Desorption of phosphate in oxisols covered by humid brushland cerrado. I. The reversibility of the adsorption isotherm with respect to phosphate concentration.

Abstract

Studies were conducted in oxisols under cerrado (savannah) vegetation to investigate the reversibility of the isotherm with respect to phosphate concentration. This was achieved by replacing the equilibrium H₂HPO₄ solutions by 0.2M KCl at the same pH and temperature. Successive extractions with 0,02M KCl showed a definitive influence of the isotherm region on phosphate desorption decreasing in the order: Region III > Region II > Region I. The amounts of phosphate desorbed decreased rapidly in the successive 0,02M KCl extractions, the first two extractions desorbing approximately 50% of the total desorbed in six extractions. It was suggested that for this particular situation (P-adsorbed), the successive soil P extractions seemed a satisfactory general means of measuring the capacity factor, i.e., the soil to continue to supply phosphorus to the soil solution.