Micronutrient deficiencies in African soils and the human nutritional nexus: opportunities with staple crops

J Kihara,M Kinyua,K Piikki,P Bolo,J Rurinda

doi:10.1007/s10653-019-00499-w

Abstract

A synthesis of available agronomic datasets and peer-reviewed scientific literature was conducted to: (1) assess the status of micronutrients in sub-Saharan Africa (SSA) arable soils, (2) improve the understanding of the relations between soil quality/management and crop nutritional quality and (3) evaluate the potential profitability of application of secondary and micronutrients to key food crops in SSA, namely maize (Zea mays L.), beans (Phaseolus spp. and Vicia faba L.), wheat (Triticum aestivum L.) and rice (Oryza sativa L.). We found that there is evidence of widespread but varying micronutrient deficiencies in SSA arable soils and that simultaneous deficiencies of multiple elements (co-occurrence) are prevalent. Zinc (Zn) predominates the list of micronutrients that are deficient in SSA arable soils. Boron (B), iron (Fe), molybdenum (Mo) and copper (Cu) deficiencies are also common. Micronutrient fertilization/agronomic biofortification increases micronutrient concentrations in edible plant organs, and it was profitable to apply fertilizers containing micronutrient elements in 60–80% of the cases. However, both the plant nutritional quality and profit had large variations. Possible causes of this variation may be differences in crop species and cultivars, fertilizer type and application methods, climate and initial soil conditions, and soil chemistry effects on nutrient availability for crop uptake. Therefore, micronutrient use efficiency can be improved by adapting the rates and types of fertilizers to site-specific soil and management conditions. To make region-wide nutritional changes using agronomic biofortification, major policy interventions are needed.

Highlights

Soil nutrients status and management determine crop productivity but nutrients concentration in plant parts consumed as food and feed
Previous review on micronutrient problems in west Africa pointed to boron, zinc and molybdenum deficiencies as the most prevalent (Abe et al 2010; Buri et al 2000), while the highest deficiencies for boron and copper occur in the subhumid zones (Hengl et al 2017)
Deficiencies of secondary and micronutrients are associated with continued mining by crops because of non-application of these nutrients in production, there is no long-term data in sub-Saharan Africa (SSA) to show their trends in the soil

Summary

Introduction

Soil nutrients status and management determine crop productivity but nutrients concentration in plant parts consumed as food and feed. About one-third of arable soils are deficient in micronutrients, in zinc (Zn) (Cakmak et al 2017), and this eventually affects human nutrition. The problem of micronutrient deficiencies in soils (often involving 2–5 micronutrients at a time) is widespread in SSA (Berkhout et al 2017; Hengl et al 2017). This is mainly a result of decades of soil degradation and low and unbalanced application of fertilizers mostly of nitrogen (N), phosphorous (P) and potassium (K). The importance of micronutrients in crop productivity was recently demonstrated (Kihara et al 2017), but a huge gap remains in understanding their links to nutrition

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Conclusion