Effect of FGD Gypsum and Farming Methods on Phosphorus Loss from Two Agricultural Soils.

Excessive or improper phosphorus (P) fertilizer use increases the risk of P export to surface water and is a major threat to water quality. Minimizing the water quality threat by reducing P loss from soils is necessary. A completely randomized design experiment, conducted in the greenhouse, assessed the capacity of using different tillage methods, different application rates of flue gas desulfurization (FGD) gypsum, and different applied methods of P fertilizer on decreasing total P (TP) and available P (AP) losses from two soil types. Soils were collected from Wooster (silt loam) and Hoytville (clay loam) in Ohio. Each soil was first treated with P that was either surface applied or mixed into the top 20 cm of soil. The soils were then treated with three rates of FGD gypsum (0, 336 and 3360 kg/ha) and two application methods (FGD gypsum surface-applied or mixed thoroughly with the top 0-20 cm soil layer to simulate no-tillage (NT) and tillage, respectively). Soils were planted with annual ryegrass. After three weeks to establish ryegrass growth, 90-min rainfall events were conducted and runoff and leachate water were collected at the end of the rainfall event every two weeks for 12 weeks, and analyzed for TP and AP. Our results indicate P fertilizer applied on the surface (i.e. NT soil) without gypsum significantly (P < 0.05) increased AP loss in runoff compared to P fertilizer mixed thoroughly throughout the 0-20 cm topsoil layer. In leachate water, AP and TP loss from Wooster soil was reduced when FGD gypsum was applied under NT compared to tillage conditions and for the Hoytville soil, the losses under NT were greater than for tillage. Also, for leachate water, there was no significant difference in AP and TP concentrations between the two rates of FGD gypsum, but there was a difference between plus and minus FGD gypsum application. In runoff water, there was little effect of applying FGD gypsum at reducing the concentrations of AP and TP. Overall, this greenhouse study indicates gypsum is a promising soil amendment to reduce P concentrations in leachate water, but may be less effective in reducing P concentrations in runoff water.