Wednesday, November 15, 2006

Fertilizer Value of Phosphorus Extracted From Liquid Swine Wastewater.

Philip Bauer1, Ariel Szogi2, and Matias Vanotti2. (1) USDA-ARS, USDA/ARS Coastal Plains Research Center, 2611 W. Lucas St., Florence, SC 29501-1241, (2) USDA/ARS Coastal Plains Res Cn, 2611 W. Lucas St., 2611 W. Lucas St., Florence, SC 29501-1241, United States of America

A precipitate of calcium phosphate is produced and recovered using a new treatment process developed for removal of P from swine wastewater. We conducted a greenhouse study to evaluate P availability and plant response to the recovered P material. Calcium phosphate precipitate (125 g P/kg) with particle sizes of 0.5-1 mm, precipitate with particles sizes of 2-4 mm diameter, and triple superphosphate (202 g P/kg) were mixed with soil (sandy soil texture, initial P content of 1.7 mg P per kg soil, pH 6.5) at rates of 0, 22, 44, 88, and 176 mg P per kg soil and placed in 15-cm diameter pots. Pots were watered (100 g water per kg soil) and incubated on greenhouse benches for 1 month before planting ryegrass (Lolium multiflorum Lam.) seeds. Plants were harvested by clipping approximately 2.5 cm above the soil surface at 2, 4, and 6 weeks after emergence. Dry weight and P concentration of the ryegrass tissues were measured at each clipping. The recovered P material with 2-4 mm sized particles did not substantially affect biomass or plant P concentration at any rate. Biomass increased with increasing P rate up to 44 g/kg for both the recovered P materials with 0.5-1 mm sized particles and for triple superphoshate, while tissue P concentration continued increasing up to 176 mg/kg for these two materials. Total P removal per pot by plants fertilized with 22 mg/kg of the 0.5-1 mm particle size was about 20% of that by plants fertilized with triple superphosphate at the rate. At the 44, 88, and 176 mg P/kg rates, P removal by plants for this treatment was about 60% of those fertilized with triple superphosphate. This initial study suggests this precipitate material may be an effective slow-release P fertilizer for plant production.