Oxalate extraction and determination by ionic chromatography in calcareous soils and in mycorrhized roots environment

Abstract Secreted by mushrooms, oxalic acid plays a basic role in calcareous soils by trapping calcium (Ca) and releasing phosphorus (P). The assessment of this organic anion requires an extraction step before analysis. A theoretical study, with GEOCHEM software, emphasizes the complexing properties of oxalate towards Ca and Al at pH> 1.5, and especially for ferric iron (Fe III) at very acidic pH (< 0.5), thus complicating its quantitation; it also specifies the experimental conditions for extracting soil calcium oxalate and avoiding the Fe(III) interference. A simple and quick method is proposed for the calcium oxalate solubilization by mixing for 1 hour 5 grams of soil with boiling 1M HC1, the volume depending on sample calcareous, Al and Fe content, and adding a reducing agent (hydroxylamine) of ferric iron. A fast stirring with a H+‐resin puts the resulting solution in good conditions for ionic chromatography analysis.The efficiency of this method is measured by the rate of recovery (93 to 101 %) of k...