Assessment of Fe(II), Fe(III) and Al(III) in a mineralogical profile of Gabonese soil

Four depths of a soil were sampled, extracted successively with water, 1 N KCl and aqua regia and analyzed. The soil displays a lithogenic discontinuity with a soil profile which was loam, sandy loam or clay. It was from slightly acid to strongly acid. Data showed significant correlations between soil properties and antagonist effects between Fe ions in the iron oxide formation. Metal speciation by a three extraction scheme showed that the total concentration of Fe(II) in the four soil horizons decreased as function of depth when the concentration of Al(III) and Fe(III) increased in the same time. The mineralogical fraction, the bigger fraction, decreased for all elements studied. This change led to increase significatively the water-soluble and exchangeable fractions of Fe(II) and exchangeable fraction of Al(III) and Fe(III). Significant correlations indicated inter-dependence of fractions and showed the influence of soil properties on the solubility and mobility of aluminum and iron. Keywords: acid soils; metals; sequential extractio