Total and extractable copper, iron, manganese and zinc in major agricultural soils in the Lower Benue Valley, Central Nigeria and the concept of extractant efficiency

Abstract

As a contribution to the broader national effort to evaluate the fertility and management problems of Nigeria’s major agricultural soils, total and plant-available concentrations of the micronutrients Cu Fe, Mn and Zn were determined in six profiles, representing typical agricultural soils in the Lower Benue Valley, Central Nigeria. Total amounts of the elements ranged from 2.72-49.8 mg kg^-1 for Cu and 6.50-77.5 mg kg^-1 for Zn, and 0.52-12.7 % and 46.7-1340 mg kg^-1 for Fe and Mn, respectively. More total micronutrients occurred in the soil derived from metamorphic rocks, than in the soils with sedimentary parent materials. Although the amounts of the extractable micronutrients varied with the extractant employed, using critical limits established elsewhere in Nigeria, plant-available Cu, Fe and Mn may be considered adequate, while Zn deficiency problems may be expected in some of the soils in the region. Using the proportion of total elements extracted by each extractant, a new concept of “extractant efficiency” is introduced to aid in selecting candidate extractants for soil testing.