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Influence of Flue Gas Desulfurization Gypsum on Reducing Soluble Phosphorus in Successive Runoff Events from a Coastal Plain Bermudagrass Pasture

Dexter B. Watts, H. Allen Torbert
Journal of environmental quality 2016 v.45 no.3 pp. 1071-1079
Cynodon dactylon, coastal plains, eutrophication, growing season, gypsum, pastures, phosphorus, poultry manure, rainfall simulation, residual effects, runoff, Southeastern United States
Controlling the threat that pastures intensively managed with poultry litter (PL) pose to accelerating eutrophication is a major issue in the southeastern United States. Gypsum (CaSO₄) has been identified as a promising management tool for ameliorating litter P losses to runoff. Thus, research was conducted to elucidate gypsum’s residual effects on P losses from a bermudagrass (Cynodon dactylon L.) pasture. Runoff events (60 min) were created using rainfall simulations. Treatments consisted of applying four flue gas desulfurization (FGD) gypsum rates (0, 2.2, 4.4, and 8.9 Mg ha⁻¹) to bermudagrass fertilized with 13.4 Mg ha⁻¹ PL plus a nonfertilized check (no litter or gypsum) and 8.9 Mg ha⁻¹ FGD gypsum only as controls. Rainfall simulations (∼ 85 mm h⁻¹) were conducted immediately, 5 wk, and 6 mo (i.e., at the end of growing season) after PL application to determine gypsum’s effectiveness at controlling P loss over successive runoff events. The greatest dissolved P (DP) in runoff occurred immediately after PL application. Gypsum effectively reduced cumulative DP concentration losses (54%) compared with PL alone in initial runoff events. Gypsum reduced DP concentrations in succeeding runoff events also regardless of timing, suggesting that its effect is persistent and will not diminish over a growing season. Generally, maximum DP reductions were achieved with 8.9 Mg ha⁻¹. However, it was surmised from this study that optimal P reduction in a bermudagrass pasture can be achieved with 4.4 Mg ha⁻¹. Information ascertained from this study may be useful in aiding land managers making prescriptions for management practices that reduce DP losses from agricultural fields.