Quantifying the carbon sequestration potential of sorghum and the effects of tillage on soil carbon dynamics using the SWAT-C model at the watershed scale in the Texas High Plains, USA

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This study aimed to quantify the carbon sequestration potential of sorghum and assess tillage effects on Soil Organic Carbon (SOC) dynamics at the watershed scale in the Texas High Plains (USA) using the Soil and Water Assessment Tool-Carbon (SWAT-C) model. The model was configured using existing sorghum management practices, with conventional tillage as the baseline. Calibration (2016–2021) and validation (2022–2024) were conducted using a multisite approach in RSWAT, with monthly Soil Moisture Active Passive (SMAP) SOC data for two hydrologic response units representing sorghum and other agricultural land (AGRC). Conservation and zero tillage effects on SOC in sorghum fields were evaluated relative to conventional tillage. Model performance was satisfactory, with Percent Bias (PBIAS) <5.4%, Root Mean Square Error (RMSE) <2.83 t ha -1 and Mean Absolute Error (MAE) <2.35 t ha -1 . Simulated long-term annual mean SOC closely agreed with SMAP-derived SOC. SOC stocks across sorghum, AGRC, shrubland, and grassland were compared using one-way analysis of variance (ANOVA), while tillage effects were evaluated using a linear mixed-effects model. Sorghum had the highest long-term (2016–2024) mean SOC (47.80 ± 16.29 t ha -1 ), followed by AGRC (47.74 ± 15.48), shrubland (42.83 ± 19.62), and grassland (42.77 ± 19.76). Sorghum also showed better SOC, carbon sequestration, and total carbon stocks. Conservation and zero tillage generally increased SOC relative to conventional tillage, with conservation tillage showing the highest gains, although localized declines occurred. Overall, conservation tillage showed better potential to enhance carbon sequestration in sorghum fields, with spatially variable outcomes across the watershed.