Land pressure and soil nutrient depletion in sub-Saharan Africa

Soil nutrient depletion and other forms of soil degradation threaten future soil productivity, especially in sub-Saharan Africa (SSA). Even under optimistic assumptions, data from SSA show that 8–12 years of fallow are needed to replenish the nitrogen pool after 2–3 years of cropping. This implies that for sustainable soil management at the current level of fertilizer and manure inputs, it would only be possible to cultivate annually about 20% of the arable land. This situation rarely exists today in SSA where, through population pressure, the average percentage of land cultivated is about 60%. The data illustrate that soil conservation and improved nutrient management are crucial but can only reduce the speed of nutrient depletion. Availability and efficient use of farm external inputs will be required to make a broad impact. Data from 37 countries in SSA show a significant relationship between nutrient depletion and land pressure indicators and thus illustrate the unsustainable population–agriculture–environment nexus on the continent. Nutrient depletion accounts for about 7% of the agricultural share of the average gross domestic product of SSA, indicating nutrient mining is a significant factor in current economic development.