Organic Carbon Pools and Microbial Communities Structure in Chernozem Under Conventional Tillage and No-Till

This study aims to evaluate the effects of soil management practices on SOC pools and microbial properties of Haplic Chernozem in the Rostov oblast. Soil under conventional tillage, no-till, and virgin steppe were studied. In the 0–5, 5–10, 10–20, and 30–40 cm layers, total organic carbon and the sizes of particulate and mineral-associated (C-MAOM) organic matter pools, isolated by particle-size fractionation, were determined. Microbial abundance, biomass, and taxonomic composition were assessed using quantitative real-time PCR and high-throughput sequencing. Compared with conventional tillage, no-till increased TOC content in the surface soil layer (0–5 cm) by 0.38%, along with a comparable decrease in deeper layers. Microbial biomass carbon, as well as bacterial and fungal gene copy numbers, declined under no-till in all studied layers. Ecosystem type and management had no significant effect on C-MAOM content or diversity indices prokaryotic and fungal communities. The taxonomic composition of the microbiome in virgin soil remained largely stable with the depth, whereas the agricultural use led to profile differentiation in prokaryotic and fungal community structure. The transition to no-till management in Haplic Chernozem did not result in net organic matter accumulation, but rather led to its vertical redistribution, with accumulation in the surface layer and depletion in deeper horizons.