Potential of Flue-Gas Desulfurization (FGD) Gypsum for Reducing Soil Phosphorus Losses in the Great Lakes Region.

Phosphorus in runoff from soils can significantly impact surface water quality. The application of flue-gas desulfurization gypsum (FGDG) has been shown to reduce P losses from agricultural soils in previous studies, but this effect has not been widely studied in the Midwest. The aim of this study was to compare Bray P and water-extractable P (WEP) concentrations after FGDG application for three loamy field sites in southeastern Wisconsin. The Bray P soil test was selected because it is the standard soil P test in Wisconsin, and WEP has been shown to strongly correlate to the dissolved P exported during a runoff event. The treated soil received an FGDG application of 2.24 mt ha^-1 in the spring of 2014 and fall of 2015. Soil samples were collected to a 15 cm depth prior to FGDG application, and in the spring of 2015 after treatment. A strong correlation between the soil Bray P and WEP was observed for both the control and treated soils. The linear regression models resulted in an R² value of 0.815 for the treated samples and 0.873 for the untreated samples. Comparison of the treated and control models (Bray P vs. WEP) revealed that there was a significant difference in the intercepts, but not the slopes of the two models. The equal slopes reveal that the FGDG did not have a significant effect on the positive linear relationship of the Bray P to WEP of the soil. However, the significant difference between intercepts indicates that for a given Bray P value, the WEP for the treated soil is significantly lower than that of the untreated soil. The results of this study indicate that FGDG may be an effective method of reducing P losses on Wisconsin soils.