Particularities of Hydrolytic Enzymes Pool in Soils of Agricultural Terraces in the Eastern Caucasus

A study of the influence of farming practices in the Middle Ages (X–XV AD) on the activities of 11 hydrolytic enzymes involved in the biogeochemical cycles of basic elements in soils was carried out. Agrostratozems of medieval agricultural terraces of mid-mountain Dagestan (Plaggic and Hortic Anthrosol) were chosen as objects of study. In all cases, the enzymatic activity of the studied soils, in all soil layers, decreased in the following order: alkaline phosphatase phosphodiesterase acid phosphatase pyrophosphatase ≥ leucine aminopeptidase arylsulfatase chitinase β-glucosidase xylanase α-glucosidase cellobiohydrolase. The enzymatic activity of the studied soils was primarily determined by the amount of microbial biomass (Cmic). Thus, the activity of enzymes of various groups depended on Cmic by 61–94%. Agricultural practices associated with ploughing, manuring, and irrigation lead to convergence in the activity of nitrogen cycle enzymes in soils of the mountain zone, which is associated with similar features of the nitrogen cycle in agrogenic soils, regardless of bioclimatic conditions. The addition of organic materials has led to an increase in the physiological efficiency of microbial communities and the rate of enzyme production, and high levels of biological activity can persist in soil for about 1000 years. Ploughing with the application of organic fertilizers in the past led to an increase in enzymatic activity expressed per unit of microbial biomass (specific activity), and therefore this indicator can be used as an indicator of agrogenic transformation of soils in the past.