Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: November 7, 2006
Publication Date: July 10, 2008
Citation: Dao, T.H. 2008. Determining Bioactive Phosphorus Fractions in Animal Manure, Soil, and Extracts of Soils and Manures. pp. 86-93. In: Kovar, J. and Pierzinski, G. (eds). Methods of P Analysis for Soils, Sediments, Residuals, and Waters. Rev. Edition. Southern Region SERA-IEG 17. Southern Coop Series Bull. Interpretive Summary: Animal manures are major sources of organic phosphorus applied to soils and are attracting a great deal of research and regulatory interest because animal digestive systems are very inefficient in absorbing and retaining phosphorus, and much of the salts of phytic acid form (phytate) is found intact in animal manure. In spite of the voluminous literature and the number of detailed reports on composition of inorganic phosphorus in manure and in soils, the transformations and fate of organic phosphates is not well understood. In this article, we describe a ligand-based mild fractionation assay that was developed in BARC-EMBUL to differentiate bioactive orthophosphate and organic phosphates, including phytate in manure and soils into pools that reflect their potential for being released to the liquid phase. The task is critical to the accurate assessment of fate of environmental phosphorus and the protracted impairment of water resources by the solubilization and slow release of organic phosphates by phosphorus-releasing enzymes that exist naturally in agricultural soils and natural environments.
Technical Abstract: Enzymatic dephosphorylation of compounds such as inositol phosphates and other orthophosphate monoesters, phosphorylated lipids, and phosphodiesters have been used in their characterization in many biological media including organic residuals and soils. In an enzymatic assay, a manure sample, a soil sample, or an aqueous extract of these matrices is incubated with a specific phosphohydrolase enzyme. The appearance and accumulation of orthophosphate in the reaction medium indicates the presence of a form or class of organic phosphorus-containing compound and concentration of the sample. However, current enzymatic methods have been hampered by the low recovery of organic phosphorus substrates to be a quantitative analytical tool. A ligand-based mild fractionation assay was developed at BARC-EMBUL to differentiate in situ bioactive orthophosphate and orthophosphate monoesters, including inositol phosphates in manure and soils into pools that reflect their potential for being desorbed and released to the liquid phase. The task is critical to the accurate assessment of fate of environmental phosphorus and the protracted impairment of aquatic environments by time-dependent solubilization and dephosphorylation of organic phosphates by ubiquitous phosphohydrolases in agricultural and natural ecosystems.