Evaluating the fate and variability of soil organic carbon and nitrogen species under conservation practices in the Raccoon River Watershed

Abstract This study evaluates the fate and variability of soil organic carbon (SOC) stocks and nitrogen species using the latest version of the Soil and Water Assessment Tool–Carbon (SWAT‐C) and assesses how conservation practices influence their dynamics in the Raccoon River Watershed (RRW). Dominated by intensive agricultural production, the RRW is a significant contributor of sediment and nutrient loads to local rivers and the Mississippi River. This SWAT‐C model simulates the export of SOC and nitrogen species and evaluates their responses under varying management scenarios. Model calibration was performed for streamflow, sediment, nitrate, total nitrogen, and organic carbon with monitoring data at both a sub‐basin and the watershed outlet. The SWAT‐C model achieved satisfactory to very good performance, with Nash–Sutcliffe efficiency values of 0.76–0.80, coefficients of determination ( R 2 ) of 0.78–0.86, and percent bias ranging from –18% to 12%. We assessed the effects of three conservation practices on SOC and nitrogen fate and transport: no‐till, residue harvest with cover crop implementation, and residue harvest without cover crops. The SWAT‐C results were compared with a historical baseline to quantify changes in the carbon and nitrogen loadings associated with each practice. This study highlights the role of conservation management and provides valuable insights for improving water quality and carbon sustainability in intensively farmed regions.