ADSORPTION OF PHOSPHORUS BY FOUR SASKATCHEWAN SOILS

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Abstract
The adsorption of phosphorus by four soils of differing colloid content showed close agreement with the Langmuir isotherm when final phosphorus solution concentrations were less than 20 μg. P/ml. Calculated adsorption maximum for the four soils were 79.1, 87.7, 150.4 and 164.4 μg. P per g. of soil. The average value of the constant k, related to the bounding energy of the soil for phosphorus, was 0.141.The percentage phosphorus saturation of the adsorption maximum was closely correlated with the equilibrium phosphorus concentration in the soil suspension. At an equilibrium concentration of 28.7 μg. P/ml., 100 per cent saturation of the adsorption capacity of the four soils was obtained; the total adsorbed phosphorus on the four soils was not related to the phosphorus concentration of the soil solution but varied considerably depending on the colloid content of the respective soils.Carbonated water extractable phosphorus, and 'surface' phosphorus measured by P32 equilibrium studies, were not related to the equilibrium concentration of phosphorus of the soil solution. It appears that the percentage phosphorus saturation of the adsorption maximum may prove a more reliable measure of the capacity of the soil to supply phosphorus to the soil solution than either of the 'quick' tests used.Organic matter appeared to be equally as important as the inorganic colloids in determining the phosphorus adsorption capacity of the soils. Differences in exchangeable calcium were not closely related to the adsorption maximum.

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