Application of desulfurized gypsum combined with pig manure to improve soil quality and promote crop growth in saline-alkali soils

Soil salinization is one of the main obstacle restricting agricultural development. Over the past few decades, people have been committed to finding effective improvement practices, but with little success. This study aimed to evaluate the synergistic effects of flue gas desulfurization gypsum (FGD gypsum) and pig manure (PM) on improving saline-alkali soil quality and crop growth in northwest China, focusing on soil alkalinity reduction, nutrient enhancement, and yield promotion across sorghum, millet, and soybean. A field experiment in Yulin City, Shaanxi Province, tested six treatments (amended vs. unamended groups for three crops) with FGD gypsum (24 t ha−1) and PM (24 t ha−1). Soil chemical (pH, ions, nutrients), physical (bulk density, porosity, aggregates), microbial properties, and crop growth were analyzed. Heavy metal risks were assessed against national standards. Amendments significantly reduced soil pH (from 8.68 to 7.65), Na+, Cl−, and HCO3−, while increasing Ca2+, Mg2+, available phosphorus (15.98 to 26.71 mg kg−1), and organic matter (from 17.96 to 22.43 g kg−1). Soil porosity and aggregate stability improved, enhancing microbial biomass. Sorghum exhibited the highest biomass (+56%) and yield (+10.6%) gains. Heavy metal levels remained below safety thresholds, confirming environmental safety. As a result, the soil quality of saline alkali soil has been improved. Combined FGD gypsum and PM effectively remediated saline-alkali soils by mitigating alkalinity, optimizing nutrients, and improving structure, with sorghum being the most responsive crop. This approach offers a low-risk strategy for reclaiming degraded agricultural lands in arid regions.