Forms and distribution of microelements in some Ethiopian soils

Different extracting solutions were applied to determine the forms of six m icroelements (B, Cu, Fe, Mn, Mo and Zn) existing in seven Ethiopian soil pr ofiles representative of the different pedo-climatic conditions of the coun try. The total content obtained by complete soil mineralization was compare d with forms readily soluble (ammonium acetate), easily exchangeable (aceti c acid), chelated or bioavailable (EDTA), occluded (oxalate), or adsorbed o n soil organic matter (pyrophosphate). Extractable Fe, Mn, and Zn were sign ificantly higher than that recorded elsewhere in literature, whereas B and Mo were as average values. Extractable Cu was instead lower than the litera ture values. The largest quantities of extractable microelements were obtai ned by the Tamm's ammonium-oxalate solution indicating that they are occlud ed in inorganic oxide forms. The content of chelated microelements or that complexed with organic matter were relatively lower and followed organic ma tter turnover which was particularly rapid in lowland soils with hotter cli mate. This study shows that though microelements are abundant in the Ethiop ian soils their environmental availability is limited due to their occlusio n in mineral oxides.