CHEMICAL METHODS FOR ESTIMATING THE AVAILABILITY OF SOIL PHOSPHATE

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Abstract
In studies covering 3 yr. it was found that a satisfactory estimation of the availability of phosphates by extracting with one solvent regardless of strength is not always possible. Their relative solubility in 2 solvents of different strength is a much better indication of the capacity of the soil to supply plants. A fairly reliable estimate of the phosphate-supplying power of a soil is given by extracting it with a dilute acid added in such amount that the extract has a pH of approximately 4. Very good and very poor soils are quickly and cheaply differentiated by an equilibrium test, while the percolation tests are more reliable.