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item Dao, Thanh

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/2/2003
Publication Date: 11/2/2003
Citation: Dao, T.H. 2003. How dietary phytases can increase manure organic phosphorus mobilization [abstract]. American Society of Agronomy Annual Meeting Abstracts CD-ROM. No. S11-dao381545-P.

Interpretive Summary:

Technical Abstract: Animal manure contains partially digested feed fiber and grains where phosphorus is bound in organic compounds that include phytic acid (IP6). Information is needed on the controlling mechanisms and effects of other (non-IP6) organic ligands (LIGND) on the dephosphorylation of IP6 that is a potential source of dissolved P in the soil-manure-water system. The bioavailability and potential ecological effect of IP6-P were regulated by pH-controlled activity of exogeneous phytases and by the associated counterions. The polydentate IP6 has the potential for forming monomeric and polymeric compounds with multivalent counterions. Complexation can limit the hydrolytic activity of phytases and the hydrolysis of IP6. Dephosphorylation of IP6 in standard solutions, dairy wastewater, and poultry manure followed a first-order decay rate model. However, increased recovery of PO4-P over and above the quantity of added IP6-P by exogenous phytases suggested the extensive presence of manure organic phosphate monoesters. The phytase-hydrolyzable P (PHP) fraction was actually 40% and higher than that measured without using non-IP6 ligands such as EDTA, CDTA, or DTPA. The results suggested that non-IP6 ligands-induced changes increase the mobilization of complexed organic P, above and beyond the simple dissolution of inorganic phosphates. Manure from livestock fed rations containing phytases can be high in IP6-derived dissolved P, in addition to mineral dietary P. The IP6 mobilization leads to a greater susceptibility to enzymatic dephosphorylation, and increase the potential for release and environmental dispersion of PHP.