Grazing Effects on Compressibility of Kastanozems in Inner Mongolian Steppe Ecosystem

In Inner Mongolia, animal trampling is one of the main factors causing soil degradation manifested by altered mechanical strength or changes in water and gas fluxes. Soil samples were collected at two depths (4-8 and 18-22 cm) on the Stipa grandis steppe ecosystem in Inner Mongolia from two treatments characterized by different grazing intensities: ungrazed since 1979 (UG) and continuously grazed (CG). The following mechanical soil properties were determined under static and repeated loading conditions: precompression stress, P-c; coefficient of cyclic compressibility, c(n), and compression index, C-c. Air conductivity measurements were used to quantify the changes in soil functions due to application of repeated loading. The CG site showed significantly higher precompression stress values (111 kPa) than the UG site (64 kPa) at the first soil depth. The highest c(n) values were found in the topsoil of the UG site, while the CG site had significantly lower c(n) values. Repeated loading caused higher soil deformation compared to the static loading test. It was also found that the strain of soil samples from the UG site was higher than the CG site. We found a good fit between c(n) and precompression stress. The C-c values of the cyclically loaded samples were significantly lower at the CG site than the statically loaded ones. The air conductivity of the UG site remained constant for a wider stress range of repeatedly applied stress compared with the CG site, which reflects higher stability of the soil pore network at the UG site.