Phosphorus Species Composition of Poultry Manure-Amended Soil Using High-Throughput Enzymatic Hydrolysis

Nutrient management planning tools including P indices would have enhanced diagnostic and predictive abilities if forms of organic P transformable to inorganic phosphate by soil microbes (enzyme-labile P) can be assessed. Enzyme-labile P species were tracked in a time series of manure-amended soil samples by modifying an enzymatic P assessment tool first developed by Zhongqi He for manures. By adapting this method to a microplate reader format, up to 96 samples were processed simultaneously. Enzyme measures were compared with those made on the same samples using solution P-31 nuclear magnetic resonance spectroscopy. Enzymatic tracking of P species in manure-amended soil extracts is robust; 25 to 36% of P extracted by NaOH ethylenediaminetetraacetic acid was liberated as orthophosphate after incubating samples with enzymes. These increases in molybdate-reactive P (MRP) due to enzymatic hydrolysis exceeded MRP detected in bicarbonate extracts, suggesting the true bioavailable fraction of soil P is underestimated using traditional, static tools such as Olsen P or Mehlich-3 P. This efficient assessment tool should enhance our ability to assess P classes and enzyme-labile P in manure-amended soil.