The effect of grazing on biological activity and the ratio of fractions of mineralized organic matter of soils on carbonate rocks in the subalpine zone of the Eastern Caucasus

The article examines the effect of grazing intensity on the physico-chemical properties and biological activity of soils in mountain pastures of the Eastern Caucasus. The objects of the study were the soils of Leptic Umbrisols formed on the deluvium of Upper Cretaceous limestones at absolute altitudes of 1620–1660 m. Microbial biomass, enzymatic activity, and the size of the fractions of the pool of active soil organic matter were determined. It was found that intensive grazing in soils on the slopes of the southern exposure causes a decrease in the content of Corg and microbial biomass, while pH values, carbonate content, urease activity and soil skeletality increase. On the northern slopes, intensive grazing has a greater effect on a decrease in the activity of β-glucosidase and an increase in the activity of alkaline phosphatase, and also leads to an increase in the biomass of fungal mycelium. Intensive grazing has led to changes in the structure of the active pool of soil organic matter. The time of complete decomposition of hard-to-mineralize carbon fractions in the zone of intensive grazing on the slope of the northern exposure decreased by 2 times. On the slopes of the southern exposure, a decrease in the fractions of potentially mineralized and difficult-to-mineralize carbon was noted. At the same time, the content of easily mineralized carbon decreased to a lesser extent. In the soils of the northern slope, increased grazing intensity, on the contrary, causes a slight increase in the fractions of the active pool of organic matter. Thus, the organic matter and biological activity of the soils of the slopes of the southern exposure in the mountainous zone of the Eastern Caucasus are more susceptible to the destructive influence of grazing, which must be taken into account when calculating the norms of pasture load.