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

Authors: Abrahamson Beese, Deborah; NORFLEET, M - USDA-NRCS; CAUSARANO, H - AUBURN UNIVERSITY; WILLIAMS, J - TEXAS A&M UNIVERSITY; SHAW, J - AUBURN UNIVERSITY; Franzluebbers, Alan

Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2007
Publication Date: 3/1/2007
Citation: Abrahamson Beese, D.A., Norfleet, M.L., Causarano, H.J., Williams, J.R., Shaw, J.H., Franzluebbers, A.J. 2007. Effectiveness of the soil conditioning index as a carbon management tool in the southeastern USA based on comparison with EPIC. Journal of Soil and Water Conservation 62:94-102.

Interpretive Summary: Various models are being developed and utilized by scientists and government agencies to quantify the potential for carbon storage in soil. Soil carbon storage could reduce greenhouse gas emissions and help avoid global warming. Testing of models is needed to verify their accuracy and reliability. A collaboration among scientists from the USDA-Agricultural Research Service in Watkinsville Georgia, USDA-Natural Resources Conservation Service, Auburn University, and Texas A&M University tested the performance of a highly technical, environmental model (EPIC v. 3060) against a simple predictive model currently used by the USDA-Natural Resources Conservation Service to identify soil management systems that might contribute to improved soil quality. Several cotton management systems were evaluated at three locations (Blackland Prairie in Texas, Southern Coastal Plain in South Carolina, and Southern Piedmont in Georgia). Both models predicted low soil quality with conventional tillage production of cotton without a cover crop (traditional management), but higher soil quality with no-tillage management of cotton with winter cover crop and/or rotation with other high-residue producing crops. Both models will be of great importance to land managers and policy makers to improve soil quality on the 7 million acres of cotton in the southeastern USA, although there is still an urgent need to collect field-based measurements of soil quality in conservation management systems to fully validate these tools.

Technical Abstract: Sequestration of soil organic carbon (SOC) in the southeastern USA is perceived as occurring at a relatively low rate, because of the inherent low SOC content of most agricultural soils. However, recent field estimates of SOC sequestration in conservation management systems suggest that the sequestration rate could be higher than in other regions of the country. We used the EPIC v. 3060 model and the soil conditioning index (SCI) to estimate long-term SOC storage at Temple TX, McColl SC, and Watkinsville GA using four management systems: (a) cotton (Gossypium hirsutum L.) with conventional tillage, (b) cotton with no tillage, (c) corn (Zea mays L.)–cotton rotation with no tillage, and (d) 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 averaged 0.46 Mg/ha/yr under the three no-tillage management systems and -0.03 Mg/ha/yr under conventional tillage with EPIC. The SCI also predicted a strong difference in SOC sequestration 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 EPIC were related to the SCI, but not necessarily in a linear manner as previously suggested. Cotton lint yield with no tillage averaged 88% of yield with conventional tillage, but lint water-use efficiency was not different between tillage systems. Under the simulated management and environmental conditions selected, the SCI appears to be a valuable method for making reasonable, cost-effective estimates of potential SOC sequestration in the southeastern USA, although validations under actual field conditions are still needed.