Observations on changes in soil properties in grazed and nongrazed areas of Alxa desert steppe, inner Mongolia

Soil chemical properties in different locations around and away front the perennial shrub Zygophyllum xanthoxylum in a west Inner-Mongolian desert of China were investigated in a freely grazed area (FG) and areas excluded from grazing for two (2EX) and six hears (6EX). The results showed that concentrations of soil organic carbon (SOC) and total N (N-t) were highest at the clump center, followed by the canopy periphery, and lowest ill the intershrub space in both grazed and non-grazed areas. Accumulation of SOC and N, in the clump center were significantly greater ill nongrazed compared to grazed areas. The nutrient enrichment ratios under the shrub canopy in 2EX and 6EX were greater than that in the grazed area, especially ill the 0-10 cm soil. Soils under the shrub canopy had a lower pH as compared to soils in the intershrub space, especially ill the 0-10 cm soil. Shrub cover, biomass, and the mound height around shrub crowns were higher in the nongrazed than the grazed area. Significant correlation between soil chemical concentration and shrub biomass suggests that fertile islands rely on the stability of the shrub communities. Grazing exclusion favors further development of fertile islands around the shrub, but did not improve the soil nutrient status in the intershrub space. Although shrub invasion into the grassland is generally considered as a desertification process, preservation of shrubs from overgrazing is of vital importance-in preventing the rangeland from further desertification.