PHOSPHORUS DISTRIBUTION IN DAIRY MANURES

Authors: He, Zhongqi; Griffin, Timothy; Honeycutt, Charles

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2003
Publication Date: 7/15/2004
Citation: He, Z., Griffin, T.S., Honeycutt, C.W. 2004. Phosphorus distribution in dairy manures. Journal of Environmental Quality. 33:1528-1534

Interpretive Summary: Phosphorus (P) exists in animal manure in various forms. In this study, we investigated the distribution of P forms in 13 dairy manures obtained from different sources and their relationships with total manure P. Although the amounts of various P forms were different in these manures, relationships of some P forms with total manure P were observed. For instance, water-extractable inorganic P, the major inorganic P component, and phytate-like P, the major enzymatic hydrolysable organic P, were both positively correlated to total manure P. Findings in this study could enhance our understanding of manure P chemistry, providing insight into improving management of manure P.

Technical Abstract: The chemical composition of manure P is a key factor determining its potential bioavailability and susceptibility to runoff. The distribution of P forms in 13 dairy manures was investigated with sequential fractionation coupled with orthophosphate-releasing enzymatic hydrolysis. A large portion of manure P was H2O extractable, varying from 1,400 to 6,810 mg inorganic P (Pi) kg-1 DM and 130 to 1,660 mg organic P (Po) kg-1 DM. In the NaHCO3 fraction, Pi varied between 740 and 4,200 mg P kg-1 DM, and Po varied between 340 and 1,550 mg P kg-1 DM. In the NaOH fraction, Pi fluctuated around 200 mg P kg-1 DM, and Po ranged from 130 to 630 mg P kg-1 DM. Phytate-like P was present as the major hydrolysable Po in all three fractions (26 to 605 mg kg-1 DM). Although the concentrations of P species varied significantly in these manures, correlations among some P forms with total manure P were observed. For example, H2O-extracted Pi was correlated with total manure P (r =0.79), and NaOH-extracted Po was correlated to total manure P (r =0.91). We also demonstrated that P released by a single extraction with sodium acetate (100 mM, pH 5.0) was equal to the summed amount of H2O-, NaHCO3-, and NaOH-extractable P fractionated sequentially. Thus a single extraction by sodium acetate buffer could provide an efficient evaluation of plant available P in animal manure, while the sequential fractionation approach provides more detailed characterization of manure P.