SEGH Articles

Notes from Malawi

07 November 2012
Plant and crop selenium concentration shows strong geochemical control, and our data suggests widespread high prevalence of dietary Se deficiency across Malawi, primarily due to the low pH of the predominant soil types causing Se to be held in an unavailable form.

As previously documented on this website

(http://segh.net/articles/Ecosystem_services_to_alleviate_micronutrient_malnutrition_in_Sub_Saharan_Africa/), the British Geological Survey (BGS), the University of Nottingham (UoN) and the Malawian Ministry of Agriculture are working to improve

understanding of mineral intake levels in Malawi and explore options for addressing deficiencies. Plant and crop selenium (Se) concentration shows strong geochemical control, and our data suggests widespread high prevalence of dietary Se deficiency across Malawi, primarily due to the low pH of the predominant soil types which causes Se to be held in an unavailable form.

Selenium is only required in very small quantities – the daily dietary requirement for the whole population of Africa is around 50kg. One option would be to supplement fertilisers with tiny amounts of Se, a policy that was adopted in Finland in the 1980s. Our field trials in Malawi have shown this to be potentially effective in raising maize grain Se levels (Chillimba et al. 2011). Wider testing is now required considering the variety of cropping systems found around the country, and that many farmers are unable to afford fertiliser.Malawian Ministry of Agriculture are working to improve the understanding of mineral intake levels in Malawi and explore options for addressing deficiencies. Plant and crop selenium (Se) concentration shows strong geochemical control, and our data suggests widespread high prevalence of dietary Se deficiency across Malawi, primarily due to the low pH of the predominant soil types which causes Se to be held in an unavailable form.

Another option is liming, which I will be testing with maize field trials this year at three locations in central and northern Malawi.  By increasing soil pH, liming has the potential to improve Se availability and hence increase plant uptake.  Liming might also provide economic benefits to farmers. A BGS-led study in Zambia (FarmLime) showed that liming rates around 0.5-1 tonne per hectare can increase maize and groundnut yields, with a positive cost-benefit ratio. However, the affordability and availability of lime depends greatly on proximity to the lime source, and many farmers struggle to afford inputs due to lack of credit. In addition, we expect that improvements in grain Se content might only be seen at much higher levels of liming.

Finally, we are exploring options for meeting dietary requirements of Se (and many other minerals, including calcium, iodine and zinc) through dietary diversification. In order to help inform this study, I have been busy collecting food samples from around Malawi which will be shipped back to the UK and analysed at BGS and UoN for mineral content. At this time of year, near the end of the dry season, most households are relying on grain stocks from May’s harvest. This means maize for most, although pearl millet and sorghum are preferred in the Shire valley in the south due to their drought tolerance. Grain is generally milled at local mills and boiled in water to prepare a thick porridge, which is accompanied by a “relish” of boiled leaves, beans, or sometimes fish from Lake Malawi. Most households collect vegetable leaves during the rainy season (including pumpkin leaves, bean leaves and the leaves of many different indigenous vegetables such as “chisoso” and “tove”), with some cooked fresh and some sun-dried in order to have supplies through the dry season. For all food samples collected, we also take a coupled soil sample. This will help to identify the influence of soil geochemistry on crop mineral content.

The planting rains are due soon, working their way up from the south, and farmers are busy preparing their maize ridges with hand hoes. It’s an exciting time of year, though slightly nail-biting as planting too early or too late can lead to crop failure. Farmers around Mzuzu where I am staying have found climate change, especially unpredictable rainfall patterns, a major challenge in recent years. Their anecdotal evidence of a warming climate and shorter rains fits with empirical data (http://mtc-m17.sid.inpe.br/col/sid.inpe.br/mtc-m17@80/2006/11.27.17.33/doc/Coelho.Evidence.pdf ).

All our fieldwork is done through the Malawi Ministry of Agriculture. As well as the obvious advantages garnered through local knowledge, contacts and resources, the setup also provides a route for information dissemination through the agricultural extension offices, a major source of support for most farmers.

Conducting research in Malawi does throw up some logistical difficulties, such as the fairly frequent fuel shortages. But in a country where the majority of people are involved in agriculture, mainly for subsistence, and where many households are just one poor harvest away from hunger, agricultural research can greatly help farmers through provision of information. Particularly in a subsistence context and given Malawi’s health and nutrition indicators (such as almost half children under five years of age are medically classed as “wasted”, and almost half non-pregnant women aged 15-49 are anaemic), agricultural policy and interventions need to aim for nutritional benefits, not just focus on yields.

Edward Joy

University of Nottingham – British Geological Survey – Ministry of Agriculture, Malawi.

Chilimba, A.D.C., Young, S.D., Black, C.R., Ander, E.L., Watts, M.J., Lammel, J. and Broadley, M.R. 2011. Maize grain and soil surveys reveal suboptimal dietary selenium intake is widespread in Malawi, Scientific Reports, 1, 1 - 9. http://www.nature.com/srep/2011/110823/srep00072/full/srep00072.html

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