Agroforestry innovations for soil fertility management in sub-Saharan Africa: prospects and challenges ahead

Improving soil fertility is a key entry point for achieving food security, reducing poverty and preserving the environment for smallholder farms in sub-Saharan Africa. Given the high cost of inorganic fertiliz - ers, an integrated approach that combines promising agroforestry technologies – particularly improved fallows and biomass transfer – with locally available and reactive phosphate rock – such as the Min - jingu of northern Tanzania – is described in this chapter. Leguminous tree fallows of several species can accumulate significant amounts of nitrogen in their leaves in the short duration (from 6 months to 2 years). Incorporating these leaves into the soil before planting can increase crop yields several-fold. Improved fallows can also contribute to the control of weeds (including Striga hermontheca ) and pro - vide wood for energy and for staking climbing crops. Some of the species also have fodder value that can improve manure quantity and quality. For biomass transfer, use of Tithonia diversifolia is the most promising because of its high nutrient content and rapid rates of decomposition. This plant is now being used more widely for high-value crops such as vegetables. To facilitate the scaling up of these fertility options, future research and development needs to address recommended application rates, impacts at both farm and landscape levels, and the method by which high-value trees, crops and livestock can be intensively farmed to provide a natural progression out of poverty.

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