Understanding Soil Water and Salt Transport of Winter Wheat under Irrigation with Brackish Water in Coastal Saline Region using HYDRUS-2D

Inappropriate brackish water irrigation can severely affect crop growth and significantly reduce land quality. Analyzing soil water and salt transport and understanding the relationship between salt stress (SS) levels, desalination rate (DR, %), and crop growth is essential to develop optimal brackish water irrigation strategies. This study applied the HYDRUS-2D model to simulate dynamic changes of soil water and salt in the 0–100 cm soil layer of a coastal saline region in winter wheat fields. Calibration and validation with field-measured soil water content (SWC) and soil salt content (SSC) showed a good agreement between simulated and measured values. Eight irrigation schemes were evaluated for the critical fertility period (from heading to harvesting) of winter wheat, including two irrigation rates 60 mm (S1), 75 mm (S2) and four mineralization levels of brackish water 1 g·L −1 (G1), 2 g·L −1 (G2), 3 g·L −1 (G3) and 4 g·L −1 (G4). The results showed that higher brackish water mineralization prolongs salt stress and reduces DR. SWC varied less in different brackish water irrigation schemes, and SSC tended to increase in all 0–40 cm, while it tended to decrease in all 60–100 cm. For the same mineralization scenario, S1 had a higher DR and a shorter medium SS duration than the S2 scenario. Throughout the simulation period, high SS occurred only in the S1G4 and S2G4 schemes, while no high SS occurred in the remaining irrigation schemes. It was concluded that 60 mm irrigation quantity and brackish water with salinity not greater than 3 g·L −1 was the optimal strategy for the investigated region. The research findings are derived from insights gained through soil water and salt simulation results during the critical growth stages of winter wheat under a single irrigation event, while broader long-term recommendations necessitate further investigation.