Simulation of crop water use of drip-irrigated summer soybean using the SIMDual_Kc model: A case study from Southern Xinjiang, China

Water scarcity in arid regions demands reliable estimation of crop evapotranspiration components. This study aimed to evaluate the applicability and simulation performance of the SIMDual_Kc model in estimating soil water balance, soil evaporation ( E ), crop transpiration ( T ), and evapotranspiration ( ET c ) of drip-irrigated summer soybean in the arid region of southern Xinjiang. A two-year field experiment (2024–2025) was conducted with four drip irrigation levels (W 75 , W 100 , W 125 , and W 150 ). Actual soil evaporation was measured using micro-lysimeters combined with the soil water balance method. Based on these observations, the SIMDual_Kc dual crop coefficient model was established, calibrated, and validated to simulate soil moisture dynamics and evapotranspiration components of summer soybean under different irrigation regimes. The results showed that for soil moisture dynamics, the coefficient of determination ( R 2 ) between observed and simulated values ranged from 0.626 to 0.896, the index of agreement ( d ) ranged from 0.873 to 0.943, the root mean square error ( R MSE ) ranged from 0.014 to 0.023 (m 3 ·m −3 ), and the Nash–Sutcliffe efficiency ( N SE ) ranged from 0.356 to 0.858; for soil evaporation, R 2 values ranged from 0.736 to 0.997, the index of agreement ranged from 0.408 to 0.787, the R MSE ranged from 0.369 to 0.914 (mm·day −1 ), and the N SE ranged from 0.515 to 0.912; for evapotranspiration ( ET c ) and transpiration ( T ), the R 2 values ranged from 0.857 to 0.997, the R MSE ranged from 3.549 to 17.478 mm, and the N SE ranged from 0.745 to 0.988. These results indicate that the SIMDual_Kc model can accurately simulate soil water balance and evapotranspiration components of summer soybean, exhibiting good applicability and stability. Based on model calibration and prediction, the SIMDual_Kc parameters suitable for drip-irrigated summer soybean in southern Xinjiang were identified as follows: the initial basal crop coefficient ( K cb,ini ) was 0.24, the mid-season basal crop coefficient ( K cb,mid ) was 1.15, and the end-season basal crop coefficient ( K cb,end ) was 0.52; the soil evaporation layer depth ( Z e ) was 0.11 m, and the readily evaporable water ( REW ) was 11 mm. These findings provide a scientific basis for optimizing irrigation strategies and improving water use efficiency of summer soybean in arid regions.