Long-term winter wheat cropping influenced soil organic carbon pools in different aggregate fractions of Chernozem soil

In this study, the role of the different management strategies was investigated, to elucidate soil organic carbon (SOC) loss under the long-term winter wheat cropping. Soil samples from wheat-based cropping systems and native vegetation were analyzed to assess SOC, total nitrogen, water-stable aggregates, mean weight diameter, and the carbon management index. Tillage practices involved moldboard plowing and field cultivators. Differences in SOC contents between treatments were dependant on tillage intensity, biomass production, and fertilization. In the 0-20 cm layer, the highest SOC contents occurred in the > 2000 mu m soil fraction that received 40 t ha(-1) farmyard manure every fourth year and the lowest SOC content occurred in the 53-250 mu m fraction in the unfertilized treatment. Manure application influenced SOC content and its distribution among soil aggregate fractions but did not affect water-stable aggregates. SOC was primarily enriched within the > 2000 mu m aggregates, so their turnover is essential for SOC preservation. The carbon management index was highest in 20-40 cm soil depth, which emphasizes the importance of deeper soil layers in SOC conservation. In conclusion, declining SOC levels are related to tillage practices which could not be compensated by fertilization or crop rotation.