Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/13/2010
Publication Date: 5/30/2011
Citation: Franzluebbers, A.J., Causarano, H.J., Norfleet, M.L. 2011. Soil conditioning index (SCI) and soil organic carbon in the Midwest and southeastern USA. Journal of Soil and Water Conservation Society. 66:178-182. Interpretive Summary: Rapid and reliable assessments of the potential of various agricultural management systems to sequester soil organic carbon are needed to promote conservation and help mitigate greenhouse gas emissions. A collaborative effort to calibrate soil conditioning index (SCI) scores against soil organic carbon sequestration was developed among scientists with USDA-Agricultural Research Service in Watkinsville GA, National University in Asuncion Paraguay, and USDA-Natural Resources Conservation Service in Temple TX. Published soil organic carbon from long-term field studies throughout the Midwest and southeastern USA were compared with simulations run by the SCI under the umbrella of the Revised Universal Soil Loss Equation (RUSLE2). Across studies, soil organic carbon content increased by 0.435 metric tons of CO2 per acre per year per unit change in SCI. The calibration did not differ significantly between the Midwest and southeastern USA regions. These results will have important implications for farmers, crop advisors, scientists, and policy makers interested in carbon trading schemes throughout the 330 million acres of cropland in the USA.
Technical Abstract: Calibration of the soil conditioning index (SCI) to a diversity of field studies with known changes in soil organic carbon (SOC) would improve the usefulness of the SCI by the USDA–Natural Resources Conservation Service to assess the environmental services provided by agricultural land stewardship. Our objectives were to (1) calibrate SCI scores against SOC from published field studies in the Midwest and (2) compare the calibration with a recently derived calibration from the southeastern USA. We found that SOC sequestration (at 25 + 6 cm depth; 10 + 2 inches) could be reliably related to SCI across a diversity of studies in the region using the regression slope: 4.52 Mg C ha-1 SCI-1 (2.02 ton acre-1 SCI-1) [which translated into a rate of 0.35 + 0.06 Mg C ha-1 yr-1 SCI-1 (314 + 57 lb acre-1 yr-1 SCI-1; mean + standard error of 18 slope estimates)]. Calibration slopes did not vary significantly between the Midwest and southeastern USA, resulting in a combined calibration of 0.29 + 0.03 Mg C ha-1 yr-1 SCI-1 (255 + 30 lb acre-1 yr-1 SCI-1; mean + standard error of 49 slope estimates). The calibration of SCI scores to SOC will allow SCI to become a quantitative tool for natural resource professionals to predict SOC sequestration for farmers wanting to adopt conservation practices.