Self‐Diffusion Coefficients of Phosphorus in Soil Measured by Transient and Steady‐State Methods

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Abstract
Self‐diffusion coefficients of P in soil were measured by two independent methods and by calculating Dp from chloride diffusion. All three methods yielded similar values for Dp at low moisture suctions. On Apishapa silty clay loam, values of Dp ranged from 0.4 × 10‐7 to 15.5 × 10‐7 cm2/sec as the volumetric moisture content increased from 0.22 to 0.55, or as the soil moisture suction decreased from 6 to < 0.1 bar. From these values of Dp a self‐diffusion coefficient for P in bulk solution was calculated, which agreed closely with the experimentally measured value. The transient state method required a separate evaluation of a capacity factor which varied between 100 to 300. If this capacity factor had been omitted, the apparent Dp would have been smaller by 100‐ to 300‐fold. These results demonstrate the necessity of measuring a capacity factor when Dp is to be determined by a transient state method.

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