Reducing Water-Soluble Phosphorus in Soil through Flue Gas Desulfurization Gypsum Application: Year of Application...

Phosphorus runoff from agricultural land to surface water bodies, such as the Great Lakes, is an important environmental concern. Soil amendments, such as gypsum, may alter the chemistry of the soil solution to reduce the amount of water-soluble P (WSP) available for loss to runoff, and as such, the NRCS now recommends gypsum application as a Conservation Practice Standard (Code 333) for improving water quality. Interest in gypsum use has also increased as availability has increased from production of flue gas desulfurization (FGD) gypsum at many coal-burning power plants throughout the United States. This study tested three rates of unincorporated, surface-broadcast FGD gypsum application at 23 field sites in Wisconsin. The optimal rate for reducing WSP concentration and the relationship between selected soil properties and the beneficial effect of FGD gypsum application were evaluated. The FGD gypsum reduced WSP ( < 0.0001), with a significant effect compared with the control at the lowest tested rate of 1120 kg ha at 5 of the 23 sites. Few other sites saw a significant benefit. Correlation indicated that sites showing a beneficial reduction of WSP from FGD gypsum application were those with greater soil test P ( = 0.0002) and lower cation exchange capacity ( = 0.0087) values.