EVALUATION OF ORGANIC PHOSPHORUS m ANIMAL MANURE BY ORTHO-PHOSPHATE RELEASING ENZYMATIC HYDROLYSIS

摘要

The chemical composition of phosphorus in manure significantly impacts its transport and potential bioavailability. As much as 50% of the phosphorus in animal manure is present in organic forms (P_o). Therefore, characterization of P_o and its bioavailability may contribute to effective manure P management. Phosphatases catalyze reactions that release orthophosphate (P_i) from various types of organic phosphorus compounds. The possibility of using those enzymes for classifying manure hydrolysable P_oand for evaluating P_obioavailability was explored. Swine manure and cattle manure were first sequentially fractionated into water-soluble, NaHCO_3-soluble, and NaOH-soluble P. Fractions were then incubated with phytase, acid phosphatase, alkaline phosphatase, nuclease P1, nucleotide pyrophosphatase, or their combinations. The released P_i was determined by a molybdate blue method. The difference in P_I determined after incubation in the presence and absence of an enzyme reflected the corresponding type and amount of P_o in the sample. Based on this research, we selectively applied acid phosphatase from potato, acid phosphatases from potato and wheat germ, and both phosphatases plus nuclease P1 to identify and quantify simple monoester P, phytate (inositol hexaphosphate)-Iike P, and DNA-like P, respectively. "With this approach, we examined the distribution of the three types of P_o in 11 dairy manures. Phytate-like P was present as the major hydrolysable P_o in all three fractions. Its concentrationin the H_2O fraction was positively related to total manure P. However, the concentration in the NaHCO_3 and NaOH fractions was more correlated, respectively, to the NaHCO_3 - or NaOH-extracted P_o. We also investigated the change in manure P distribution after 1 yr storage at 4°C (swine manure) and 20°C (cattle manure) using enzymatic hydrolysis. Our data indicate that the amounts of bioavailable P (P_i and enzyme hydrolysable P_o) in these manures remained relatively constant during storage. Soluble but enzymatically unhydrolysable P_o, however, increased significantly. Our study demonstrates that enzymatic hydrolysis is an effective approach to identify and quantify hydrolysable P_o in animal manure.