Submitted to: Environmental Remediation Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/25/2005
Publication Date: 12/25/2005
Citation: Dao, T.H. 2005. Differentiating forms and potential bioactivity of environmental phosphorus. In: Proceedings of the Environmental Remediation Approaches to Municipal and Industrial Pollution in Vietnam Conference, October 25-26, 2005, Ho Chi Minh City, Vietnam. p. 148-156. Interpretive Summary: Organic phosphorus is added to soils when animal manure and crop residues are returned and incorporated in soil. There is a great deal of research and regulatory interest because livestock and poultry are very inefficient in retaining dietary phosphorus, and much of the phytic acid form of feed phosphorus is excreted in animal manure. Although there are many detailed reports on composition of inorganic phosphorus in manure and in soils, the transformations and fate of organic phosphates is not well understood. Factors affecting the solubilization of phytate are examined to propose mechanisms by which these phosphorus fractions are solubilized and hydrolyzed to replenish the water-soluble phosphorus fraction. This work led to the development of a mild in situ ligand-based enzymatic assay in this laboratory to quantify how stable organic phosphates are to chemical and enzymatic degradation and solubilization in animal manure. 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, it is concluded that biological and biochemical mechanisms are more adequate in describing the availability of manure phosphorus to microorganisms and plants over time. In addition, these biochemical processes reveal the underlying potential for the slow-release of soluble phosphorus and the protracted impairment of water quality by agricultural phosphorus.
Technical Abstract: Animal manures and organic sources of nutrients such as crop residues are major sources of organic phosphorus (P) applied to soils. They are attracting a great deal of research attention and regulatory interest because animal digestive systems are markedly inefficient at retaining dietary phosphorus, and much of the feed phosphorus that occurs as myo-inositol hexakis dihydrogenphosphate or phytic acid is found intact in the animal feces. As manure organic P is environmentally bioactive, a novel in situ enzyme hydrolysis assay was developed to identify water soluble- and labile complexed P pools, and to determine mechanisms controlling P solubilization and hydrolysis to replenish the environmentally sensitive water-soluble P fraction. The overlapping in situ extraction and hydrolysis method provides a relative scale of chemical and biological stability of the released P. The phytase-hydrolysable P assay provides more information about on-farm P management than just knowing total P content of the manures. The assay’s simplicity and robustness over the wide range of manure characteristics may increase routine evaluation of whole-farm accumulation of environmentally sensitive P forms. As extracellular phosphohydrolases are ubiquitous in the environment, biological and biochemical mechanisms more adequately reflect the availability of manure and soil P pools to soil microorganisms and plants over time. Moreover, these mechanisms can reveal the underlying potential for the timed release of potentially bioactive P and protracted impairment of aquatic ecosystems by agricultural P released to the environment.