• Energy Research

Significance The question whether sub-Saharan Africa (SSA) can be self-sufficient in cereals by 2050 is of global relevance. Currently, SSA is amongst the (sub)continents with the largest gap between cereal consumption and production, whereas its projected tripling demand between 2010 and 2050 is much greater than in other continents. We show that nearly complete closure of the gap between current farm yields and yield potential is needed to maintain the current level of cereal self-sufficiency (approximately 80%) by 2050. For all countries, such yield gap closure requires a large, abrupt acceleration in rate of yield increase. If this acceleration is not achieved, massive cropland expansion with attendant biodiversity loss and greenhouse gas emissions or vast import dependency are to be expected.

Nutrient limitation is a major constraint in crop production in sub-Saharan Africa (SSA). Here, we propose a generic and simple equilibrium model to estimate minimum input requirements of nitrogen, phosphorus and potassium for target yields in cereal crops under highly efficient management. The model was combined with Global Yield Gap Atlas data to explore minimum input requirements for self-sufficiency in 2050 for maize in nine countries in SSA. We estimate that yields have to increase from the current ca. 20% of water-limited yield potential to approximately 50–75% of the potential depending on the scenario investigated. Minimum nutrient input requirements must rise disproportionately more, with N input increasing 9-fold or 15-fold, because current production largely relies on soil nutrient mining, which cannot be sustained into the future.

AbstractCropping is responsible for substantial emissions of greenhouse gasses (GHGs) worldwide through the use of fertilizers and through expansion of agricultural land and associated carbon losses. Especially in sub‐Saharan Africa (SSA), GHG emissions from these processes might increase steeply in coming decades, due to tripling demand for food until 2050 to match the steep population growth. This study assesses the impact of achieving cereal self‐sufficiency by the year 2050 for 10 SSA countries on GHG emissions related to different scenarios of increasing cereal production, ranging from intensifying production to agricultural area expansion. We also assessed different nutrient management variants in the intensification. Our analysis revealed that irrespective of intensification or extensification, GHG emissions of the 10 countries jointly are at least 50% higher in 2050 than in 2015. Intensification will come, depending on the nutrient use efficiency achieved, with large increases in nutrient inputs and associated GHG emissions. However, matching food demand through conversion of forest and grasslands to cereal area likely results in much higher GHG emissions. Moreover, many countries lack enough suitable land for cereal expansion to match food demand. In addition, we analysed the uncertainty in our GHG estimates and found that it is caused primarily by uncertainty in the IPCC Tier 1 coefficient for direct N2O emissions, and by the agronomic nitrogen use efficiency (N‐AE). In conclusion, intensification scenarios are clearly superior to expansion scenarios in terms of climate change mitigation, but only if current N‐AE is increased to levels commonly achieved in, for example, the United States, and which have been demonstrated to be feasible in some locations in SSA. As such, intensifying cereal production with good agronomy and nutrient management is essential to moderate inevitable increases in GHG emissions. Sustainably increasing crop production in SSA is therefore a daunting challenge in the coming decades.

The dataset described includes second bias corrected daily weather data using ground-based weather data and simulated crop growth data under potential and water-limited potential conditions for 109 sites across ten countries in SSA including Burkina Faso, Ghana, Mali, Niger, Nigeria, Ethiopia, Kenya, Tanzania, Uganda, and Zambia. Whereas the weather data covers all sites, the simulated growth data for the four crops (maize, millet, sorghum, wheat) covers subsets of the sites depending on the geographic distribution of cultivation areas for the given crop. The stations can represent 65% of the harvested area for maize, 90% for millet, 83% for sorghum, and 59% for wheat the four crops together can represent 72% of the total harvested area in those countries. The data covers three time periods: historical (1995-2014), 2030 (2020-2039), and 2050 (2040-2059).

AbstractFood security interventions and policies need reliable estimates of crop production and the scope to enhance production on existing cropland. Here we assess the performance of two widely used ‘top-down’ gridded frameworks (Global Agro-ecological Zones and Agricultural Model Intercomparison and Improvement Project) versus an alternative ‘bottom-up’ approach (Global Yield Gap Atlas). The Global Yield Gap Atlas estimates extra production potential locally for a number of sites representing major breadbaskets and then upscales the results to larger spatial scales. We find that estimates from top-down frameworks are alarmingly unlikely, with estimated potential production being lower than current farm production at some locations. The consequences of using these coarse estimates to predict food security are illustrated by an example for sub-Saharan Africa, where using different approaches would lead to different prognoses about future cereal self-sufficiency. Our study shows that foresight about food security and associated agriculture research priority setting based on yield potential and yield gaps derived from top-down approaches are subject to a high degree of uncertainty and would benefit from incorporating estimates from bottom-up approaches.

To mitigate climate change, greenhouse gas emissions from the agricultural sector need to decrease. In this light, increasing agronomic use efficiency of nitrogen (N) application (i.e., additional grain yield per kg of N applied) is a promising avenue to attain similar yields with less inputs in regions such as Europe (with high N inputs). In contrast, on the African continent, N inputs need to increase to raise yields, which may contribute to improved food security and prevent land use change. In such case, increasing agronomic N use efficiency (N-AE) and simultaneously increasing N inputs can also be a mitigation strategy by decreasing losses to the environment and improving profitability. In both contexts, it is relevant to understand how much N-AE can be increased in a certain location, compared to the current status, and which N source (organic and/or mineral fertilizer) will be most efficient. In this working paper we present ongoing work on N benchmarking from the crop nutrient gap project (full name: Bringing Climate Smart Agriculture practices to scale: assessing their contributions to narrow nutrient and yield gaps). First, we compare current observed N-AE to the values they could potentially reach under optimal agronomic management. For this, we propose a new benchmarking method based on recent insights on the shape of N response curves and introduce the related ‘degree of good agronomy’. Second, we compare the performance of mineral versus organic fertilizers for cereal cultivation on two continents (Europe and sub-Saharan Africa) based on large number of field experiments. Finally, we assess whether and how N-AE of mineral N fertilizer can be improved when combined with organic amendments. Preliminary findings show that the proposed benchmarking method can work but relies on availability of data on soil N supply, potential yield and attainable yields. Currently, this information is sparsely available which might be a barrier for uptake of the method. We show that N supplied by mineral fertilizers is taken up more efficiently than from organic sources, with variation depending on the type of organic amendment. Variation was larger for sites in Africa than Europe, which makes targeted fertilizer strategies less straightforward. Based on European experimental data, we show that organic amendments do not increase the N-AE of mineral fertilizer N application, most likely due to the increased total N availability. In future research, we hope to improve the data requirements for the proposed benchmarking method, assess drivers of variation for nitrogen fertilizer replacement values of organic amendments and disentangle effects of organic amendments on the efficiency of mineral fertilizer N use, while extending our analysis to tropical regions.