Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2012
Publication Date: 9/10/2012
Citation: Franzluebbers, A.J., Hubbs, M.D., Norfleet, M.L. 2012. Evaluating soil organic C sequestration in the Cotton Belt with the soil conditioning index (SCI). Journal of Soil and Water Conservation. 67:378-389. Interpretive Summary: Soil organic carbon sequestration can be a significant driver of how conservation management systems are adopted by producers and promoted by government agencies. Modeling of various tillage, crop rotation, and cover cropping conditions across the cotton growing region of the southeastern USA would allow us to assess the relative importance of soil type, climatic conditions, and management on soil organic carbon sequestration potential in the region. Scientists from USDA-ARS in Watkinsville, Georgia and USDA-NRCS in Temple, Texas and Washington, DC estimated potential soil organic carbon sequestration under conventional and conservation management of cotton cropping systems in each county throughout the Cotton Belt using the recently calibrated soil conditioning index. Soil organic carbon was predicted to decline with conventional tillage in most regions of the Cotton Belt, except the Desert Southwest region. Any decision to continue farming with conventional tillage is also risky for soil loss from erosion on all but the flattest parcels of land. Soil organic carbon was predicted to increase (modestly to significantly) using a variety of crop sequences with no-tillage management in all regions of the Cotton Belt. Adding winter cover crops to the crop sequence was beneficial to organic matter input and subsequent estimate of soil organic carbon sequestration. Simulations were most sensitive to management and slope variations and much less affected by climate and soil textural variations. These results have important implications for the sustainable management of the 4.2 Mha of cotton land in the southern USA.
Technical Abstract: Simulation models that are sensitive to management, edaphic factors, and climate could provide insightful probes of how land owners and producers might be able to sequester soil organic C and engage in emerging carbon markets. We used the soil conditioning index (SCI) embedded in the RUSLE2 model to predict (1) potential soil organic C sequestration under conventional and conservation 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 followed the order: perennial pasture > no-tillage cropping systems >conventional-tillage cotton. Variations in significance of SCI scores occurred among five different no-tillage cropping systems within regions of the Cotton Belt. For example, seven 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 texture (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/yr under conventionally tilled cotton, 0.12 +/- 0.06 Mg C/ha/yr under various no-tillage crop rotations, and 0.26 +/- 0.02 Mg C/ha/yr 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 agricultural management has to sequester soil organic C, irrespective of climate, slope, and texture.