Managing Surface Water Inputs to Reduce Phosphorus Loss from Cranberry Farms.

Cranberries are the largest cash crop in Massachusetts, accounting for one-fourth of U.S. cranberry supply, but water quality concerns, water use, and wetland protection laws challenge their production. Pond water used for harvest and winter flooding accounts for up to two-thirds of phosphorus (P) losses in drainage waters. Consequently, use of P sorbing salts to treat pond water holds promise in the mitigation of P losses from cranberry farms. Laboratory evaluation of aluminum (Al), iron (Fe), and calcium (Ca) based salts was conducted to determine the application rate required for reducing P in shallow and deep water ponds used for cranberry production. Limited P removal (<22%) with calcite and gypsum was consistent with their relatively low solubility. Slaked lime reduced total P up to 66%, but caused pH increases (> 8) that were likely to be detrimental to cranberry production. Ferric sulfate and alum applications of 15 mg L^-1 resulted in near-complete removal of total P, which decreased from 102 to <10 μg P L^-1. However, ferric sulfate application lowered pH below the recommend range for cranberry soils. Field testing of alum demonstrated that at a dose of 15 mg L-1 (~1.4 Al mg L^-1), total P in pond water was reduced by 78-93%. Laboratory and field experiments support the recommendation of occasional alum application as a cost-effective remedial strategy for reducing P in surface water used for cranberry production.