Agronomic biofortification of cereals and legumes with iron, zinc, calcium and magnesium for food and nutrition security: Available options for farmers in Sub-Saharan Africa

Although agronomic biofortification has been argued as strategic approach to cope with food and nutrition insecurity in many areas, smallholders' farmers in sub-Saharan Africa (SSA) are still facing challenges to produce cereals and legumes rich in micro nutrients such as iron, zinc, calcium and magnesium. This paper review progress made in agronomic biofortification in cereals (maize and rice) and legumes in iron, zinc, calcium and magnesium, and discussed perspective for further researches and uses of agronomic biofortification in maize, rice and legume crops in sub-Saharan Africa. The review clearly indicated that agronomic biofortification offers many options for cereals (maize and rice) and legumes (common bean, chickpea, lentil, mung bean, cowpea, etc.) based on chemical fertilizers (ZnSO4, FeSO4, Fe-chelates, MgSO4, MgCl2, urea, NPK) and traditional nutrient sources (bioinoculants, farm yard manure, compost, cereal-legume intercropping system), nutrient application methods (seed priming, soil and foliar application), nutrient application rate and period of application that are crop dependent. Bottlenecks to its wide adoption by SSA farmers are among others the low availability of micronutrient-based fertilizers, low awareness, and low financial capacity. Current trends in SSA agriculture support agroecological farming based on the use of local sources of micronutrients and strategies such as compost tea, organic manure, intensive production system, coated fertilizers with plant growth promoting bacteria, plant residue incorporation, cereal-legumes intercropping. Further research should focus on the effectiveness of different agroecological strategies/sources of micronutrients along with their content in micronutrients, the availability/translocation of these micronutrients in the plants, the application time and quality of harvested products.