PHOSPHATE RELEASE FROM FERTILIZED SOILS AND ITS EFFECT ON THE CHANGES OF PHOSPHATE CONCENTRATION IN SOIL SOLUTION

The release of phosphate already present, and the sorption of further added phosphate, was studied in nineteen previously-fertilized Argentinean soils. The changes with time of the phosphate concentration in the soil solution were used as a measure of the reaction between soils and phosphate. Release of phosphate from the soils with time affected both the magnitude and the direction of the changes of the phosphate concentration in the solution. These changes differed between soils and, for a given soil, between levels of further added phosphate. The results suggest that, at high levels of further additions, the dominant effect of period of incubation is on the retention of phosphate and the concentration in solution decreased with time. At low levels of addition, the release of phosphate from the surface dominated and the concentration of phosphate in solution increased with time. Descriptive equation which considers simultaneously both sorption and release of phosphate from the soil was used. This equation is consistent with a mechanistic model of the adsorption-desorption process. © 1990 Kluwer Academic Publishers.