A Hydrus–AquaCrop Coupling Modelling Approach for Optimizing Irrigation Strategies of Cotton in Xinjiang Salinized Farmland

ABSTRACT

A critical challenge hindering the development of optimized irrigation schedules for crops is the difficulty in quantifying the coupled relationships among soil water, salinity and crop growth. Here, we integrated the Hydrus and AquaCrop models to develop a coupled modelling framework that captures the dynamic interactions between water, salt and crop growth, achieving high simulation accuracy for soil moisture ( R ²  = 0.75), soil salinity ( R ²  = 0.79), crop leaf area index growth ( R ²  = 0.95) and yield ( R ²  = 0.98). The results revealed that soil electrical conductivity (EC _e ) exceeding 7 dS·m ⁻¹ significantly inhibited cotton yield. The thresholds for irrigation water salinity were quantified for farmlands with varying degrees of salinization, alongside the optimal total irrigation amount (400 mm) and corresponding irrigation frequencies. Irrigation water salinity above 4.3 dS·m ⁻¹ markedly reduces cotton yield, whereas salinity levels ≤ 2.3 dS·m ⁻¹ promote salt leaching. The optimal irrigation frequencies that reconcile water–salt regulation and yield are 12–14, 10–14 and 8–10 irrigation events for lightly, moderately and severely salinized soils, respectively. This study clarifies the synergistic effects of irrigation amount, water quality and irrigation frequency on cotton growth, providing a theoretical framework for improving cotton water use efficiency in salinized fields.