Application of the SWAP model to simulate the field water cycle under deficit irrigation in Beijing, China

The evaluation of the field water cycle under deficit irrigation plays an important role in studying mechanism of field water dynamics, optimization of agricultural water management strategies, and assessment of regional water resources. In this study, the agro-hydrological Soil–Water–Atmosphere–Plant (SWAP) model was used to evaluate the field water cycle for a winter wheat-summer corn double cropping system in Beijing, China under deficit irrigation. A carefully designed field experiment was carried out from 2007 to 2009 with six irrigation treatments. The SWAP model was calibrated with soil water contents of two treatments. The dataset of the main field water balance components including soil water content, profile water storage and water flux through the bottom of the root zone were used to validate the SWAP model. The average root mean square error (RMSE) and the mean relative error (MRE) values of predicted soil water contents were 2.4% and 8.0%, respectively. The dataset of predicted and measured values were close to the 1:1 scale line for both the profile water storage and soil water flux. As an application of the SWAP model, the optimal irrigation management practices for the hydrologic years of 75%, 50% and 25%, respectively, in the Beijing area were obtained. The simulated average amount of water saving and groundwater recharge under the optimal irrigation schedules were about 190 mm and 16.1 mm, respectively. This study indicates that the SWAP model can be used as a powerful tool to simulate the field water cycle and evaluate irrigation practices.