Laboratory Procedures for Characterizing Manure Phosphorus

Abstract Phosphorus runoff from agricultural land contributes to accelerated eutrophication of surface waters. In areas with intensive animal farming, P loss from 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 (H 2 O), 0.5 M NaHCO 3 , 0.1 M NaOH, 1.0 M HCl, and 5% trichloroacetic acid (TCA). Two extraction procedures were tested: (i) independent, with dried, ground samples being extracted repeatedly and P measured for each extractant; and (ii) sequential, with each sample being repeatedly extracted by H 2 O, NaHCO 3 , NaOH, and HCl, in that order. For the independent procedure, H 2 O extracted 53 to 64%, NaHCO 3 64 to 72%, NaOH 33 to 54%, HCl 90 to 97%, and TCA 84 to 96% of the total P in manure. Sequentially, H 2 O, NaHCO 3 , NaOH, and HCl extracted 70, 14, 6, and 5% of the total P in the dairy, and 49, 19, 5, and 25% of the total P in the poultry sample, respectively. Manure P release was not greatly affected by shaking time but decreased rapidly with increasing number of repeated extractions. A large portion of P in manure being extractable by H 2 O or NaHCO 3 suggests weak binding energy of P and hence a high susceptibility for loss to waters when conditions favor runoff. A 1‐h shaking of manure with H 2 O may provide a quick measure of the relative magnitude of P that is most susceptible. Further investigation relating manure P fractions with P in runoff would help identify management alternatives for reduced P losses.