Long-term performance of flue gas desulfurization gypsum in a large-scale application in a saline-alkali wasteland in northwest China

Flue gas desulfurization (FGD) gypsum has been used as an amendment to reduce soil salinization and alkalinization worldwide. However, the effective and safe use of FGD gypsum in agricultural land is still debatable in some countries, although many studies have reported its beneficial effects on soil management. Therefore, a study was conducted on wasteland (600 ha) close to the Yellow River in Inner Mongolia, China. The main aim of this research was to evaluate the long-term effects of FGD gypsum application on soil salinity and sodicity, crop production and heavy metals in soils and crops. The results showed that soil pH and exchangeable sodium percentage (ESP) in topsoil (0-20 cm) decreased dramatically during the first year, while a substantial reduction of electrical conductivity (EC) occurred during the second year after FGD gypsum application. Four years later, the EC, pH and ESP levels in reclaimed soils were 58.3%, 92.2% and 95.2% lower, respectively, than those in the initial soils. In addition, the FGD gypsum application altered the major water-soluble ion composition of dissolved salts, showing high Ca2+ and SO42− concentrations and low concentrations of HCO3−, CO32− and other water-soluble ions. After reclamation, the crop yields gradually increased over time, and the sunflower and corn yields reached more than 90% of the levels of local production of these crops. Moreover, the heavy metal (Cd, As, Pb, Hg and Cr) contents of the FGD gypsum-reclaimed soils and crops was far lower than the established standards and below detectable limits. This study provides convincing evidence of the benefits of the large-scale use of FGD gypsum to reclaim saline-alkali soils.