Influence of grazing on the structure and biological activity of dry steppe soils of the southern Russian Plain

Abstract

A comparative analysis of physicochemical and biological properties of Kastanozems and Solonetzes, the two most common soil types in the Caspian region of the post-Soviet territory was carried out. The carbonate, salt, Corg, mineral N (NH 4 + and NO 3 À ) contents, microbial biomass (measured by ds-DNA and phospholipids), and activity of 17 hydrolases involved in the C, N, P, and S cycles were measured along the grazing attenuation gradient near a typical sheep farm with year-round grazing. Heavy grazing increases the number of Solonetz areas, they occupy up to 70% of the soil cover. Further away from the farm the areas decrease, and Kastanozems dominate there instead.Both in Kastanozems and Solonetzes, heavy grazing leads to soil salinisation, accumulation of carbonates and nitrates, decrease in ammonia and Corg content, microbial biomass, and enzymatic activity. At moderate grazing, a significant increase in microbial biomass and enzymatic activity throughout the soil profile, particularly in the 0-10 cm layer was found; at light grazing, it was observed mainly in deeper soil layers, not in the upper 0-10 cm. The microbial biomass and enzymatic activity of soils did not directly follow grazing load and was maximal at moderate grazing, where negative effect of reducing phytomass is compensated by large inputs of animal excreta, stimulating development of soil microbial community. Compared to Kastanozems, Solonetzes were more resistant to pasture load, and under heavy grazing, their properties changed to a lesser extent.