Phosphate fixation in soils from the state of Rio de Janeiro

Abstract

The fixation of phosphate was studied using samples of forty soils from the state of Rio de Janeiro. The soils were equilibrated with solution of KH₂PO₄ 10^-3 M, and the fixed phosphate were determined by the difference between the initial and final concentration of solution. The phosphate fixation varied from 0.05 to 1.89 mmols/100 g of soil. These limits corresponded to 1 to 37,8% of the applied phosphate, respectively, with averages of 23.5% for the Red-Yellow Latosols, 21.5% for the Hydromorphics and Alluvials, 16.3% for the Red-Yellow Podzolics and 4.7% for the soils derived from the sediments of the terciary ("Tabuleiro" soils). The phosphate fixation values, in percentage, were closely correlated with the amounts of clay, moisture, organic matter, oxy-hydroxyds of aluminum and pH in KCI.