Simulation of soil water transport in apple-soybean intercropping system under drip irrigation and film mulching

Intercropping and mulched drip irrigation are widely used techniques for achieving high yields and water savings. Understanding the soil moisture distribution characteristics of intercropping farmland under mulched drip irrigation is crucial for improving water use efficiency, increasing yields, and boosting income. This study aimed to investigate soil moisture under different irrigation amounts and film mulching times through a two-year field experiment.In the experiment, two upper limits of irrigation amount (50% and 80% of field water holding capacity) and two film mulching times (soybean sowing to pod setting stage and film mulching throughout the growth period) were set. The HYDRUS2D model was used to simulate the difference in soil moisture at various positions and the two-dimensional distribution characteristics of soil moisture in intercropping drip irrigation farmland. The results showed that the soil moisture model based on HYDRUS2D had high precision, with a coefficient of determination ranging from 0.60 to 0.93 and a root mean square error ranging from 0.006 to 0.038 cm³/cm³. In the horizontal direction, the soil moisture content at 2.3 m from the tree row increased by an average of 4.87% to 17.65% compared to other distances. In the vertical direction, the maximum soil moisture content was observed in the 40 cm soil layer, with an increase of 26.04% to 42% compared to the 10 cm soil layer. The 2-D soil moisture distribution showed that the moisture saturation zone of drip irrigation was mainly concentrated in the 0-20 cm soil layer. These findings can serve as a reference for developing irrigation schedules for intercropping farmland under drip irrigation.