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Kinetic Behavior of Phosphate Sorption by Acid, Sandy Soil¹

ABSTRACT

The time dependency of phosphate sorption-desorption in fertilized soil is particularly important to the efficiency with which plant roots absorb applied phosphorus from the soil solution. In this study, phosphorus sorption by two acid, sandy soils was measured with time using a laboratory batch technique for a range of initial phosphorus concentrations in solution. A comparison of experimental data with results calculated using a two-site sorption-desorption model showed that for contactimes > 1 hour the observed phosphorus sorption in both these sandy soils could be described by assuming rapid and slow reversible reactions to occur simultaneously at two separate types of sorption sites. However, for shorter contact times (< 1 hour) the 2-site model did not describe the P sorption adequately. The orders of the forward reactions at the rapid and slow sorption sites were fractional and first-order, respectively, with regard to the P concentration in solution. For a given soil, one set of rate coefficient values was sufficient to describe the solution phase concentration of P for several different initial concentrations.

Key Words: spodosols • inorganic phosphorus

¹ Research was supported in part by Grant no. R800517 from the USEPA. This paper is published as Florida Agric. Exp. Stn. Journal Series Paper no. 1599.

² Professor, Professor, and Research Associate in the Soil Science Dep., and Associate Professor in the Dep. of Statistics, respectively, Univ. of Florida, Gainesville, FL 32611. The third author is currently an Assistant Professor in the Agronomy Dep. at Louisiana State Univ.

Received for publication December 8, 1978.