Optimizing regional irrigation management in arid saline areas using a process-based hydro-salt-crop model and fallow strategy

Agriculture in arid regions faces water scarcity and spatially heterogeneous soil salinization, compelling consideration of brackish groundwater irrigation and strategic fallowing under conditions of extreme water scarcity. A key challenge for agricultural managers is optimizing limited surface and groundwater allocation in complex, heterogeneous saline environments with varying water availability. This study introduces a gridded regional irrigation water optimization model under total irrigation water control, integrating salt effects, fallow strategy and multi-source water management. The model: (1) incorporates salt impacts on crop growth, saline groundwater use, and spatial salt heterogeneity; (2) generates surface/saline groundwater allocation and marginal land use guidance; (3) balances water scarcity and salinization trade-offs. An empirical study was conducted using cotton field data in the First Division of the Tarim Irrigation District in Xinjiang, China. The results suggest that the optimized water allocation scheme could increase cotton lint yield in the Tarim Irrigation District by up to 9959 tons (+3.3 %) compared to traditional uniform allocation. Soil salt content dominated allocation decisions. When surface water availability is limited, water distribution should prioritize high-yield fields (non-severe salinization), and supplemental brackish groundwater irrigation can mitigate yield losses. Rational fallowing can enhance total yield in the irrigation district while reducing input costs, with severely saline areas being prime candidates for fallowing policies. This research provides a scientific basis for optimizing water-salt management in cotton production, groundwater extraction, and irrigation water allocation in saline arid regions, while future work could integrate ion-specific chemistry and its crop response functions for wider applications.