Modeling response of spring wheat yield to soil water and salt contents and its application in scheduling brackish water irrigation

Abstract

Fresh water shortage and soil salinization are two key factors restricting agricultural development in arid areas. Brackish water is a possible alternative resource for crop irrigation, but brackish water irrigation should be properly scheduled to balance crop yield increment and soil salinization control. To determine suitable water amounts for crop irrigation under different water salinities, an agro-hydrological model, LAWSTAC, was used to simulate soil water and salt dynamics and crop growth in salinized croplands in an arid region of Northwest China. Model calibration and validation results of soil water content, salt concentration, groundwater table depth, leaf area index, biomass, and crop yield agreed well with the field measurements of spring wheat (Triticum aestivum L.) under both fresh and brackish water irrigations with the Nash and Sutcliffe efficiency of 0.50–0.96 and the coefficient of determination of 0.55–0.98. The model was further used to simulate crop yields for 432 combinations of six irrigation levels, six irrigation water salinity levels, four initial groundwater table depths, and three initial soil salt concentrations. Based on the simulation results, a function of relative crop yield response to soil water content and salt concentration was developed, which is expressed as the product of a hyperbolic function for water stress and a sigmoid function for salt stress. For known initial soil water content and salt concentration, a procedure was proposed to determine suitable water amounts applied to the cropland under different irrigation water salinities for expected crop yields using the developed crop-water-salinity production function. With the procedure, the minimum amount of applied water with known salinity can be obtained for an expected relative crop yield. The results are helpful to the amount control in fresh or brackish water irrigations for sustainable crop production in salinized croplands.