Irrigation scheduling in sand-layered farmland: Evaluation of water and salinity dynamics in the soil by SALTMED-1D model under mulched maize production in Hetao Irrigation District, China

Issues of water scarcity and uneven spatiotemporal distribution are becoming increasingly prominent in arid and semi-arid regions. As the largest single head system irrigation district in Asia, the Hetao Irrigation District in Inner Mongolia has a widespread distribution of farmland with sand layers along the Yellow River. However, timely and appropriate irrigation reliability rate is low; hence, assessing irrigation benefits for sandy soil farmlands is crucial. This study used experimental monitoring data from the 2020–2021 maize growth period in a typical sand layer farmland and a modified SALTMED model with adjusted dual crop coefficients (Kcb adj and Ks) to simulate soil water and salt movement, crop growth, water consumption patterns, and yield accumulation processes. The goodness-of-fit indicators of the SALTMED model simulation values and the observed values were within a reasonable range. In the normal water year, the actual crop evapotranspiration during the spring maize growing season was 566 mm, which was 89.1% of the potential crop evapotranspiration. In the dry year, these values were 571 mm and 88.4%, respectively, with a 6.0% decrease in yield from that of the normal water year. When irrigation was delayed by 1–7 days and the irrigation depth was within 224–267 mm, the capillary barrier effect of the sand layer enabled water conservation in the root zone while increasing water productivity by 5.15–9.95% (dry grain weight) and 4.68–10% (fresh grain weight). Therefore, given the context of water scarcity, by implementing a reasonable irrigation schedule, it is possible to adjust the soil water and salt environment of farmland with a sand layer in the irrigation area, thereby improving crop yield and crop water productivity.