Enzymatic hydrolysis of organic phosphorus in extracts and resuspensions of swine manure and cattle manure

Animal manure can be a valuable resource of P for plant growth. Organic phosphates (P-o) are considered bioavailable if they can be hydrolyzed to inorganic P (P-i). Therefore, investigation of the susceptibility of manure P-o to hydrolysis may increase our understanding of manure P-o bioavailability. In this study, we demonstrate that three orthophosphate-releasing enzymes, acid phosphatase from wheat germ, alkaline phosphatase from bovine intestinal mucosa, and fungal phytase from Aspergillus ficcum, were able to hydrolyze certain amounts of P-o in animal manure. A scheme of sequential enzymatic release of P-o in manure was developed and then used to investigate changes in swine and cattle manure P distribution after storage at -20degreesC, 4degreesC or 22degreesC for about a year. Assuming that the P distribution in manure maintained at -20degreesC remained unchanged (i.e., similar to fresh manure), bioavailable P (P-i and enzyme-hydrolysable P-o) in swine manure remained relatively constant [72.8-76.3% of total P (P-t)]. Soluble but enzymatically unhydrolysable P-o (P-ue) increased from 7.2% to 32.1% of Pt during storage at 4degreesC. In cattle manure, bioavailable P decreased from 71.6% to 62.9% of P-t, and P-ue increased from 21.7% to 37.2% of P-t during storage at 22degreesC. These data indicated that the major change during the storage of animal manure for a year was the increase in P-ue, so manure P solubility may increase with storage, but the increase would not produce more bioavailable P in the manure. The effects of storage on the bioavailability of manure P should be further investigated to develop an efficient manure-P management strategy.