Soil Organic Carbon Dynamics in a Sod-Based Rotation on Coastal Plain Soils

A frequently used cropping system in the southeastern Coastal Plain is an annual rotation of cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.) under conventional tillage (CT). The traditional peanut-cotton rotation (TR) often results in erosion and loss of soil organic carbon (SOC). Incorporation of bahiagrass (Paspalum notatum Fluegge) into the peanut-cotton rotation for 2 yr (also called a sod-based rotation or SBR) has been suggested for improving SOC, particularly in conjunction with conservation tillage practices. To determine the effect of the SBR on carbon sequestration, SOC and its isotopic composition were evaluated on established (>10 yr) crop rotation systems. Cropping systems evaluated included (i) TR under CT, (ii) TR under strip tillage (ST), (iii) SBR under CT, (iv) SBR under ST, and (v) SBR under ST with cattle grazing. Total SOC, bahiagrass-derived SOC, and potential C mineralization increased in the top 10 cm of soil, indicating the potential for ST to improve soil fertility in SBR systems. Grazing bahiagrass decreased SOC in the 5 to 10 cm depth, but this effect was not observed for the subsequent peanut crop and did not appear to have a long-term negative effect on SOC storage. The SBR did not show consistent improvements in total SOC compared with the TR. A 3-yr comparison of SOC concentration revealed C increases in SBR and TR systems, indicating that other conservation practices (e. g., winter cover cropping) are the primary contributors to SOC storage for Coastal Plain soils evaluated in this study. Isotopic analysis of mineralized CO2 indicated bahiagrass-derived SOC may be preferred over C-3 crop-derived SOC for degradation.