Whole agricultural-year modeling for irrigation strategies and crop responses in seasonally frozen regions

Efficient irrigation management is crucial for sustaining agricultural productivity under increasing water scarcity. In arid, seasonally frozen regions, irrigation practices extend beyond the crop season to include non-crop season (off-season) irrigation (e.g., autumn or pre-planting irrigation), where the presence of freeze-thaw processes further complicates soil water and salt dynamics and their influence on subsequent crop season conditions. Developing effective irrigation strategies in such regions requires an agricultural-year (agr-year) scale approach that integrates both freeze-thaw and crop growth periods within a unified framework. In this study, the SHAW-SC, an agr-year scale model with a fully coupled framework integrating heat-water-salt transport with crop growth, was enhanced to improve its capacity for irrigation management assessments. The improvements include (1) a lateral drainage dynamics module capturing subsurface flow and drainage-driven groundwater fluctuations, and (2) a quantitative crop emergence function linking seedling emergence to near-surface soil water-salt conditions. The enhanced model was validated against field observations of soil temperature, moisture, salinity, and crop growth for sunflower, spring wheat, and maize in the Hetao Irrigation District, northwest China. Scenario simulations were then conducted to evaluate agr-year irrigation management strategies by systematically varying autumn irrigation, crop season irrigation, and initial water table depth under drained-field conditions. The results also revealed that non-crop season irrigation is critical for securing crop emergence and mitigating crop stress, while also affecting agr-year crop water productivity through off-season evaporation losses. The improved SHAW-SC model offers a robust, physically based decision-support tool for sustainable irrigation planning in arid, seasonally frozen agroecosystems.