ObjectiveIn order to comprehensively study the effect of desulfurized gypsum in improving saline-alkali soils, this paper statistically analyzed the change characteristics of soil pH value, exchangeable sodium percentage (ESP), soil electrical conductivity (EC), and crop yield after applying 0~60 t·hm^-2 desulfurized gypsum in the northwest, north, northeast, and coastal areas of China through literature search. To achieve this, a comprehensive improvement evaluation model of saline-alkali soil was used in which the desulfurized gypsum amount was designed as an independent variable based on the grey relational analysis and entropy weight method.MethodSoil pH value and ESP are often used to evaluate the alkalization property of saline-alkali soil while EC is used to evaluate the salinization property of saline-alkali soil. This paper used the data of literature to explore the relative change rates of soil pH, ESP, and EC in 0~20 cm soil layer with and without desulfurized gypsum within 1 year after the crop harvest in order to quantitatively reveal its improvement effect. Grey relational analysis and entropy weight method were used to synthesize three soil indexes to evaluate the improvement effect of desulfurized gypsum on saline-alkali soil. Due to the few literature data on light saline-alkali soil and moderate saline-alkali soil, the application of desulphurized gypsum in severe saline-alkali soil was mostly studied. This paper combined light saline-alkali soil and moderate saline-alkali soil into light and moderate saline-alkali soil for analysis.ResultApplication of desulfurized gypsum reduced soil pH and ESP and increased crop yield, but increased EC. As the application rate of desulfurized gypsum increased, the decrease rate of pH and ESP and the increase rate of crop yield increased first and then decreased whereas the increase rate of EC showed an increasing trend. When the amount of desulfurized gypsum applied to moderate saline-alkali soil and severe saline-alkali soil exceeded 30 t·hm^-2, the increase rate of crop yield(Oil sunflower, alfalfa, corn, rice, wheat, Lycium barbarum, and sweet sorghum) showed a decreasing trend. To further analyze the effect of desulfurized gypsum on the improved saline-alkali soil, an entropy weight grey correlation evaluation model was established, and the application of desulfurized gypsum was optimized.ConclusionThrough the study on the improvement effect of desulfurized gypsum applied in the range of 0~60 t·hm^-2 in saline-alkali soil, using statistical analysis and mathematical modeling, it was concluded that the amount of 18~22 t·hm^-2 desulfurized gypsum in light and moderate saline-alkali soil; the amount of 23~29 t·hm^-2 desulfurized gypsum in severe saline-alkali soil could achieve good soil improvement effect and increase crop yield. The research results provide a reference for improving saline-alkali soil with desulfurized gypsum.