Effectiveness of the soil conditioning index as a carbon management tool in the southeastern USA based on comparison with EPIC

Models are being developed and utilized by scientists and government agencies to quantify the potential for carbon storage in soil. The Environmental Policy Integrated Climate (EPIC) v. 3060 model is a process-based model requiring detailed inputs. The soil conditioning index (SCI) is a simpler tool to predict relative change in soil organic carbon (SOC) using table values for three management components (i.e., organic matter, field operations, and erosion) within the framework of the Revised Universal Soil Loss Equation 2 model. Our objective was to determine whether SOC sequestration from no-tillage cropping systems in the southeastern USA could be simply predicted with SCI compared with detailed simulations using EPIC. Four management systems were evaluated: (1) cotton (Gossypium hirsutum L.) with conventional tillage, (2) cotton with no tillage, (3) corn (Zea mays L.)-cotton rotation with no tillage, and (4) bermudagrass (Cynodon dactylon L.)-corn-cotton rotation with no tillage. All no-tillage systems used wheat (Triticum aestivum L.) as a cover crop. Simulated SOC sequestration with EPIC was 0.46 ± 0.06 Mg ha-1 yr-1 (410 ± 51 lb ac-1 yr-1) under the three no-tillage management systems and -0.03 Mg ha-1 yr-1 (-30 lb ac-1 yr-1) under conventional tillage. The SCI also predicted a strong difference in SOC between conventional and no tillage. Differences in SOC sequestration among crop rotations were not readily apparent with EPIC but were with SCI. Predictions of SOC sequestration with SCI were comparable to those with EPIC but not necessarily in a linear manner as previously suggested. The SCI appears to be a valuable method for making reasonable, cost-effective estimates of potential changes in SOC with adoption of conservation management in the southeastern USA, although validations under actual field conditions are still needed.