Tuesday, November 14, 2006 - 8:30 AM

A Methodology to Account for Phosphorus Release Potential from Different Sources of P.

Olawale O. Oladeji1, George A. O'Connor1, Herschel Elliott2, and Jerry B. Sartain1. (1) Univ of Florida, 106 Newell Hall, Gainesville, FL 32611, (2) Penn State Univ, 220 Ag Eng Bldg, University Park, PA 16802-1909

Solubility and P release of P sources depend on source physical and chemical properties. Indices based on limited chemical compositions of the P sources such as phosphorus saturation index [POX/(AlOX+FeOX)] may not adequately predict P release potentials of the wide range of land applied amendments. We investigated impacts of P sources on P losses, and identified a laboratory method that could account for varying P solubility and losses. Four P sources; poultry manure, Boca Raton biosolids (high water soluble P), Pompano biosolids (moderate water soluble P) and TSP were surface applied to a Florida sand at two rates (56kg P ha-1, and 224kg P ha-1) to represent low and high soil P loads typical of P-based and N-based rates. Simulated rainfall was applied to collect runoff and leachates.  Masses of bioavailable P (BAP) lost from various P sources followed similar trends with source percentage water extractable P (PWEP) values, but not with water extractable P (WEP) values (values in parentheses are PWEP, and WEP respectively): TSP (84%; 179g kg-1) > manure (18%; 4.57g kg-1) > Boca Raton biosolids (12%; 5.52g kg-1) > Pompano biosolids (4%; 1.16g kg-1). The BAP losses also have a better relationship with application rate when normalized with PWEP (r2 = 0.81) than with P source coefficient (PSC; calculated as 0.109*WEP0.99) suggested to account for P source solubility (r2 = 0.77). Use of PWEP rather than PSC is suggested as a better method to compare solubility and P release of varying P sources in soils where leachate P loss is significant.