Calibration and Validation of ADAPT and SWAT for Field-Scale Runoff Prediction

The pollutant reduction possible with a given agricultural best-management practice (BMP) is complex and site-specific. Water-quality models can evaluate BMPs, but model results are often limited by the lack of calibrated parameters for a given BMP. This study calibrated runoff prediction of two models (ADAPT and SWAT) for individual field plots having one till and two no-till management practices. The factors used for runoff calibration were curve number II (CN(II)) and saturated hydraulic conductivity (Ksat) for ADAPT, and CN(II), Ksat, and available water capacity for SWAT. Results were evaluated using coefficient of determination (R2), Nash-Sutcliffe efficiency (E(f)), root-mean square error, median-based E(f), and sign tests. Results indicated that for ADAPT, the best-fit CN(II) was 66 for the NT/SB (no-till plot with surface-broadcast fertilizer) treatment, 68 for the NT/DB (no-till with deep-banded fertilizer) treatment, and 70 for the tilled plot, whereas for SWAT the best-fit CN(II) was much higher, 86, for all treatments. Neither agreed with the textbook CN(II), 78, for sorghum in silty clay loam soil. The best-fit model parameters for both runoff calibration phases had excellent correlation to monthly totals and moderate correlation to individual events.