COMPARATIVE EVALUATION OF WATER EXTRACTABLE PHOSPHORUS IN BIOSOLIDS AND LIVESTOCK MANURES

Phosphorus (P)-based nutrient management will inevitably be required for land application of biosolids and manures. The water extractable portion of P has been used recently to estimate the potential for land-applied manures to enrich P in leachate and runoff. We compared the water extractable P (H2O-P) of biosolids with manures and inorganic fertilizers. Forty-two biosolids (representing a variety of wastewater and biosolids treatment processes), 13 manures and manure composts from different livestock, and 2 fertilizers samples were evaluated. The mean percent water extractable P (WEP = [H2O-P ÷ PT]× 100) for all biosolids was significantly lower than for all manures and fertilizers tested. This difference was primarily attributable to the higher levels in biosolids of Al and Fe that tend to fix P in water-insoluble forms. Among the biosolids tested, those from facilities that employ biological P removal had the highest average WEP. As states begin to require P-based management, it is important that policies reflect the substantially different potential for soluble P losses in runoff and drainage among biosolids, livestock manures and commercial fertilizers.