TRACE-ELEMENTS IN SOME NORTHERN NIGERIAN SOILS

The concentrations of the more-or-less strongly retained trace elements present in the root zone of some northern Nigerian soils were determined. The soils were chosen to represent some of the more extensively distributed soil orders under cultivation in the Nigerian savanna zone. Extraction by concentrated HNO3 was used to determine the so-called ''total'' amount of retained Cu, Zn, Pb, Ni, Cd, and B in the soils. Aqueous solutions of the chelating agents, EDTA and DTPA, were used to extract the more weakly retained Cu, Zn, Pb, Ni, and Cd; whereas, hot water was used to extract the weakly retained B. The ''total'' and the more-weakly-retained contents of these trace elements were significantly correlated with the amount of clay, silt, and the oxalate-extractable oxyhydroxides present in the soils; whereas, only the weakly retained elements were significantly correlated with the content of organic matter in the soil. Both the ''total'' concentrations and weakly-retained Cu, Zn, and B were so low that deficiency problems may develop in these sandy soils if cultivated more intensively on a commercial scale without due precautions. The concentrations of the weakly-retained toxic elements, Pb, Ni, and Cd, were low indicating that industrial pollution has not yet occurred.