Managing Soils to Alleviate Dietary Micronutrient Deficiencies in Southern Africa: Possibilities and Knowledge Gaps

Keywords: agronomic biofortification, geospatial nutrient variations, Malawi, micronutrient malnutrition, smallholder farmers, Zimbabwe.

Dietary deficiencies of mineral micronutrients including iodine (I), iron (Fe), selenium (Se), and zinc (Zn), remain prevalent especially in developing countries. In Southern Africa, human micronutrient deficiencies (MNDs) affect a majority of the population, in particular, those in rural communities who lack access to diverse diets and rely on staple grains of potentially low nutritional value. Micronutrient deficiencies are of particular concern in females of child-bearing age, infants and school children whose nutritional demands are high.

This paper reviews sources and possible causes of MNDs in Southern Africa with a specific focus on Zimbabwe and Malawi. Various strategies can be employed towards addressing this problem in communities at continued risk of deficiencies, including dietary diversification, supplements, food fortification, agronomic biofortification, and breeding. Here, we focus primarily on how fertilisers can contribute to ameliorating MNDs.

Current soil fertility management practices, including the use of traditional nitrogen (N), phosphorus (P) and potassium (K)-based fertilisers, cannot address MNDs in the region due to an inherent lack of plant-available nutrients in many soils that are important for human health. However, there is scope for judicious use of micronutrient-based fertilisers to address this problem. Our work in Zimbabwe has shown that farm-level integrated soil fertility management (ISFM) approaches, including the use of cattle manure and woodland litter combined with different Zn fertiliser formulations could increase plant-available Zn in soils and enhance grain yield and nutrition density of staple maize (Zea mays L.) and food legumes in diets of smallholder communities. In Malawi, there is considerable potential for using Se-containing fertilisers, as is practised in Finland.

We conclude that agriculture has an important role in contributing towards effective and sustainable containment of MNDs in Southern Africa. Research on fertilisers should seek to inform both agriculture and health policies to move from mere provision of adequate food to production of quality food that inclusively offers under-privileged people choices to escape the micronutrient malnutrition ‘poverty trap’ in the region. There is also a need to evaluate current fertiliser formulations that are accessible to different farmer social groups and target micronutrient-fortified fertilisers to regions that vary in their soil nutritional status.

M. Grace Manzeke Kangara, Florence Mtambanengwe, Paul Mapfumo, Soil Fertility Consortium for Southern Africa (SOFECSA), Department of Soil Science and Agricultural Engineering, University of Zimbabwe, P.O.Box MP167, Mount Pleasant, Harare, Zimbabwe.

Michael J. Watts, Inorganic Geochemistry, Centre for Environmental Geochemistry, British Geological Survey, NG12 5GG,United Kingdom.

Martin R. Broadley, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Leicestershire, LE12 5RD, United Kingdom.

32 pages, 6 figures, 1 plate, 5 tables, 138 references