Distribution and availability of iron, manganese, zinc, and copper in four tropical agricultural soils

Information on micronutrient status in soils of West Africa is extremely scarce. Distribution and availability of iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) in surface horizons of four Malian agricultural soils (Bougouni, Kangaba, Baguineda, and Gao, abbreviated as Bgni, Kgba, Bgda, and Gao) were studied. The soils contained relatively low amounts of total Mn, Zn, and Cu. Total Zn and Cu were below the Dutch reference A value established for clean soil. The fractionation of Mn, Fe, Zn, and Cu allowed the estimation of the availability of metals for uptake. Readily available Fe and Mn exceeded critical levels in all soils. Readily available Zn and Cu in contrast were below critical levels for plant growth. Plants may have serious deficiencies of these elements. Iron, Mn, and Zn (Bgda and Gao) were mostly found in the residual fraction while Cu was mostly found in organic fractions. The fractionation allowed also the estimate of the potential for contamination of groundwater after rainfall.