SOIL ORGANIC MATTER STUDIES: EXTRACTION WITH FORMIC ACID/DIMETHYL SULPHOXIDE MIXTURES AND FRACTIONATION WITH Zr(IV)

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Abstract
Summary: Mixtures of the dipolar organic solvents formic acid (FA) and dimethyl sulphoxide (DMSO) were used to extract organic matter from soils. At 100 °C optimum extraction from a calcareous clay loam was with 80/20 v/v FA/DMSO, corresponding to a maximum in dielectric constant.Extraction of seven soils with boiling FA/H, O (107 °C) and FA/DMSO (112 °C) indicated that similar amounts of C and N are generally dissolved by the two solvent mixtures. However, FA/DMSO was about twice as efficient as FA/H2O for the ver‐miculite‐rich, calcareous, organic clay loam, removing 66 per cent of its C and 54 per cent of its N.Zr(IV) hydroxide in acidic aqueous acetone was a better flocculant than Ti(IV) for the dissolved organic matter. Model compound studies, together with hydrolytic and NMR studies, indicated that Zr precipitates carbohydrate‐like but not aromatic organic components. The quantity of Zr sorbed to the organic matter corresponds closely with its C.E.C. determined by Ba retention.