Sustainable intensification of agriculture in sub-Saharan Africa: first things first

We both belong to a generation of soils scientists and agronomists who have spent or are spending their career trying to develop and scale better soil and crop management solutions for smallholder farmers in the tropics.We have witnessed some successes in this, but also many disappointments.However, the work of the first author (BV) has primarily been in sub-Saharan Africa (SSA), while much of the work of the second author (AD) has been in Asia.We both believe that there is great urgency to accelerate crop production in Africa, the region with the greatest challenges for food and nutritional security and socioeconomic prosperity.We believe that what SSA needs most now is an agronomic revolution.This paper presents our personal reflections on what should come first, knowing very well that the challenge is complex, requiring well-tailored, longer-term plans for numerous interventions driven by many different actors.Naturally, such plans for the sustainable development of agriculture differ widely and we are not able to cover all aspects of this here.Although SSA clearly has its own biophysical and socioeconomic characteristics, we believe that it can benefit greatly from experiences of other regions, including making sure that first things come first, thereby avoiding earlier mistakes. The African challenge is not so differentSub-Saharan Africa is facing challenges and opportunities that are not fundamentally different from what other world regions have experienced at different stages of their development.We know that there is a large food demand-supply gap that may even widen in the coming decades as a result of rapid population and income growth [1] .We also know that although there are large crop yield gaps that must be reduced, this alone will not be sufficient to feed Africa.Consequently, similarly to what happened in other regions of the world, agricultural development in SSA must also include cropland expansion, increasing cropping intensity on existing land and expansion of irrigation [2] , but doing that in a socially and environmentally sustainable manner.It is also clear that there are massive nutrient gaps that must be overcome in SSA [3] .Finally, as in other regions, SSA is also undergoing a structural transformation of its economy and farming, which is likely to accelerate in the coming years [4,5] .The key outcomes of this typically include: growing ruralurban market integration, a dramatic decline of the share of population working in agriculture, more aggregation of farms and/or services and value chains, increasing input use, higher labor productivity and a greater need for mechanization.Countries in SSA are at different stages of development and structural transformation, and there is also huge variation within countries in the use of inputs such as seed, fertilizers and other agrochemicals, machinery and irrigation [6] .The basic economic and social forces driving the structural transformation of farming in SSA will largely also drive the solutions that need to be found for sustainable