Applicability of the Aquacrop model in optimization of irrigation and salt leaching schedule during the reproductive period of cotton in Northern Xinjiang of China

China's most fabulous cotton-producing area is Xinjiang. In Xinjiang, soil salinization and water shortage are now the two key challenges limiting agricultural productivity and sustainable growth. Water wastage and secondary soil salinization in the area are still being made worse by irrational irrigation during the growth period and salt leaching during the off-growing period. A breakthrough in solving these problems is the development of sensible irrigation and salt-leaching techniques throughout the growing period to preserve water efficiently, cut expenses, and guarantee cotton crop yields. Following calibration of the model parameters and validation using field experiment data from 2020 and 2021, respectively, the optimal scheduling of cotton field irrigation and salt leaching was investigated to clarify the applicability of the Aquacrop model to the growth and production of simulated cotton fields under membrane and subsurface drip irrigation in northern Xinjiang. Then the calibrated model was used to reveal the effects of three irrigation levels (100%ETc (D₁), 80%ETc (D₂), and 60%ETc (D₃)), three salt leaching amounts (0 (Q₁), 120 mm (Q₂), and 240 mm (Q₃)), three irrigation frequencies (5 (F₁), 7 (F₂), and 10 d/time (F₃)) and three types of precipitation year (rainy years(H₁), normal years (H₂), and dry years (H₃)) on cotton yield and irrigation water productivity. The results showed that canopy cover, aboveground biomass NRMSE (Normalized root mean square error)≤20.998%, d (Index of agreement)≥0.967, and R² (Coefficient of determination)≥0.914 for all treatments in 2021, and yield RMSE, NRMSE, d, and R² were 0.389 t/hm², 6.797%, 0.836, and 0.754, respectively, and the model simulated well overall. Model simulations based on 58 years of meteorological data showed that the effects of irrigation level, salt leaching quota, and precipitation year type on cotton yield and irrigation water productivity were statistically significant, and irrigation frequency effect was not significant; in the cotton planting area with average soil salinity ranging from 12 to 18 g/kg, accounting for yield, irrigation water productivity, and actual production, the total irrigation and salt leaching quota of 80% ETc+120 mm (D₂Q₂) was recommended for rainy years, and the total irrigation and salt-leaching quota of 100% ETc+120 mm (D₃Q₂) was recommended for both normal and dry years; it was suggested that the irrigation frequency be increased to 10 d/time to reduce the frequency of irrigation and save costs. The optimal irrigation and salt leaching strategy proposed in this study was limited by model function and evaluation perspective. It was based on water conservation and optimal yield in cotton fields and did not consider the desalination conditions of membrane and subsurface drip irrigation. To develop more rigorous and convincing irrigation and salt leaching strategies, the Aquacrop model must be coupled with other water and salt transport models to improve the model's functionality and comprehensively assess soil desalination and cotton field production conditions.