Orthophosphate and phytate extraction from soil components by common soil phosphorus tests

• Published in: Geoderma Vol. 209-210; pp. 22 - 30
• Main Authors: Shang, C., Zelazny, L.W., Berry, D.F., Maguire, R.O.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2013
• Subjects: adsorption; Aluminum base alloys; ammonium oxalate; Argon oxygen decarburizing; calcium chloride; Degree of phosphorus saturation; Extraction; gibbsite; goethite; Kaolinite; leaching; Minerals; montmorillonite; myo-inositol; orthophosphates; Phosphorus; Phosphorus-loaded minerals; Phytate; phytic acid; prediction; risk assessment; runoff; Saturation; soil; Soil (material); Soil testing phosphorus; P; IHP; PSC; AOD; DPS; Soil testing phosphorus; Phytate; Degree of phosphorus saturation; Pi; STP; Phosphorus-loaded minerals
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2013.05.027

Chemically extractable phosphorus (P) is widely used for environmental risk assessment, because of its strong relationship with P loss through surface runoff and/or subsurface leaching. We used five common soil test extractants, water, 0.01M CaCl2, Mehlich I, Mehlich III and acidified ammonium oxalate in darkness (AOD) to recover two major P forms, orthophosphate (Pi) and phytate (inositol hexakisphosphate or IHP), which were adsorbed at various P saturation levels on Na-saturated goethite, gibbsite, kaolinite and montmorillonite. Our objective was to evaluate how the P form and mineral type influence the efficiency of these extractants to solubilize P and to examine the inter-correlations between extractable P fractions and the implications in P risk assessment. Phytate had a greater Langmuir adsorption maximum than Pi for all the studied minerals, whereas IHP had a lower extractability than Pi by all extractants. Phosphorus extractabilities increased in the order goethite<gibbsite<kaolinite<montmorillonite. Water and 0.01M CaCl2 extracted negligible IHP from all P saturation levels of these minerals. Mehlich III and AOD were equivalent in terms of the amount of P extracted. Mehlich III-P showed the best prediction of AOD-P, which is used for estimating soil degree of P saturation (DPS), whereas Mehlich I had a close relationship with AOD-P within a P form. The relationship between DPS estimated by AOD extraction and the true surface P saturation and the factors affecting the relationship were discussed in the model systems.