Laboratory procedures for characterizing manure phosphorus

Phosphorus runoff from agricultural land contributes to accelerated eutroph ication of surface waters. In areas with intensive animal farming, P loss f rom manured fields may be elevated due to high concentrations of soluble P in manure. We characterized P in dairy and poultry manure for the relative dissolution and fraction distribution using deionized water (H2O), 0.5 M Na HCO3, 0.1 M NaOH, 1.0 M HCl, and 5% trichloroacetic acid (TCA). Two extract ion procedures were tested: (i) independent, with dried, ground samples bei ng extracted repeatedly and P measured for each extractant; and (ii) sequen tial, with each sample being repeatedly extracted by H2O, NaHCO3, NaOH, and HCl, in that order. For the independent procedure, H2O extracted 53 to 64% , NaHCO3 64 to 72%, NaOH 33 to 54%, HCl 90 to 97%, and TCA 84 to 96% of the total P in manure. Sequentially, H2O, NaHCO3, NaOH, and HCl extracted 70, 14, 6, and 5% of the total P in the dairy, and 49, 19, 5, and 25% of the to tal P in the poultry sample, respectively. Manure P release was not greatly affected by shaking time but decreased rapidly with increasing number of r epeated extractions. A large portion of P in manure being extractable by H2 O or NaHCO3 suggests weak binding energy of P and hence a high susceptibili ty for loss to waters when conditions favor runoff. A l-h shaking of manure with H2O may provide a quick measure of the relative magnitude of P that i s most susceptible. Further investigation relating manure P fractions with P in runoff would help identify management alternatives for reduced P losse s.