McCarty, Gregory (USDA-AR, Building 007, Rm 202, BARC-WestBeltsville, MD, 20705; Phone: 301-504-7401; Fax: 301-504-5048; Email: mccartyg@ba.ars.usda.gov)

 

Modeling Soil Carbon Sequestration in Agricultural Lands of Mali, Africa

 

G.W. McCarty *, P.C. Doraiswamy, E.R. Hunt, R.S.Yost, M. Doumbia, A.J. Franzluebbers

 

Agriculture in sub-Saharan Africa is a low-input low-output system for subsistence. Some of these areas are becoming less able to feed the people, because of land degradation and erosion. The aims of this study are to characterize the potential for increasing levels of soil carbon for improving soil quality and carbon sequestration. A combination of high- and low- resolution imagery were used to develop a landuse classification for an area of 64 km2 near Omarobougou, Mali. Field sizes were generally small (less than 1 ha), and the primary cultivation systems are conventional tillage and ridge tillage. Based on land-use classification, climate variables, soil texture, in-situ soil carbon concentrations, and crop growth characteristics, the EPIC-Century model was used to map the current and projected amounts of soil carbon sequestered for the region. The range of yields for maize for the past 6 years (1997-2002) was between 2-6 Mg/ha, millet yields ranged between 0.6-1.1 Mg/ha, and sorghum yields ranged between 26 Mg/ha. Year-to-year variations can be attributed to primarily rainfall and availability of fertilizer. Under continuous conventional cultivation with minimal fertilization and no residue management, the soil top layer was continuously lost due to erosion, losing between 1.1 to 1.7 Mg C/ha over 25 years. The model projections suggest that soil erosion is controlled and that soil carbon sequestration is enhanced with a ridge tillage system, because of increased water infiltration which increases production. The combination of modeling with the land use classification was used to calculate that between 40 to 104 Mg C /year may be sequestered for the study area with ridge tillage, increased application of fertilizers, and improved residue management.