Combined application of a straw layer and flue gas desulphurization gypsum to reduce soil salinity and alkalinity

Burying a straw layer and applying flue gas desulphurization (FGD) gypsum are effective practices to ameliorate soil salinization or alkalization and to increase crop yield; however, little information exists on the effects of such integration in saline-alkali soils. A soil column experiment was conducted to investigate the effects of a straw layer plus FGD gypsum on soil salinity and alkalinity. We placed a straw layer (5 cm thick) at a depth of 30 cm and mixed FGD gypsum into the 0-20 cm soil layer at application rates of 7.5, 15.0, 22.5, and 30.0 t ha^-1, with no straw layer and FGD gypsum as a control (CK). The soil water content in the 0-30 cm soil layer was significantly higher (> 7.8%) in the treated soil profiles after infiltration than in the CK, but decreased after evaporation. The electrical conductivity (EC) of the 10-30 cm soil layer was 230.2% and 104.9% higher in the treated soil profiles than in the CK after infiltration and evaporation, respectively, and increased with increasing rates of FGD gypsum application, with Ca²⁺ and SO₄^2- being the main dissolved salts. Compared to those in the CK, the concentrations of Na⁺, Cl^-, and HCO₃^- decreased in the treated soil profiles at depths above 55 cm, but the other soluble ions increased, after infiltration. A similar trend occurred after evaporation for all soluble ions except for HCO₃^-. The pH and exchangeable sodium percentage in the treated soil profiles were significantly lower than those in the CK over the entire profile, and decreased with increasing FGD gypsum application rates. Therefore, the incorporation of a straw layer plus FGD gypsum can reduce salinity and alkalinity, but the quantity of FGD gypsum should be controlled in saline-alkali soils.