Factors controlling the spatial patterns of soil moisture in a grazed semi-arid steppe investigated by multivariate geostatistics

Land use has a significant impact on spatial patterns of soil moisture, particularly in sensitive and poorly managed regions. This study evaluated the relative importance of soil, vegetation and topography in controlling the spatial moisture patterns in a grazed semi-arid steppe of Inner Mongolia. Five fields were investigated during 2004-2006: two ungrazed plots since 1979 (UG 79) and 1999 (UG 99); three grazed plots in winter grazed (WG), continuously grazed (CG) and heavily grazed (HG) with 0.5, 1.2 and 2.0 sheep units ha(-1) year(-1), respectively. The data were analysed using correlation and geostatistical analysis. Results showed that (1) grazing reduced the volumetric moisture contents (0-6 cm) and their spatial heterogeneity; (2) soil moisture patterns had weak to moderate spatial structures and (3) soil and plant properties, especially soil physical properties, were the main factors controlling spatial moisture patterns. Multivariate geostatistics further showed scale-dependent correlation for these controlling parameters depending on treatments. With increasing grazing intensity, heterogeneity of soil and plant properties decreased from a patchy to a homogeneous distribution. Specifically, the soil and plant properties strongly controlled the variation of soil moisture for UG 99 at short scale (45 m), and for CG and HG at long scale (90 m), however, weakly controlled the variation of soil moisture for UG 79 and WG. Our results have implications for the understanding ecohydrological processes of semi-arid steppe as well as model parameterization. We suggest that pasture management strongly modified soil moisture patterns, which should be considered in the hydrological models at multiple spatial scales. Copyright (C) 2010 John Wiley & Sons, Ltd.