Water-Quality-Integrated Optimal Allocation of Agricultural Water Resources in Arid Irrigation Districts: A Case Study of Yingjisha County, Xinjiang

We developed a comprehensive water-quality-integrated model for allocating agricultural water resources in Yingjisha County, a hyper-arid county in Xinjiang, China. Groundwater was classified into four salinity levels, and brackish water was incorporated into the irrigation water supply system according to crop salt tolerance. The objective was to maximize agricultural net profit, while accounting for the Maas–Hoffman yield reduction coefficient, a graded salt damage penalty, and soft-constraint penalties, subject to constraints on water quantity, water quality, land area, food security, and freshwater conservation. Under the graded penalty framework, low-salinity brackish water remained economically viable for irrigation: freshwater dependency was governed by the freshwater-conservation ratio, gross agricultural profit increased by 13.6–17.0%, and the time to onset of mild soil salinization reached 5.7–6.0 years under the corrected per-class constraints. These results demonstrate the feasibility of classified regulation for brackish water irrigation in arid irrigation districts.