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In order to explore the reasonable groundwater depth under current condition of water-saving implementation in Hetao Irrigation District, the SWAP (Soil-Water-Atmosphere-Plant) model was calibrated and validated based on field experiments data of spring maize in 2019 and 2020. The SWAP model was used to simulate soil water-salt flux and water-salt balance for 0–100 cm soil layer under current condition of groundwater depth, soil water-salt balance for 0–100 cm soil layer under different groundwater depth scenarios after model calibration and validation. The results showed that soil water flux cumulant of 0–100 cm soil layer was 111.6 mm and 63.1 mm during the two-year simulation periods under current condition of groundwater depth, respectively. Soil salt flux cumulant of 0–100 cm soil layer was −10.3 mg·cm −2 and −11.1 mg·cm −2 during the two-year simulation periods under current condition of groundwater depth, respectively. Soil salinity increased by 7.7 mg·cm −2 and 6.9 mg·cm −2 in 0–100 cm soil layer during the whole growth periods of spring maize under current condition of groundwater depth in 2019 and 2020, respectively. It had a risk of soil secondary salinization under current condition of groundwater depth in study area. It was necessary to regulate the groundwater depth to reduce soil secondary salinization. The simulation results of soil water-salt balance under different groundwater depth scenarios showed that when the average groundwater depth was about 1.96 m, it was conducive to crop growth and avoided soil secondary salinization. It was the appropriate groundwater depth under the condition of spring maize water-saving irrigation in study area. The underground pipe drainage system can be used to reduce the average groundwater depth to below 1.96 m, and the risk of soil secondary salinization is slight in study area.
Yuan et al. (Sat,) studied this question.