Synergistic regulation of irrigation and drainage based on crop salt tolerance and leaching threshold

The implementation of current drip irrigation scheduling, which only considers crop water demands (referred to as empirical drip irrigation) during the growth period and uncontrolled leaching during fallow periods, exacerbates issues of soil salinization and water scarcity in the Xinjiang region. In pursuit of more scientifically effective irrigation and leaching methods, this study employed the H2DSWAP model coupled by the HYDRUS-2D and a Soil–Water–Atmosphere–Plant model (SWAP) for scenario experiments. Results showed that prolonged irrigation without drainage (winter-free irrigation) led to an annual upward trend in salt accumulation within the root zone (0–100 cm) through drip irrigation under film mulch. In regions with shallow groundwater levels (≤ 2.0 m), an exclusive focus on crop water requirements and neglecting leaching demands for salts led to a gradual reduction in crop yield, reducing by 86.8 % after 12 years of operation. Conversely, by considering both water and salt stress thresholds during the growth stage for irrigation, optimal crop yields can be maintained. However, salt predominantly accumulated within the 60–100 cm soil layer, inducing recurrent leaching during the growth period due to continual salt migration in this layer. This occurrence resulted in wasted water resources, uneven soil salt distribution, and ultimately diminished crop yields. The simulation findings for diverse winter irrigation scenarios suggested that the salinity content in the deep root zone (60–100 cm) could function as a leaching threshold for determining the necessity of winter irrigation, approximating a value of 11 g kg−1. In comparison to conventional irrigation and drainage practices, the irrigation and drainage coordinated regulation model proposed in this study contributes to salt removal, effectively restraining the waste of water resources caused by frequent winter irrigation.