Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/25/2001
Publication Date: 11/3/2001
Citation: DAO, T.H., SCHMIDT, W.F. CA (II) AMENDMENT EFFECTS ON PHYTATE-PHOSPHORUS HYDROLYSIS. AGRONOMY ABSTRACTS. 2001. Interpretive Summary:
Technical Abstract: Phytic acid (myo-inositol-1,2,3,5/4,6-hexakis phosphate) typically accounts for 60 to 90% of stored reserves of phosphorus (P) in cereals, soybean, or corn used in animal feeds, and is hydrolyzed by extracellular enzymes. The conjugate anion, phytate (PA), has a high affinity for polyvalent cations, forms insoluble precipitates, which lower the bioavailability of P and increased complexed PA excretion in manure. To improve our understanding of the contribution of PA and organic polyphosphates to sinks and sources of PO4-P in the soil-manure-plant system, the effects of Na[I], Ca[II], Al[III], and Fe[III] and three cation to phytate-P mole ratios on the enzymatic hydrolysis of PA was measured in a buffer of pH 4.5. Phytate- and PO4-P were determined by liquid chromatography. The dephosphorylation of Na(I) phytate followed a first-order decay rate equation. Ca(II) activated the process, enhancing the rate of PO4-P release, in comparison to Na(I), Al(III), and Fe(III). Phytate hydrolysis rate remained high at Ca(II) to PA-P mole ratios up to 3:6. As cation to PA-P concentrations reached the theoretical 6 to 6 ratio, PA disappearance and accumulation of PO4-P significantly decreased, particularly for Fe(III) and Al(III) mixtures. These results suggested that the nature of the polyvalent cation and its concentration control the PA physical state in solution and persistence in manure and where manure is land applied.