Tuesday, November 14, 2006 - 8:30 AM
213-1
A Methodology to Account for Phosphorus Release Potential from Different Sources of P.
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.
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