Optimizing the strategies of mulched brackish drip irrigation under a shallow water table in Xinjiang, China, using HYDRUS-3D

Optimizing mulched drip irrigation (MDI) with brackish water, which would benefit both soil and cotton yields, is crucial for arid areas lacking fresh water (FW) resources and having shallow brackish groundwater (BW). The HYDRUS-3D model, simulating three-dimensional soil water and salinity movement, was used to understand better MDI’s effects on the soil environment with shallow groundwater and optimize its operations. Optimized irrigation water amounts varied from 478.5 to 669.9 mm when salt concentrations of irrigation water were 1.01 g/L for FW and 3.0 g/L for BW, reflecting local surface water and groundwater qualities. Irrigation water consumption was evaluated and compared with literature results. The results showed that increasing irrigation frequency reduces water stress more than increasing irrigation water amounts. The low salinity area under the dripper expanded with an increase in the irrigation water amount and decreased with an increase in water salinity. Cotton water and salt stress could be avoided when 66 mm of freshwater was used at the seedling stage when the soil salinity threshold Ce1 was 2.58 g/L, and 412.9 mm of brackish water was used during the other growth stages when Ce2 was 6.62 g/L. Irrigation intervals of 3 days during the flowering and boll-setting stages and 6 days during the other growth stages were recommended. Compared with earlier published results, 1190 m3/ha of surface water and 495 m3/ha of groundwater could be saved in Xinjiang when the above-recommended irrigation strategy is used. Finally, HYDRUS-3D is a valuable and efficient tool for evaluating farmland water and salinity management.