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Differences Among Some North American Soils in the Rate of Reaction with Phosphate¹

ABSTRACT

The results of C. G. Enfield and B. E. Bledsoe for the reaction between phosphate solutions and 25 North American soils were re-examined by plotting log concentration against log-time. This showed that the soils fell into two distinct groups. For most calcareous soils, widely differing initial concentrations of phosphate all tended to slowly decrease to a common concentration. This suggested that concentration was controlled by a solubility product. The second group was mostly noncalcareous. For these, the changes in concentration were closely described by an equation in which the effects on adsorption of both concentration and time were described by exponent terms. In contrast to previously studied Australian soils, there were large differences between the soils in the values of the two exponent terms. These reflect differences between the soils in the way they respond to increases in concentration of phosphate and to increases in period of reaction. These differences would be important in determining the amount of phosphate that could be stored by these soils. Values for the two exponents, over the range of soils, were correlated. The correlation appeared consistent with other published values.

Key Words: solubility product • precipitation • phosphate modeling • Freundlich equation • isotherms

¹ Contribution from the Division of Land Resources Management, CSIRO, Private Bag, P.O., Wembley, Western Australia, 6014.

² Senior Principal Research Scientist, CSIRO, Wembley, Western Australia.

Received for publication November 26, 1979.