A PHOSPHATE SORPTION INDEX FOR SOILS

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Abstract
Summary: Phosphate sorption isotherms covering a wide concentration range (10−6 to 5 × 10−3m phosphate) were determined for 42 soil samples at 20 °C by a standardized technique. The slope of a plot of the sorption, x, against the logarithm of the equilibrium solution phosphate concentration, log c, measured at c= 10−4M, proved a suitable reference index to characterize the phosphate sorbing properties of the soils. Several single‐point methods were tested by statistical correlation against this reference index. Of these, the sorption, x, from one addition of 150 mg P/100 g soil gave r= 0.951, but r= 0.974 when the equilibrium concentration was also taken into account in the quotient x/log c. This quotient is therefore suggested as a simple yet adequate way of indicating a fundamental soil property, its phosphate sorption isotherm.
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