Monday, November 5, 2007 - 1:45 PM
121-3

Reducing Off-Site Phosphorus Loss from a Florida Spodosol Amended with Different Phosphorus Sources.

Sampson Agyin-Birikorang, Soil and Water Science Department, University of Florida, 106 Newell Hall, Gainesville, FL 32611, George O'Connor, PO Box 110510, University of Florida, University of Florida, Soil & Water Science Dept., Gainesville, FL 32611-0510, and Olawale Oladeji, Michigan State University, Crop and Soil Science Department,, 512 Plant and Soil Science Building, MSU, East Lansing, MI 48824.

Off-site phosphorus (P) losses from agricultural areas in Florida contribute to groundwater degradation. Drinking-water treatment residuals (WTR) can reduce P leaching , but most studies of WTR effects on soil solution P in Florida soils have been either laboratory incubations, column leaching studies, and indoor rainfall simulation studies that may not be representative of actual field and landscape conditions. We investigated the effects of surface co-applied P sources and an aluminum-based WTR (Al-WTR) on leachate P and Al concentrations in a typical Florida Spodosol under field conditions for 18 mo. Four P sources: poultry manure, Boca Raton biosolids (high water soluble P), Pompano biosolids (moderate water soluble P) and triple super phosphate (TSP), were surface applied to an Immokalee fine sand at P-based (39.6 kg P ha-1) and N-based (179 kg N ha-1) rates, with and without WTR amendment (22 and 0 kg ha-1, respectively). Surface-applied WTR reduced orthophosphate (PO4-P) concentrations in groundwater samples obtained above the spodic horizon at a depth of 0.9 m below the soil surface. Groundwater PO4-P concentrations of the treatments having P-sources applied at the N-based rates were reduced to values below those of the corresponding plots without WTR amendment (from ~ 3.5 mg L-1 to 1.0 mg L-1), and were similar to values of the control plots (0.9 mg L-1). Minimal or no increases in PO4-P concentrations were observed in the groundwater samples of the treatments with the P-sources applied at P-based rates, with or without WTR amendment. The increase in Al concentrations of surface soils following surface WTR application (from ~5 mmol Al kg-1 to ~32 mmol Al kg-1) were not accompanied by increases in the total dissolved Al concentrations in groundwater and surface runoff. We conclude that WTR can be safely used to enhance P sorption capacity of Florida sandy soils and to reduce P leaching into the groundwater without increasing the Al concentration in groundwater and surface runoff.

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