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

Abstract

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 31P 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.