FGD gypsum use as a soil amendment to reduce soluble P in soil

Authors: Watts, Dexter; Torbert, Henry - Allen

Submitted to: Southern Conservation Agricultural Systems Conference
Publication Type: Proceedings
Publication Acceptance Date: 7/20/2010
Publication Date: 7/20/2010
Citation: Watts, D.B., Torbert III, H.A. 2010. FGD gypsum use as a soil amendment to reduce soluble P in soil. Southern Conservation Agricultural Systems Conference. In: Conservation Agriculture Impacts-Local and Global, Proceedings of the 32nd Southern Conservation Agricultural Systems Conference, July 20-22, 2010, Jackson, Tennessee. p.89-96.

Interpretive Summary: Phosphorus from manure can potentially cause a negative impact on water quality. Use of gypsum with manure may reduce manure P loss in surface water runoff. A study was performed to evaluate the use of commercial gypsum and power company gypsum as a management practice to reduce P loss in a permanent bermudagrass pasture. The application of gypsum to the soil improved P retention. Greater P retention in soil suggests that less P was loss with surface water runoff. Also, the power company gypsum was just as effective as the use of commercial gypsum. Thus, this study shows that gypsum can be used to reduce the loss of P from agricultural fields.

Technical Abstract: Phosphorus loss from land-applied manure can be a major threat to water quality. Use of gypsum as a soil amendment could potentially minimize the water quality threat by reducing P loss from manured soils. Thus, a field study was conducted to evaluate if gypsum and lime amendment would reduce the extractability of P in soil. The study was located at the Sand Mountain Substation in the Appalachian Plateau region of Northeast Alabama, USA, on a Hartselle fine sandy loam (fine-loamy, siliceous, subactive, thermic Typic Hapludults). Poultry litter was applied at a rate of 4 tons acre-1in an established bermudagrass pasture (Cynodon dactylon L.). Treatments consisted of commercial gypsum (1, 5, and 10 tons acre-1), flue-gas desulfurization (FGD) gypsum (1, 5, and 10 tons acre-1), FGD gypsum + fly ash (1, 5, and 10 tons acre-1), lime (5 tons acre-1), gypsum + lime (5 ton acre-1 gypsum and lime at an equivalent Ca content), and a control. Soil samples were collected at two depths (0-2 and 2-6 inches) and evaluated for water extractable P, Mehlich 3 extractable P, and Total P concentrations. Phosphorus concentrations in soil were the greatest in the first soil samples collected after poultry litter application. Also the greatest concentration of P was observed in the surface 0-2 inches of soil. Overall, the addition of all of the gypsum and lime treatments significantly reduced water extractable P concentrations in soil. No significant differences were observed between gypsum sources at the same rate. Averaged across gypsum sources (commercial gypsum, FGD gypsum, and FGD gypsum + fly ash), increases in application rates resulted in a greater reduction of soluble P. Similar results were achieved at the lower depths. No significant differences between treatments were observed for the Mehlich 3 P and total P concentrations. However, a trend was observed with the use of Mehlich 3. The Mehlich 3 extraction solution resulted in an increased P concentration with the gypsum sources and lime treatment additions. Information from this study may be useful in helping land managers and producers reduce the potential loss of P from agricultural fields.