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 (Po) are considered bioavailable if they can be hydrolyzed to inorganic P (Pi). Therefore, investigation of the susceptibility of manure Po to hydrolysis may increase our understanding of manure Po 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 Po in animal manure. A scheme of sequential enzymatic release of Po in manure was developed and then used to investigate changes in swine and cattle manure P distribution after storage at −20°C, 4°C or 22°C for about a year. Assuming that the P distribution in manure maintained at −20°C remained unchanged (i.e., similar to fresh manure), bioavailable P (Pi and enzyme-hydrolysable Po) in swine manure remained relatively constant [72.8–76.3% of total P (Pt)]. Soluble but enzymatically unhydrolysable Po (Pue) increased from 7.2% to 32.1% of Pt during storage at 4°C. In cattle manure, bioavailable P decreased from 71.6% to 62.9% of Pt, and Pue increased from 21.7% to 37.2% of Pt during storage at 22°C. These data indicated that the major change during the storage of animal manure for a year was the increase in Pue, 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.