Evaluating soil organic carbon sequestration potential in the Cotton Belt with the soil conditioning index

Abstract

Simulation models that are sensitive to management, edaphic factors, and climate could provide insights into how land owners and producers might be able to sequester soil organic carbon (C) and engage in emerging carbon markets. In this study, the soil condition- ing index (SCI) embedded in the Revised Universal Soil Loss Equation (RUSLE2) model was used to predict (1) potential soil organic C sequestration under conventional and conser- vation management of a diversity of cotton cropping systems throughout the Cotton Belt and (2) relative influences of soil texture, slope, climatic conditions, and management on potential soil organic C sequestration. Across 10 regions of the Cotton Belt, SCI scores ranked in the following order: perennial pasture > no-till cropping systems > conventional tillage cotton. Variations in significance of SCI scores occurred among 5 different no-till cropping systems within regions of the Cotton Belt. For example, 7 of the 10 regions had significantly (p ≤ 0.05) greater SCI scores (linked to greater soil organic C sequestration) when monoculture cotton was grown with winter cover crop than without. Variation in SCI was dominated by management (46%) and slope (24%) and very little affected by climate (7%) and soil tex- ture (1%). Increasingly wetter climatic conditions (as expressed by increasing precipitation to potential evapotranspiration) had a negative influence on SCI scores for all management systems and land slopes evaluated, but particularly for moldboard-plowed cotton on sloping land. With a linear relationship between SCI and soil organic C sequestration, predicted soil organic C sequestration averaged −0.31 ± 0.19 Mg C ha -1 y -1 (−280 ± 170 lb ac -1 yr -1 ) under conventionally tilled cotton, 0.12 ± 0.06 Mg C ha -1 y -1 (103 ± 52 lb ac -1 yr -1 ) under various no-till crop rotations, and 0.26 ± 0.02 Mg C ha -1 y -1 (231 ± 20 lb ac -1 yr -1 ) under perennial pasture. Cotton production with conventional tillage could only be expected to maintain soil organic C under a best-case scenario and would lose substantial soil organic C under most other scenarios. Simulations showed the strong, positive influence that conservation agricul- tural management has to sequester soil organic C, irrespective of climate, slope, and texture.