B. P. K. Yerima, E. Van Ranst, S. Sertsu and A. Verdoodt
Total and DTPA-extractable micronutrient cations and heavy metals were determined for some ‘vertisols and vertic inceptisols’ of the Bale Mountain area of Ethiopia. Total micronutrients and heavy metal contents in these soils were 4.8 to 11.9% Fe, 774 to 2947 ug/g Mn, 55 to 143 ug/g Zn, 5 to 65 ug/g Cu, 19 to 119 ug/g Co, 6 to 35 ug/g Pb and 0 to 4 ug/g Cd, and are generally within the ranges reported worldwide for similar soils. DTPA-extractable Fe, Mn, Zn, Cu, Co, Pb and Cd ranged from 1.81 to 17.4, 5.9 to 41.5, 0.07 to 0.37, 0.70 to 1.73, 0.07 to 0.83, 0.04 to 1.31 and 0.0 to 0.02 ug/g, respectively. Available indices of the micronutrients studied are believed to be sufficient for plant growth except Zn, which is inadequate. Available heavy metal contents are below tolerable levels that can pose danger to man and livestock. Extractable micronutrients and heavy metals generally showed a decrease in concentration with depth associated with decreasing organic carbon contents and increasing pH and CaCO3 contents that exert a major influence on the availability of the micronutrients and heavy metals. Multiple linear and quadratic regression equations generally improved the predictive abilities for available Fe, Mn, Cu, Zn and Co over simple linear relationships when pH, EC, OC and CaCO3 were used as independent variables. Regression relationships developed constitute useful predictive indices for estimating micronutrients and heavy metals from existing soil survey reports of the Bale Mountain area.
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