Phosphorus Solubility and Functional Groups in Dairy Feces from Two Farms.

The forms of P were examined in fecal samples from two dairy farms. Farm A samples averaged 11,302 mg/kg as total P and 3,979 mg/kg as water extract P, compared to 4,173 mg/kg and 1,456 mg/kg for Farm B samples.  P speciation was determined in extracts of water, 0.025 M NaOH with 50 mM EDTA (NaOH), or 100 mM Na acetate, pH 5.0 plus 20 mg Na dithionite/ml (NaAc) using ³¹P-NMR.  Water extracted 35% of total P whereas NaOH and NaAc extracted >80% of total P.  The ³¹P-NMR results suggest that in general water is not an effective extractant as several important P forms (phosphonate, IHP, pyrophosphate, and polyphosphate) were not detected in the extracts but their existence were confirmed in NaOH and NaAc extracts.  However, water extracts had greater amounts of DNA and other diester P than the other two solutions.  This suggests that degradation might have occurred in the alkaline- or acid- based solutions. Regardless of type of extractant, the vast majority of total P in dairy feces existed as orthophosphate. Furthermore, orthophosphate accounted for a higher proportion of total P in the sample from Farm A (82 and 85%) than Farm B (64 and 72%).