Soil conditioning index and soil organic carbon in the Midwest and southeastern United States

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 United States. We found that SOC sequestration (at 25 ± 6 cm [10 ± 2 in] depth) 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 tn ac⁻¹ SCI⁻¹), which translated into a rate of 0.35 ± 0.06 Mg C ha⁻¹ y⁻¹ SCI⁻¹ (314 ± 57 lb ac⁻¹ yr⁻¹ SCI⁻¹), which is the mean ± standard error of 18 slope estimates. Calibration slopes did not vary significantly between the Midwest and southeastern United States, resulting in a combined calibration of 0.29 ± 0.03 Mg C ha⁻¹ y⁻¹ SCI⁻¹ (255 ± 30 lb ac⁻¹ yr⁻¹ SCI⁻¹), which is the 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.