Soil organic carbon in agricultural systems of six countries in East Africa – a literature review of status and carbon sequestration potential
Sara Namirembe, Kristin Piikki, Rolf Sommer, Mats Söderström, Bezaye Tessema, Sylvia S. Nyawira
Abstract
Cropland soils are considered to have the potential to sequester atmospheric CO2 through agronomic best management practices (BMPs). To estimate this potential in East Africa, the authors reviewed 69 published studies from Ethiopia, Kenya, Rwanda, Tanzania, Uganda, and Burundi assessing the effect of land use conversion from native vegetation to cropland on soil organic carbon (SOC) and the extent to which carbon sequestration is feasible through BMPs. Reported losses of SOC in the top 30 cm of the soil profile in short (<10 years), medium (10–25 years), and long (>25 years) term were 6.7 ± 6.0, 13.0 ± 9.2, and 2.8 ± 1.0 t C ha–1 year–1, respectively, for forest-to-cropland; and 16.0, 2.1 ± 2.2 and 0.3 ± 0.8 t C ha–1 year–1 respectively, for woodland-to-cropland conversion. Duration to steady-state SOC was 21–38 years for forest-to-cropland conversion. Short-term SOC sequestration (t C ha–1 year–1) in the 0–30 cm layer as a result of BMPs was 19.7 ± 3.9 from crop residues, 14.8 ± 8.7 from farmyard manure, 3.5 ± 4.5 from inorganic fertilizers, 2.7 from agroforestry, and 2.5 from improved fallow. However, the studies reviewed were mostly short-term and concentrated to a few locations. Future research should address these gaps.