Long-Term Soil Organic Carbon Changes as Affected by Crop Rotation and Bio-covers in No-Till Crop Systems

Abstract

Soil organic carbon (SOC) sequestration is a potential negative-feedback for climate-warming gases in agriculture. The rate of no-tillage SOC storage is not well known due to large temporal and spatial biogeochemical and management variations. Therefore our objective was to compare long-term SOC fluxes at a no-till field site in Milan, Tennessee on Oxyaquic Fragiudalfs, in a split-block design with four replications. The whole-block was cropping sequences of corn, soybeans, and cotton with split-block bio-cover treatments of: winter wheat, hairy vetch, poultry litter, and a fallow control. Soil carbon flux was calculated at soil surfaces (0-5 cm) for years-0, 2, 4, and 8. During the first 2 years, small annual losses occurred in carbon over all treatments (1.40 Mg ha(-1)). During this time, cotton sequences lost significantly more surface SOC than other rotations. However, by year-4, SOC began to stabilize. By year-8, sequences with high frequencies of soybean and with greater temporal complexity generally gained greater SOC levels at 0-5 cm. Also, poultry litter bio-cover gained more surface SOC compared to wheat, vetch and fallow covers. Across all sequences and bio-covers, SOC had increased 1.47 Mg ha(-1) after 8 years from pre-experimental levels of 9.20 Mg ha(-1); suggesting long-term beneficial effects on C storage under no-till and diverse cropping sequences.