Optimizing a water-saving and salt-controlling irrigation strategy for improving cotton yield with the AquaCrop model under mulched drip irrigation in saline-alkali soil

Cotton was an important agricultural economic crop in the arid areas of Xinjiang, China, yet water shortage and soil salinization were two major facts restricting cotton production in Xinjiang region. Adopting efficient water-saving and salt-controlling strategies based on AquaCrop model would be a necessary measure to maintain the sustainable development of agriculture in Xinjiang. The objective of this study was therefore to optimize water-saving and salt-controlling strategies by combining the AquaCrop model with a 4-year field experiment conducted in southern Xinjiang from 2017 to 2020. Using the experiment data calibrated and validated the parameters of AquaCrop model, the results showed that the model was accurate in simulating the changes of cotton canopy coverage, soil moisture, electrical conductivity, biomass and yield (the coefficient of determination (R-2) >0.58, the index of agreement (d) >0.34). Based on the meteorological data from 1958 to 2017, AquaCrop model was used to simulate two scenarios of setting irrigation total amount and changing irrigation frequency (P1-P16), setting irrigation quota and changing irrigation frequency (P17-P32). The results showed that: (1) the total irrigation amount was 450 mm and irrigation once event every 5 days, the cotton yield and biomass reached maximum values of 5.78 and 14.75 t ha(-1), and the salt accumulation decreased by 7.63, 21.58, and 72.23% compared with the irrigation once event every 7, 10, and 13 days, respectively; (2) the irrigation quota was 36 mm and the irrigation once event every 7 days, yield and biomass reached maximum, the value were 5.73 and 14.63 t ha(-1), respectively. However, the salt accumulation was the lowest when the irrigation quota was 45 mm and the irrigation once event every 5 days. Based on scenario simulations, the relationship between irrigation amount and yield was fitted as a quadratic curve. In the southern Xinjiang region, the suitable irrigation amount for cotton covered with film mulch was 450 mm, and the irrigation once event every 5 days, which could ensure cotton yield while reducing soil salinization risk.