Sorghum, millets (pearl and finger millet) and grain legumes (chickpea, common bean, cowpea, lentils, pigeon pea and soybean), collectively referred to as GLDC under the CGIAR research program on Grain Legumes and Dryland Cereals, are commonly grown, eaten and traded by small holder farmers in Africa and South Asia. These crops contribute to food and nutritional security, environmental sustainability, and economic growth in the region. However, their possible contribution to carbon sequestration through biomass production and accumulation of soil organic carbon (SOC) is not known. To find out more about their contribution, and how to increase SOC, this study reviewed the evidence of carbon sequestration in farming systems that integrate GLDC in Africa and South Asia. A total of 437 publications reporting SOC and its proxies across 32 countries in Africa (N=250 studies) and South Asia (N=187) were identified as sources of evidence for carbon sequestration. Among these, 179 publications provided appropriate control groups for evaluating changes in aboveground carbon when GLDC were integrated under intercrop (n=38), crop rotation (n=8) or agroforestry (n=13), or when improved varieties of GLDC were compared with local varieties (n=14). A further 81 publications compared SOC content at the start and the end of the experiment while 43 publications compared SOC between farms growing GLDC and those which did not. Aboveground carbon of GLDC was found to be 1.51±0.05 Mg/ha in Africa and 2.29±0.10 Mg/ha in South Asia. Absolute SOC concentration in the topsoil (0-30 cm) was 0.96±0.06% in Africa and 0.58±0.04 in South Asia. It was observed that GLDC produced more aboveground carbon and significantly increased SOC when grown as intercrops and in crop rotations. The increase, however, depended on the species and whether the crop was a legume or a cereal. The largest amount of aboveground carbon (>2 Mg/ha) was found in cereals (and pigeon pea) while the largest increase in SOC was found in farming systems that included legumes. Aboveground carbon of improved varieties of GLDC was lower compared to local varieties. Soils which had low initial (32%) showed the greatest potential for carbon sequestration when GLDC were grown. Among the GLDC crops, pigeon pea which is a perennial grain legume showed the highest biomass production and carbon sequestration in the soil when integrated into farming systems in Africa and South Asia. Findings from this study underscore the importance of aboveground residues in regulating the addition of carbon to the soil, and the role of legumes in the enhancement of SOC
