Decreasing Phosphorus Loss in Tile‐Drained Landscapes Using Flue Gas Desulfurization Gypsum

Elevated phosphorus (P) loading from agricultural nonpoint‐source pollution continues to impair inland waterbodies throughout the world. The application of flue gas desulfurization (FGD) gypsum to agricultural fields has been suggested to decrease P loading because of its high calcium content and P sorbing potential. A before–after control–impact paired field experiment was used to examine the water quality effects of successive FGD gypsum applications (2.24 Mg ha −1 ; 1 ton acre −1 each) to an Ohio field with high soil test P levels (>480 ppm Mehlich‐3 P). Analysis of covariance was used to compare event discharge, dissolved reactive P (DRP), and total P (TP) concentrations and loadings in surface runoff and tile discharge between the baseline period (86 precipitation events) and Treatment Period 1 (42 precipitation events) and Treatment Period 2 (84 precipitation events). Results showed that, after the first application of FGD gypsum, event mean DRP and TP concentrations in treatment field tile water were significantly reduced by 21 and 10%, respectively, and DRP concentrations in surface runoff were significantly reduced by 14%; however, no significant reductions were noted in DRP or TP loading. After the second application, DRP and TP loads were significantly reduced in surface runoff (DRP, 41%; TP 40%), tile discharge (DRP, 35%; TP, 15%), and combined (surface + tile) discharge (DRP, 36%; TP, 38%). These findings indicate that surface application of FGD gypsum can be used as a tool to address elevated P concentrations and loadings in drainage waters. Core Ideas A paired field study demonstrated the water quality benefits of FGD gypsum. FGD gypsum improved aggregate stability and increased infiltration. FGD application reduced dissolved and total P concentrations. FGD gypsum reduced dissolved and total P loads. Significant reductions were realized in surface and tile drainage discharge.