Although human micronutrient deficiencies are common in Sub-Saharan Africa, we are lacking information about micronutrient contents in soils. This information is essential if we want to manage our crops to produce food with balanced micronutrient contents to meet the requirements of humans. E.g. in Finland this information has been successfully used to improve the micronutrient status of the whole population, selenium being a unique example globally.
New rapid low cost spectral methods (IR, total x-ray diffraction, total x-ray fluorescence) were developed in World Agroforestry Centre (ICRAF) for diagnosing soil micronutrient status and calibrated against traditional chemical methods (AAAc-EDTA). Soil samples collected under Africa Soil Information Service (AfSIS) are used for calibration and establishing a baseline on soil micronutrient status.
Results of over 1700 pairs of top- and subsoil samples, collected from 57 randomly located AfSIS sentinel sites covering major agro climatic zones of 19 Sub-Saharan Africa countries show no marked differences in the concentrations of the easily soluble elements between topsoil and subsoil. Using guideline values for Finnish soils, the range midpoints of the critical limits of Mn (8%), Fe (42%), Cu (48%), Zn (56%), and B (79%) in topsoils seem low relative to sufficiency guidelines for good crop growth, indicating a high prevalence of deficiencies for all micronutrients except Mn, as especially so for Boron.
We need to develop management strategies for tackling micronutrient deficiencies and study the areal correlation between soil and human deficiencies to be able to focus management practices for improving plant, animal and human health.