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The global population is projected to increase to 9 billion by mid-century, with Africa’s population doubling in the next 40 years [1]. In sub-Saharan Africa (SSA), this increasingly urbanizing population growth has failed to match equivalent increments in yields of the major crops, with increased production resulting rather from agricultural area expansion [2], very often at the expense of the natural resource base, such as carbon-rich and bio-diverse forest land (eg [3]). Major areas on the continent consequently experience nutrient limitation as a major yield gap component, especially in densely populated areas, where soil fertility regeneration through fallow periods is no longer feasible (Figure 1). Nutrients moved via crops to urban centers are hardly ever recycled and commonly end up into streams, lakes, or the ocean [4].

Increasing agricultural production in SSA is likely going to be the result of intensification and area expansion [5]. Intensification of agricultural production is a must in the more densely populated areas in order to feed the rapidly growing and urbanizing population. The recent call for an African Green Revolution [6] is an example of the urgency to remediate the current situation. For areas that contain valuable natural ecosystems, such as the primary forest in the Congo basin, intensification of agriculture is one of the pillars of the strategy to conserve forest [7]. As for the Sahelo-Saharan region, an extensive livestockbased system is likely the only option without degrading the resource base. Other areas in SSA indeed are sparsely populated, contain less valuable or diverse natural ecosystems, and could thus be opened up for …