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ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Publications at this Location » Publication #152835
Title: QUANTIFICATION OF MYO-INOSITOL HEXAKISPHOSPHATE IN ALKALINE SOIL EXTRACTS BY SOLUTION PHOSPHORUS 31 NMR SPECTROSCOPY AND SPECTRAL DECONVULTION

Author
item Turner, Benjamin
item MAHIEU, NATHALIE - UNIVERSITY OF LONDON
item CONDRON, LEO - LINCOLN UNIV,NEW ZEALAND

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2003
Publication Date: 7/1/2003
Citation: Turner, B.L., Mahieu, N., Condron, L.M. Quantification of myo-inositol hexakisphosphate in alkaline soil extracts by solution 31P NMR spectroscopy and spectral deconvolution. Soil Science. 2003. v. 168. p. 1-10.

Interpretive Summary: Inositol phosphates are the dominant class of organic phosphorus (P) compounds in most soils, but are poorly understood because they are not easily identified in soil extracts. This study reports a relatively simple technique using solution phosphorus 31 NMR spectroscopy and spectral deconvolution for the quantification of myo-inositol hexakisphosphate (phytic acid), the most abundant soil inositol phosphate, in alkaline soil extracts. Application of the technique to a range of permanent pasture soils from England and Wales suggests that phytic acid accumulates in soils by mechanisms at least partially independent of those controlling organic matter stabilization and dynamics. Furthermore, biological P availability may partly regulate phytic acid concentrations in soils, perhaps because organisms capable of degrading this compound are favoured in more P-limited environments.

Technical Abstract: Inositol phosphates are the dominant class of organic phosphorus (P) compounds in most soils, but are poorly understood because they are not easily identified in soil extracts. This study reports a relatively simple technique using solution phosphorus 31 NMR spectroscopy and spectral deconvolution for the quantification of myo-inositol hexakisphosphate (phytic acid), the most abundant soil inositol phosphate, in alkaline soil extracts. An authentic myo-inositol hexakisphosphate standard added to a re-dissolved soil extract gave signals at 5.85, 4.92, 4.55, and 4.43 ppm in the ratio 1:2:2:1. Spectral deconvolution accurately quantified these signals (102 plus/minus 4%) in solutions containing a mixture of model P compounds by resolving the envelope of signals in the orthophosphate monoester region. In NaOH-EDTA extracts of a range of lowland permanent pasture soils from England and Wales, concentrations of myo-inositol hexakisphosphate determined by spectral deconvolution ranged between 26 and 189 mg P per kg soil, equivalent to between 11 and 35% of the extracted organic P. Concentrations were positively correlated with oxalate-extractable aluminium and iron, but were not correlated with total carbon, total nitrogen, clay, or the microbial biomass. This suggests that myo-inositol hexakisphosphate accumulates in soils by mechanisms at least partially independent of those controlling organic matter stabilization and dynamics. Furthermore, myo-inositol hexakisphosphate concentrations were positively correlated with plant-available inorganic P and negatively correlated with the carbon-to-organic P ratio, suggesting that biological P availability may partly regulate myo-inositol hexakisphosphate concentrations in soils, perhaps because organisms capable of degrading this compound are favoured in more P-limited environments. Solution 31P NMR spectroscopy and spectral deconvolution offers a relatively simple method of quantifying myo-inositol hexakisphosphate in soil extracts.