Influence of grazing on hydraulic and mechanical properties of semiarid steppe soils under different vegetation type in Inner Mongolia, China

Over the last few decades, due to increase in grazing intensity, animal trampling has led to soil structure deterioration in Inner Mongolia, China. We investigated two different steppe ecosystems: Leymus chinensis (LCh, characterized by relatively higher precipitation) and Stipa grandis (SG) and two grazing intensities: ungrazed since 1979 (UG79) and grazed (continuously grazed, CG, at the Stipa grandis site and winter grazed, WG, at Leymus chinensis). Soil mechanical and hydraulic properties of semiarid steppe soils from each site and treatment were determined for soil aggregates and disturbed and bulk soil samples from different depths (4-8, 18-22, 30-34 and 56-60 cm for disturbed and bulk samples and 0-15 cm for the aggregates). Grazing causes a significant increase in tensile strength of aggregates and in the precompression stress of the bulk soil as well as a decrease in air and saturated hydraulic conductivity, irrespective of the vegetation type. Furthermore, exclusion from grazing led to more pronounced recovery of soil strength and pore continuity and hydraulic conductivity at the LCh site but it also depended on the moisture conditions of the sites. Under wetter conditions as well as after repeated freezing and thawing the soil strength declined.