Transfer and Accumulation of Biophilic Elements in Pasture Ecosystems of the Northern Caspian

The scale and consequences of the transfer of biophilic elements from pasture ecosystems to sheep farms in the clayey semidesert of the Northern Caspian Sea region under the method of pastoralism accepted in the region (on the example of Stepnovsky settlement of Pallasovsky district of Volgograd region) were estimated. For the calculations, we used data on the chemical composition of dominant plants and sheep faeces, the long-term average productivity of phytocenoses, information on the rate of consumption of pasture forage by animals, etc. Soils of pastures and the reserve area, and soils on the sheep farm (in sheep corrals and in their resting places) were investigated. At least 17 t C, 600 kg Ca, 260 kg N, 100 kg Mg, 50 kg K, 40 kg P and 1 kg S were transferred to farms (0.1% of the area) from 1 ha of pasture (15% of the area) during the 6 months grazing season. The long-term stocks of faeces on farms (more than 1 thousand t in the example under consideration) are practically excluded from the circulation in the landscape. Small areas of farm soils are enriched with C, N, P and K. Compared with soils of the protected area, stocks of water soluble K increase (in the 0–30 cm layer) by two orders of magnitude, exchangeable K increases by 12–16 times, C by 8 times, N by 3 times, mobile P by 2 times. In grassland meadow-chestnut soils a decrease in the content of C (1.3 times) and exchangeable forms of K (1.6 times) relative to soils of the reserve area, in solonets on pastures decrease in the concentration of elements is not noted. The absence of statistically significant differences in the stocks of biophilic elements between the pasture soils and the soils of the protected area is partially explained by an increase in soil density by 0.08 g/cm³ in the 0–50 cm layer of the pasture soils. With the existing farming method, it is necessary to control the balance of biophilic elements in pasture soils.