Cation exchange capacity and phosphate adsortion of soils under "Cerrado" (savannah) vegetation of Amapá/Amazonian region

Abstract

The properties of cation exchange capacity and phosphate adsorption were studied in five soils under "cerrado" vegetation, collected in the Federal Territory of Amapá, Brazil. The cation exchange capacity at pH 7,0 was related to the organic matter content; the increase of CTC was about 0,5 mEq per 0,1% carbon. In the lower horizons, with low contents of organic matter, the CTC of kaolinite could be estimated as varying from 1.5 to 3.0 mEq/100 g of clay. No correlation was found between the difference of CTC measured at pH 8.2 and 7.0 with the organic carbon content. The phosphate adsorbed was correlated with the percentage of oxihydroxides of iron and aluminum. In the A horizons of the soils the average of phosphate adsorbed was 1.24 mmoles/100 g.