Transformation of the organic matter of steppe soils of the Trans-Ural region after their conversion into the reserved regime

Soils of the Arkaim Reserve were studied before the establishment of the reserve and, then, 12 and 18 years after the reservation of this territory. Former pastures and hayfields occupy 70% of the reserve, and former plowlands occupy about 30%. Some of them have been converted into sown meadows. The soil cover of the reserve is composed of chernozems (about 50% of the area), solonetzes and salt-affected soils (32%), meadow-chernozemic soils (7%), and forest soils (1%). In eighteen years of reservation, the C_org content in the upper 20 cm has increased by 0.5–0.8%, or by 14–25% of the initial content with the average rate of 60–100 g C/m² per year. The accumulation of C_org has been more intensive in the soils of former plowlands than in the soils of former pastures and in the chernozems than in the meadow-chernozemic soils. Self-restoration of most of the soils of the reserve is accompanied the rise in the content of the labile fraction of organic carbon. In some soils, the contents of the labile fraction (0.3%) and light-weight fraction (>25% of C_org) have reached optimum values. After 18 years of reservation, the biomass of microorganisms has reached 500–800 μg/g of soil (or 1.1–1.9% of C_org); the basal respiration has reached 0.7–1.5 μg C-CO₂/g per hour. These characteristics are the highest for meadow-chernozemic soils under former pasture and the lowest for postagrogenic chernozems. The rise in the C_org content and changes in the particular forms of soil organic matter under the regime of a reserve greatly depend on the soil type and on the former land use. The role of parent materials is smaller. Many soils of the reserve require a long period of rehabilitation.