Comparison of chemical extraction methods for the determination of “available” phosphate in soils

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Abstract
The amounts of phosphate extracted by 15 methods or variants from 16 North Island soils varied widely, but many of the values were closely correlated with each other. Correlations between the soil test values and the inorganic soil phosphate fractions indicated that many of the methods extracted only aluminium- and/or calcium-bound phosphate. Although values obtained by the Truog method, at present in use in the Department of Agriculture0027s soil testing laboratories, were significantly correlated with yield and phosphorus uptake of white clover in the glasshouse, several other methods showed better correlations with the plant data and gave a more accurate estimate of the phosphate status of the soils under study. Of the alternative methods, those of Bray particularly appeal as being practical and rapid.