Evaluation of Soil-Water-Atmosphere-Plant (SWAP) model in vertisol under various tillage and nitrogen application rates using wheat as a test crop

The Soil-Water-Atmosphere-Plant (SWAP) model was evaluated for its sensitivity to various tillage systems and nitrogen application dosage in vertisol of Madhya Pradesh, India. The aim of this study was to assess the model’s performance in simulating soil water dynamics, crop growth, and impacts of nitrogen dosage under different management frameworks. Field experiments were carried out over two growing seasons with two tillage treatments (conventional tillage and no-tillage) and four nitrogen application rates (0, 60, 120, and 180 kg/ha) of the Recommended Dose of Fertilizer (RDF), which was set at 120 kg/ha. The SWAP model was calibrated using the Richards equation for soil water transport and validated against observed data. Sensitivity analysis revealed that the model was most sensitive to soil hydraulic parameters, particularly saturated hydraulic conductivity and soil water retention parameters. Tillage practices significantly affected model performance, with conventional tillage showing the best agreement between simulated and observed values indicated by Root Mean Square Error (RMSE)= 0.045 m³ m−³, R² = 0.87). Nitrogen application rates.180 kg N ha−¹ showed diminishing returns in model accuracy. The study demonstrates that the SWAP model can effectively simulate soil-water-plant interactions in vertisol under different management practices, providing valuable information for precision agriculture applications.