Short-Term Impacts of FGD Gypsum On Soil Properties.

Waters draining into the Great Lakes often pass over agricultural lands resulting in environmental concerns from phosphorus (P) loading into the Great Lakes. Land application of gypsum has the potential to reduce runoff losses of P in two ways. First, the gypsum can improve soil physical properties that enhance infiltration and thereby reduce runoff volume, and second it can alter soil chemistry to reduce the amount of dissolved reactive P in the soil. Flue gas desulfurization (FGD) gypsum is a coal combustion product that is chemically similar to and more readily available than mined gypsum sources in Wisconsin. Research was conducted on lands draining into Green Bay on Lake Michigan and those draining into Lake Superior to determine if land application of FGD gypsum had a beneficial effect on soil physical and chemical properties. Studies were conducted in 2010 and 2011 on private farms that had been planted to corn grain following common local practices.  Within each field, a randomized complete block was designed with individual treatment plots being 3 m by 7.6 m in size. The FGD gypsum was hand-applied post-planting (without incorporation) at rates of 0 (control), 1120 kg/ha, 2240 kg/ha, and 4480 kg/ha. Short-term effect of FGD gypsum on soil physical properties was determined by quantifying bulk density, penetration resistance, aggregate stability, and infiltration rate approximately 12 weeks after FGD gypsum was applied. Effect of FGD gypsum on dissolved reactive P content was also analyzed in the top five cm of soil four and 12 weeks after application.  The additional of gypsum lowered bulk density at the locations with the greatest clay content.  Those sites also showed a significant effect of FGD gypsum addition increasing infiltration rate.  The other tested sites showed minimal effect of FGD gypsum on physical parameters.  However, the dissolved reactive P concentrations were lowered by the addition of FGD gypsum at most locations regardless of texture.