Long-Term Impacts of Conservation Tillage, Cover Cropping, and Nitrogen Application on Carbon Storage Potential Under Cotton Production in West Tennessee.

Conservation soil management practices influence the biogeochemical cycling of carbon (C) in soil. Specifically, the microbial decomposition of soil organic C (SOC) can be a major determinate of both C-loss via respiration and long-term storage in agroecosystems. Our objective is to examine SOC stability in an agroecosystem under various conservation practices (tillage, cover cropping, and nitrogen application rate). We measured respiration rates from long-term incubations for 424 days. Data were fit to exponential models of SOC decomposition to calculate the size and turnover time of multiple pools of SOC and compared to total SOC. In fertilizer N treatments, mean SOC remaining after 424 days ranged from 9.1±0.8 to 11.4±1.4 mg C g^-1 dry soil. No-tillage plots had significantly greater SOC than conventional tillage (10.8 ±1.2 and 9.4±0.8 mg C g^-1 dry soil, respectively). Organic inputs from vetch cover cropping with conventional tillage result in 31% more C being stored in the labile SOC pool compared to no cover cropping with conventional tillage. In contrast, fertilizer N addition resulted in more C in the intermediate SOC pool compared to controls. These results suggest that C-loss is primarily dependent on N form and content, and perhaps secondarily by physical factors that occur with reduced tillage. We don’t know if these differences are driven by functional differences in the microbial community, or by the physiochemical composition of SOC.