Grazing-induced alterations of soil hydraulic properties and functions in Inner Mongolia, PR China

Increasing grazing intensities of sheep and goats can lead to an increasing degradation of grasslands. We investigated four plots of different grazing intensities (heavily grazed, winter-grazed, ungrazed since 1999, and ungrazed since 1979) in Inner Mongolia, PR China, in order to study the effects of trampling-induced mechanical stresses on soil hydraulic properties. Soil water transport and effective evapotranspiration under heavily grazed and ungrazed since 1979 were modeled using the HYDRUS-1D model. Model calibration was conducted using data collected from field studies. The field data indicate that grazing decreases soil C content and hydrophobicity. Pore volume is reduced, and water-retention characteristics are modified, the saturated hydraulic conductivity decreases, and its anisotropy (vertical vs. horizontal conductivity) is influenced. Modeling results revealed higher evapotranspiration on the ungrazed site (ungrazed since 1979) compared to the grazed site (heavily grazed) due to wetter soil conditions, more dense vegetation, litter cover, and decreased runoff and drainage, respectively Grazing modified the partitioning of evapotranspiration with lower transpiration and higher evaporation at the grazed site owing to reduced root water uptake due to reduced evaporation and a patchy soil cover.