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Keywords:

  • soil organic matter;
  • soil degradation;
  • global warming;
  • soil restoration;
  • agroforestry;
  • farming systems;
  • ecoregions;
  • sub-Saharan Africa;
  • carbon sequestration in soil

Abstract

Restoration of degraded soils is a development strategy to reduce desertification, soil erosion and environmental degradation, and alleviate chronic food shortages with great potential in sub-Saharan Africa (SSA). Further, it has the potential to provide terrestrial sinks of carbon (C) and reduce the rate of enrichment of atmospheric CO2. Soil organic carbon (SOC) contents decrease by 0 to 63 per cent following deforestation. There exists a high potential for increasing SOC through establishment of natural or improved fallow systems (agroforestry) with attainable rates of C sequestration in the range of 0·1 to 5·3 Mg C ha−1 yr−1. Biomass burning significantly reduces SOC in the upper few centimeters of soil, but has little impact below 10 to 20 cm depth. The timing of burning is also important, and periods with large amounts of biomass available generally have the largest losses of SOC. In cultivated areas, the addition of manure in combination with crop residues and no-till show similar rates of attainable C sequestration (0 to 0·36 Mg C ha−1 yr−1). Attainable rates of SOC sequestration on permanent cropland in SSA under improved cultivation systems (e.g. no-till) range from 0·2 to 1·5 Tg C yr−1, while attainable rates under fallow systems are 0·4 to 18·5 Tg C yr−1. Fallow systems generally have the highest potential for SOC sequestration in SSA with rates up to 28·5 Tg C yr−1. Copyright © 2005 John Wiley & Sons, Ltd.