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An effective water extraction method for the determination of plant-available soil phosphorus

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A new variant of the water-extraction method for the assessment of soil phosphorus availability to the plant was recently developed by Van der Paauw and Sissingh. The correlation between the water-extractable soil phosphate (Pw value) and the response of the plant, measured in most cases by the P2O5 content of dry matter, was high on Dutch soil types and was not affected by differences in such soil factors as organic matter content, particle size content, CaCO3 content, pH, phosphate-fixation capacity and other factors related to the origin of the soil. In other words, the relationship was the same for all soil types investigated.7

In order to investigate whether an equally good result would be obtained with soil types from widely diverging origin and properties, the method was evaluated in a pot experiment with potato (tops) and spring wheat grown successively on different soil types of European, American and Australian origin.

A high correlation between Pw value and the P2O5 content of spring wheat was found, which explained 88% of the variance. All soil types of different origin could be represented by one regression line.

The dry-matter yield of wheat was also closely correlated with Pw value, although the yield was also influenced by the pH of the soil.

With potatoes a high correlation between water-extractable P and P2O5 content of the tops was found in the series of European soils, but on part of the American and Australian soils the P2O5 contents of plants were higher than those on European soils with corresponding Pw values. This difference could not be explained.

In general it may be stated that the Pw value provides a reliable estimate of the availability of soil phosphorus to the plant in a wide variety of soil types.

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van der Paauw, F. An effective water extraction method for the determination of plant-available soil phosphorus. Plant Soil 34, 467–481 (1971).

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