Nitrogen management for future food security : Sub-Saharan African case-study

One of the definitions for food security is having sufficient, safe, and nutritious food to meet dietary needs. There is an overdue need to optimize nitrogen use for food and nutrition security in developing countries particularly in sub-Saharan Africa, while minimizing environmental risks. In the past, nitrogen related environmental issues have often been associated with excessive use; however, of recently, challenges related to ‘too little’ nitrogen use has been recognized. In sub-Saharan Africa, nitrogen management must address the ‘too little’ and ‘too much’ paradox. Too little nitrogen is used in food production, which has led to chronic food insecurity and malnutrition. Conversely, too much nitrogen load in water bodies due mainly to excessive soil erosion, leaching, limited nitrogen recovery from wastewater, and atmospheric deposition still contributes to eutrophication in some areas. Significant research has been conducted to improve N use for food production, whereas little has been done to effectively address the ‘too much’ issues. The current research gaps must be addressed, and supportive policies operationalized, to maximize on nitrogen benefits, while reducing its negative impacts on the environment. Innovation platforms involving key stakeholders are required to address the nitrogen use efficiency along the full food supply chain in sub-Saharan Africa, as well as other World regions with similar challenges. Introduction Africa’s agricultural lands continue being degraded with an annual estimated economic cost of up to 18% of the gross domestic product (Nkonya et al, 2011) because of poor agronomic practices and nutrient depletion (Tittonell and Giller, 2013; Sutton et al., 2013). Over 80% of agricultural lands are for instance nitrogen (N) deficient (Liu et al., 2010). Barriers such as availability and costs of inputs, poor economic returns of input use due to limited market opportunities or quality of the inputs, limited financial capacity and access to credits, and insufficient extension services among others have drastically affected adoption of improved agricultural inputs including fertilizers, of which nitrogen is just one (Akpan et al., 2012a,b; Akudugu et al., 2012). Limited research capacity in most regions of sub-Saharan Africa, particularly for long term trials, has also added to the difficulty of improving nitrogen agronomic use efficiency. Soil acidification, poor organic matter content, deficiencies of various nutrients and reduced microbial activities are among factors affecting crop responses to applied nitrogen (Fairhurst, 2012, Nezomba et al., 2015). Adequate diagnosis of the actual limiting factors to inform the application of integrated soil fertility management is therefore required to optimize N agronomic use efficiency (Giller et al., 2011) and increase the sustainability of agricultural intensification (Vanlauwe et al., 2015). Continuous nitrogen depletion has contributed not only to the persistent food insecurity for both quantity and quality (Marler and Wallin, 2006), but also excessive erosion due to insufficient land cover, deforestation, and encroachment to marginal lands, and consequently N load into water bodies (Leip et al., 2014). In highly populated regions of sub-Saharan Africa like the Lake Victoria catchment, inadequate systems for municipal wastewater treatments have also resulted in excessive N load into water bodies and contributed to eutrophication of certain sections of the Lake (LVBC, 2012; Zhou et al. 2014). Atmospheric deposition also contributes to N load into the sub-Saharan African environment including surface water (Galy-Lacaux and Delon, 2014). Other sources of N load into water bodies include erosion in infrastructure construction, runoff