Soil water/salt balance and water productivity of typical irrigation schedules for cotton under film mulched drip irrigation in northern Xinjiang

Film mulched drip irrigation (FMDI) has clear benefits for saving water and promoting cotton production in Xinjiang, China. Due to the complicated transport processes for soil water and salt under FMDI, it is still challenging to systematically answer the questions such as the soil water and salt balance in the root zone, cotton yield and water productivity (WP) under typical planting modes and irrigation schedules. Previously, we proposed a HYDRUS-2D model with modified root water uptake (RWU) function and simulated the two-dimensional soil water flow and solute transport in cotton fields under FMDI, but we ignored the effects of the cotton yield and WP. From the perspective of smart irrigation, it is necessary to evaluate the effects of irrigation on crop production, WP, and soil environments. Thus, in the present study, our HYDRUS-2D model coupled with a validated crop water production function was applied to evaluate the effects of typical irrigation schedules and the antecedent soil salinity distributions on the soil water/salt balance, and plant water status, and leaching fraction, as well as the cotton yield and WP under FMDI in 36 scenarios. These scenarios included two antecedent soil salinity distributions (AS), six irrigation amounts (IA) and three irrigation intervals (IF). Compared with the lower AS scenarios, the higher AS scenarios obtained lower cotton transpiration and evapotranspiration but higher evaporation, drainage, and soil water storage, and the crop water status and leaching fraction were also increased due to the soil salt stress restricting RWU. The salt balance results indicated the current irrigation scheduling under FMDI leads to desalination processes in different scenarios. Moreover, the cotton yield and the corresponding WP for cotton (WPETₐ) and irrigation (WPI) were estimated. Under different AS scenarios, binary quadratic regression equations were developed based on IA and IF data to predict the cotton yield, WPETₐ, and WPI. Appropriate irrigation strategies are recommended based on the results. Our results could provide a scientific basis for optimizing irrigation schedules and improving the understanding of irrigation management under FMDI among local farmers in Xinjiang.