Where do we stand 20 years after the assessment of soil nutrient balances in sub-saharan Africa

To feed 9 billion people in 2050, recent estimates indicate that global food production will have to increase by 70% [FAO 2009]. Food security can be realized by expanding the cultivated area and by increasing production per unit land, labor, or capital. Further down the production-consumption chain, increasing ef…ciency and recycling (including postharvest and waste management) and dietary change also are important. To increase agricultural production, area expansion is still possible, mainly in the range of Ukraine-Russia-Kazakhstan, in sub-Saharan Africa (SSA), and in Latin America, but it will negatively affect the services provided by natural ecosystems. The recent agricultural area expansions in Latin America (soybean for savannah and Amazon forest) and Southeast Asia (oil palm for rainforest and peat lands) clearly show the dilemmas: a booming international market for soy and palm oil and for soy meal as animal feed [Smaling et al. 2008], go at the expense of natural vegetation, plant and animal biodiversity, climatic stability, and above-and below-ground carbon (C) stocks. Hence, raising productivity is the main feasible option on the upstream part of the food security chain. This is still possible in most agricultural systems, but the immediate large increases in cereal production of the Green Revolution will not be repeated easily. As Conway [1997] expressed, “What is needed is a doubly green revolution that raises yields while reducing environmental impact.”