Dilemma of nitrogen management for future food security in sub-Saharan Africa – a review

Abstract

Abstract. Food security entails having sufficient, safe, and nutritious food to meet dietary needs. The need to optimise nitrogen (N) use for nutrition security while minimising environmental risks in sub-Saharan Africa (SSA) is overdue. Challenges related to managing N use in SSA can be associated with both insufficient use and excessive loss, and thus the continent must address the 'too little' and 'too much' paradox. Too little N is used in food production (80% of countries have N deficiencies), which has led to chronic food insecurity and malnutrition. Conversely, too much N load in water bodies due mainly to soil erosion, leaching, limited N recovery from wastewater, and atmospheric deposition contributes to eutrophication (152 Gg N year -1 in Lake Victoria, East Africa). Limited research has been conducted to improve N use for food production and adoption remains low, mainly because farming is generally practiced by resource-poor smallholder farmers. In addition, little has been done to effectively address the 'too much' issues, as a consequence of limited research capacity. This research gap must be addressed, and supportive policies operationalised, to maximise N benefits, while also minimising pollution. Innovation platforms involving key stakeholders are required to address N use efficiency along the food supply chain in SSA, as well as other world regions with similar challenges.

Spatial trends in the nitrogen budget of the African agro-food system over the past five decades

“…Most African countries failed to achieve the 6-fold increase in fertilizer use (at a rate of 50 kg ha −1 yr −1 ) by 2015 (Masso et al 2017) as recommended by The Alliance for a Green Revolution in Africa (AGRA) (Toenniessen et al 2008). In Africa, fertilizers are predominantly used to supply N (approximately 90% of fertilizers used).…”

Sustaining rural livelihoods through an integrated landscape approach

“…To compensate for the general nutrient defi cit in soils and in food in sub-Saharan Africa, it is strongly recommended to invest in a more diversifi ed agricultural system by increasing the contribution of legumes and trees on farms (Kuyah et al, 2016;Masso et al, 2017;Oborn et al, 2017). The results of our ABM simulations show that investments in agroforestry have a positive income eff ect in addition to improving soil fertility; the net present value is positive and the costbenefi t ratio is signifi cantly higher than 1.0 compared to continuous maize production without trees.…”

Efficient use of reactive nitrogen for productive agroecosystems

“…The relative price of N fertiliser compared with agricultural products also affects N-use efficiencies (Angus and Grace 2017;Liu et al 2017;Masso et al 2017;Pannell 2017). In particular, agricultural subsidies, either to reduce the price of N fertiliser or increase the price of farm products drive overuse of N fertiliser.…”

“…Even where N fertiliser is on average used sparingly, such as in sub-Saharan Africa, there is a paradox of insufficient N use causing low crop yield and human malnutrition, as well as excessive N contributing to eutrophication of iconic water bodies (Masso et al 2017). Policies to support resource-poor farmers, in combination with extension of the good agronomic practices associated with integrated soil fertility management are needed in this region (Masso et al 2017).…”

“…For example in the European Nitrogen Assessment, only one chapter deals with the relationship between the N : grain price ratio and fertiliser usage (Jensen and Schjoerring 2011). In subSaharan Africa, implementing policies to improve the quality of inputs, outputs and supply chain infrastructure, and reduce input costs, is expected to increase agronomic N efficiency (Masso et al 2017).…”