Modeling the impact of irrigation thresholds on cotton yield in Northern Xinjiang using a field-calibrated CROPGRO-cotton model

Xinjiang’s cotton production constitutes > 90% of China’s total output, accounting for a significant proportion of the region’s agricultural water consumption. Setting suitable upper and lower irrigation thresholds during the reproductive period is critical for sustaining yields and promoting long-term sectoral sustainability. We integrate field experimentation and modelling techniques to evaluate cotton growth and yield responses to specified irrigation boundaries under mulch drip irrigation, with the aim of optimizing water use during key reproductive phases while maintaining stable yields. The calibrated CROPGRO-Cotton model was validated using data from fully irrigated and deficit-irrigated field trials conducted in 2023 and 2024. Thirty combinations of upper and lower irrigation limits were simulated for the flowering and boll setting period. Analyses identified optimal irrigation strategies to maximize seed cotton yield under drip irrigation systems. Precise regulation of irrigation limits increased cotton canopy height and seed yield by 1.08%-30.91% and 4.32%-32.45%, compared with local conventional drip irrigation practices. The model demonstrated high fidelity in replicating dynamic canopy height ( R 2 > 0.90, d > 0.85) and seed cotton yield (absolute relative error < 12%) under mulch drip conditions. Based on field experiments and the flowering and boll setting period model simulation results, for the reproductive period of cotton, optimal irrigation range limits in the seedling period should be 60%-100% field capacity (FC), 70%-85% FC in the squaring period, and 65%-90% FC in the flowering and boll setting period; pre-emergence irrigation of 25 mm and no irrigation should be applied in the boll opening period. These insights provide a valuable reference for deploying precision irrigation strategies in cotton cultivation across Northern Xinjiang.