Biophysical potential for soil carbon sequestration in agricultural systems of the Old Peanut Basin of Senegal

Carbon sequestration in soil organic matter is increasingly advocated as a possible win-win strategy in the rehabilitation of degrading dryland agro-ecosystems because it simultaneously contributes to the reduction of global atmospheric greenhouse gas concentrations while enhancing local land productivity. A study was conducted in Senegal's Old Peanut Basin to assess current carbon stocks and to examine management options for their increase. Average soil and woody biomass carbon contents were 11.3 and 6.3 t carbon (C) ha(-1), respectively. CENTURY, a biogeochemical model, was used to simulate soil and biomass carbon over a period of 25 and 50 years under a series of land use and management options. These simulated practices resulted in C dynamics ranging from -0.13 t C ha(-1) yr(-1) from a worst-case millet-sorghum rotation to +0.43 t C ha(-1) yr(-1) on intensively managed agricultural fields. Agroforestry simulations involving Faidherbia albida (Del.) Chev. and Leucaena leucocephala (Lam.) deWit. also resulted in promising carbon gain (+0.22 and +0.12 t C ha(-1) yr(-1), respectively), suggesting that improving agricultural practices is key to enhancing food production and mitigating climate change. Results from a sensitivity analysis suggest that woody biomass carbon is more sensitive to long-term changes in precipitation and temperature than soil carbon. Other management strategies likely to result in lower rates of soil carbon sequestration, including short-term improved fallows, should also be considered viable opportunities because promoting too narrow a set of 'best management practices' risks weakening local adaptability and opportunistic management regimes, both of which are crucial elements in small-scale farming systems in drylands. (C) 2004 Elsevier Ltd. All rights reserved.