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United States Department of Agriculture

Agricultural Research Service

Research Project: DEVELOPING TOOLS TO PREDICT ATMOSPHERIC FATE OF VOC & ODORANT EMISSIONS FROM AG OPERATIONS Title: Physical and Potentiometric Constant of Ferrous and Ferric Phytate Applied to Organic Phosphate Transport in Poorly Drained Soil

Authors
item Heighton, Lynn - UNIV OF MD, UMCES-CBL
item Schmidt, Walter

Submitted to: Electronic Publication
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 11, 2005
Publication Date: August 16, 2005
Citation: Heighton, L.P., Schmidt, W.F. 2005. Physical and potentiometric constant of ferrous and ferric phytate applied to organic phosphate transport in poorly drained soil. Electronic Publication. p. 1-53.

Interpretive Summary: More than half of the phosphorus (P) in agricultural soils from organic matter is in the form of organic P, primarily phytate. Iron is abundant in many soils and can have a cationic charge of +2 (ferrous ions) or +3 (ferric ions). Since phytate molecules in soils as anions will have a negative charge normally between -4 and -9, phytate can easily form complexes ferric and ferrous complexes. Ferrous phytate was found to form quickly and persist for a longer period then ferric phytate. Dissociation constants were 1.113 and 1.186 and formation constants were 0.899 and 0.843 for ferric and ferrous phytate respectively. Redox potential of soils correlates with the ratio of Fe+2/Fe+3 in soils. Thus, the redox potential and concentration of iron were measured in a soil column containing a benchmark poorly drained soil from Maryland (Elkton). Enzymatic dephosphoralation recoveries supported the magnitude of the kinetic and equilibrium rate constants.

Technical Abstract: Inositol phosphates are metabolically derived organic phosphates that increasingly appear to be an important sink and source of phosphate in the environment. Inositol hexakis dihydrogen phosphate or phytic acid is the most common inositol phosphate in the environment. Iron is abundant in many terrestrial systems. Mobility of phytic acid iron complexes are potentially pH and redox responsive. Ferric and ferrous complexes of phytic acid were investigated by proton nuclear magnetic resonance spectroscopy, enzymatic dephosphoralation and potentiometrically in solution. The redox potential and concentration of iron were measured in a soil column containing a benchmark poorly drained soil from Maryland (Elkton). Ferrous phytate was found to form quickly and persist for a longer period then ferric phytate. Dissociation constants were 1.113 and 1.186 and formation constants were 0.899 and 0.843 for ferric and ferrous phytate respectively. Enzymatic dephosphoralation recoveries supported the magnitude of the kinetic and equilibrium rate constants.

Last Modified: 9/20/2014
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