Long-Term Impacts of Cropland Management on Depth Distribution of Soil Organic Carbon in West Tennessee.

Cropland practices such as crop rotation, tillage, and cover crops can influence soil organic carbon (SOC) accumulation. In this study, three long-term field experiments: Rotation Experiment, Soybean Experiment, and Cotton Experiment) were conducted in Tennessee to understand the effect of cropland management on SOC and potassium permanganate oxidizable C (POxC). In the Rotation Experiment, six crop rotation treatments were established for 12 years including continuous corn, corn rotated with soybean, continuous soybean, soybean rotated with cotton, continuous cotton, and cotton rotated with corn. The Soybean Experiment is a continuous soybean system under three tillage treatments for 35 years: moldboard plow tillage, no-tillage, and no-tillage with winter wheat cover crop. The Cotton Experiment is a continuous cotton production system for 33 years, with cover crop treatments [no cover, hairy vetch, and winter wheat] and tillage treatments (no-tillage and conventional tillage). Results showed that analyzing soils at shallower depth increments can be an effective method to detect the response of SOC to cropland management. However, no management effect was observed when 0-15 cm was studied as a single layer. Rotation Experiment revealed that corn or cotton based systems had higher SOC than soybean based systems at 0-2.5, 2.5-5, 5-7.5, 7.5-10, and 10-15 cm. In Soybean Experiment, moldboard plow tillage had lower SOC than no-tillage systems at 0-2.5 and 2.5-5 cm. Compared to conventional tillage systems, the SOC in no-tillage systems was higher at 0-2.5 cm while lower at 5-7.5 and 7.5-10 cm in Cotton Experiment. The cover crop effect on SOC was found neither in Soybean Experiment nor in Cotton Experiment. Data across the three experiments showed that POxC was positively correlated with SOC (P < 0.0001, r² = 0.93). This study indicated that long-term adoption of management strategies on Tennessee croplands significantly impacts SOC and POxC in the shallow depth increments.