Soil organic carbon accumulation in organic cropping systems

How organic and conventional grain production systems under different tillage regimes affect total and biologically active soil organic carbon (SOC) accumulation is poorly understood as organic no-till systems were only developed in the past two decades. In this study, how long-term conventional and organic row-crop management under different tillage regimes affect soil organic carbon dynamics and aggregation was examined at the Rodale Institute’s Farming Systems Trial (FST) in Pennsylvania. The experiment includes three cropping system treatments which were initiated in 1981: (i) conventional (cropping systems which uses synthetic fertilizers and plant protection chemicals), (ii) organic-legume (organic cropping systems that use legumes as their nitrogen source), (iii) organic-manure (organic cropping systems that use manure plus leguminous cover crops as nitrogen sources); and two tillage treatments which were initiated in 2008: (i) conventional tillage and (ii) no-tillage. Organic-manure treatments were expected to maximize total and biologically active SOC accumulation. Soil samples were collected from three depth increments (0-10, 10-20 and 20-30 cm) in mid-June, 2018, and measured for total SOC and biologically active microbial biomass carbon, permanganate oxidizable carbon, and water-extractable carbon concentrations. Soils under organic-manure management had the highest and conventionally managed soils the lowest concentrations of total and biologically active SOC regardless of tillage regime. Additionally, no-tilled and organic systems, especially organic-manure systems, increased the proportion of large macroaggregates, wet aggregate stability, and SOC protection within macroaggregates. Therefore, organic and/or no-till management is regenerative by enhancing soil organic carbon accumulation and aggregate stability.