SWAT (Neitsch et al.,
2002).
Especially, considering the amount of plant available water as one of the most
limiting factors for sustainable grassland development, the effects of grazing on
water-related mechanisms and water budgets is urgently needed to be
understood in our studied area (Chen and Wang, 2000). Some studies have
shown that grazing increases evaporation but decreases transpiration because
of increasing bare ground area and reducing amount of biomass. Therefore, the
heavily grazed sites are more susceptible to drought, and prone to being
degraded due to the reduction of available soil water (Snyman, 2005; Zhang et
al., 2005). However, to which extent grazing affects evapotranspiration, and how
far it is partitioned into transpiration and evaporation remains unclear (Leenhardt
et al., 1995). Furthermore, although water interception by the canopy and plant
residues might occupy large volumes of water in steppe ecosystems, it normally
is neglected or mixed with soil evaporation.
Moreover, it is widely recognized that the movement of water and heat are
closely coupled and strongly affected by each other, but their mutual interactions
are rarely considered in practical applications. Frozen soil normally reduces
infiltration capacity dramatically due to blocking of pores by the formation of ice
lenses. As a result, lateral flow and snow melt may release huge quantities of
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