Simulation of water balance in a maize field under film-mulching drip irrigation

Film-mulching drip irrigation technology has been widely promoted and used in arid regions. However, few studies have simulated the water balance process under film-mulching drip irrigation. In our study, the water movement in different soil layers and the distributions of evaporation and transpiration were evaluated using the HYDRUS-2D model. Long-term continuous observations of evapotranspiration, soil evaporation, crop transpiration and soil moisture in a maize field under film-mulching drip irrigation were conducted using an eddy covariance system, micro-lysimeters, stem-flow gauges and soil water sensors from 2014 to 2016 in northwest China. Experimental data were collected to calibrate and validate the model. Results showed that the accuracy of HYDRUS-2D was satisfactory in deep soil layers and that the RMSEs (root mean square errors) of the 20 cm, 40 cm, 60 cm and 80 cm soil layers were 0.022 cm(3) cm(-3), 0.018 cm(3) cm(-3), 0.014 cm(3) cm(-3) and 0.010 cm(3) cm(-3), respectively. Thus, the model could be improved to better simulate soil water in surface soil layers. The results suggest that HYDRUS-2D can generally be used to simulate the actual evaporation (Ea), transpiration (Ta) and evapotranspiration (ETa) in a maize field under film-mulching drip irrigation, with the REs (relative errors) of 1.7%, -11.06% and -8.27%, respectively. The simulation error of ETa mainly stemmed from the simulation error of Ta, and the error contribution was 91.02%. Therefore, further studies that consider the effects of film-mulching drip irrigation are needed to improve the root water uptake and the ET calculation modules and enhance the accuracy of the HYDRUS-2D model.