Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: UNDERSTANDING PHOSPHORUS CHEMISTRY IN MANURE AND SOIL AND THEIR INTERACTIONS TO TREAT AND CONTROL PHOSPHORUS MOVEMENT IN THE ENVIRONMENT Title: Ligand Effects on Phytic Acid in Animal Manures: Assessing Time Dependence of Inositol Phosphate Solubilization and Bioactivity

Author
item Dao, Thanh

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: May 25, 2006
Publication Date: October 31, 2006
Citation: Dao, T.H. 2006. Ligand effects on phytic acid in animal manures: assessing time dependence of inositol phosphate solubilization and bioactivity. In: Turner, B.L., Richardson, A.E., Mullaney, E.J., editors. Inositol Phosphates: Linking Agriculture and Environment. CAB International, Oxfordshire, UK. p. 169-185.

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 of animal digestive systems are very inefficient in absorbing or retaining phosphorus, and much of the phytic acid form of feed phosphorus (inositol hexaphosphate) 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 tranformations and fate of organic phosphates is not well understood. In this article, the factors that affect the processes of solubilization and degradation of soluble and insoluble orthophosphate and phytate are examined to propose mechanisms by which these phosphorus fractions are solubilized and hydrolyzed to replenish the water-soluble phosphorus fraction. A mild in situ ligand-based enzymatic assay developed in this laboratory to obtain insights about how stable organic phosphates are to chemical and enzymatic degradation and solubilization in animal manure is described. In a medium that is rich in carbon material such as manure and manure-amended soils, and the ubiquitous presence of phytate-degrading and phosphorus-releasing enzymes in the soil and environment, biological and biochemical mechanisms more adequately reflect the availability of manure phosphorus to microorganisms and plants over time. Moreover, these mechanisms can reveal the underlying potential for the slow-release release of soluble phosphorus and the protracted impairment of aquatic environments by agricultural phosphorus.

Technical Abstract: Animal manures are major sources of organic phosphorus applied to soils and are attracting a great deal of research and regulatory interest because of the inefficiency of animal digestive systems in absorbing or retaining phosphorus, and much myo-inositol-1, 2, 3, 5/4, 6 hexakis dihydrogenphosphate or phytic acid (inositol hexaphosphate) is found intact in animal excreta. In spite of the voluminous literature and the number of detailed reports on composition of inorganic phosphorus in manure and soil, speciation and fate of organic inositol hexaphosphate and other inositol phosphates is yet not well understood. In this chapter, the factors that affect the processes of solubilization and dephosphorylation of dissolved and insoluble complexed orthophosphate and inositol hexaphosphate are examined to propose mechanisms by which these phosphorus fractions are solubilized and hydrolyzed to replenish the water-soluble phosphorus fraction. A mild in situ ligand-based enzymatic assay used to obtain insights about the biological stability of inositol phosphates in animal manure is described. In carbon-rich media such as manure and manure-amended soils, and the ubiquitous presence of extracellular phosphohydrolases, biological and biochemical mechanisms more adequately reflect the availability of manure phosphorus pools to microorganisms and plants over time. Moreover, these mechanisms can reveal the underlying potential for the timed release of bioactive phosphorus and protracted impairment of aquatic ecosystems by agricultural phosphorus.

Last Modified: 10/23/2014
Footer Content Back to Top of Page