How much nitrogen does Africa need to feed itself by 2050?

Abstract

Nitrogen (N) fertilizers are very important for global food self-sufficiency (FSS), particularly for Africa, where the N input in agriculture is very low. This is the first work which studies and calculates the amount of N fertilizer that each country in Africa needs to feed itself by 2050. In this study, we used five different scenarios of inorganic fertilizer N (IFN) use and human diets to calculate the amount of N fertilizer needed to achieve FSS in Africa by 2050 and analyze the changes in N budget; N losses and N use efficiency (NUE). These scenarios include 1) business as usual (BAU), 2) equitable diet (EqD; self-sufficiency), 3) an IFN input 20% less than the EqD (S1), 4) an IFN input 40% less than the EqD (S2), and 5) a 20% increase in IFN input relative to the EqD (S3). Under the BAU scenario, production trends continue as they have over the past five decades, including an unhealthy human diet. In the EqD scenario, the priority is to meet the local demand for both animal and plant proteins with a healthy human diet. Under the EqD scenario, increasing the total N input from 35 kg N ha^-1 yr^-1 to 181 kg N ha^-1 yr^-1 during 2016-2050 is needed to achieve FSS in Africa. This increase in N fertilizer use represents unprecedented N inputs to African terrestrial ecosystems - at least 52 Tg N yr^-1 - which would lead to inevitable increases in N losses. We also found that the NUE would decrease from 63% during 2010-2016 to 50% by 2050, whereas the total N surplus would increase from 13 kg N ha^-1 yr^-1 to 90 kg N ha^-1 yr^-1 by 2050. The estimated gaseous emissions would increase from 8 kg N ha^-1 yr^-1 to 61 kg N ha^-1 yr^-1 by 2050. Our findings conclude that, it is very important to consider the high N losses in Africa if the EqD scenario is applied. The S1 and S2 scenarios result in much less environmental N loss, and better NUE compared with the EqD scenario. Therefore, based on these findings we can recommend the implementation of the S2 scenario with an IFN dose of 77 kg N ha^-1 yr^-1, in parallel with the use of modern agricultural techniques and the increased use of organic inputs.

Keywords: Africa; Human diet; N loss; Nitrogen (N) budget; Self-sufficiency.