Ambiguous effects of grazing intensity on surface soil moisture: A geostatistical case study from a steppe environment in Inner Mongolia, PR China

Does grazing intensity lead to changes in the mechanisms of water distribution and water storage in the topsoil? We attempt to answer this question by comparing temporal and spatial soil moisture variation on sites with different grazing intensities ranging from ungrazed to heavily grazed. The research was carried out in a semi-arid steppe environment in northern China. During the growing season, evapotranspiration rates usually exceed the amount of rainfall in these areas, so the ability to store water in the plant–soil system is crucial for biomass growth. In June 2005, the spatial variation of soil moisture in five grazing treatments (two ungrazed sites, one winter grazing, one continuous grazing and one heavy grazing site) was monitored on seven consecutive days after a precipitation event. We used capacitance sensors to measure volumetric soil moisture down to a depth of 0.06 m. The measurements were analysed with respect to the spatial correlation of data points (variogram analysis and kriging interpolation). The five sites did reveal some spatial patterns, but these were not very distinct. The capability of retaining water in the topsoil declined along the grazing gradient from ungrazed (wettest site) to heavily grazed (driest site). However, this pattern is disturbed, as the two ungrazed sites (ungrazed since 1979 and ungrazed since 1999) reacted differently to wetting and drying and showed significant differences on all sampling days.