Carbon sequestration in soils is an action which could both improve agricultural yields and offset greenhouse gases emissions of anthropogenic source. Two experiments in tropical sub-humid zone of 21years in Gagnoa, Ivory Coast; and 23 years in Aplahouhé, Benin, have shown that significant and regular contributions of compost in Gagnoa and of buried crop residues in Aplahoué strongly increased maize yields compared to plots without organic amendments. This performance difference was greater when no mineral fertilization was made. Meanwhile, in Gagnoa as in Aplahouhé, soil carbon stocks on plots with and without organic amendments have drastically decreased in the 0-20 cm surface horizon during the experiment: of 60 and 75% in Gagnoa and Aplahouhé respectively. Plots which have annually been supplied with organic amendments of 10 t / ha of dry compost materials in Gagnoa and crop residues in Aplahouhé for more than 20 years showed a surplus of carbon stock in their soil, of not more than 6 t / ha compared to plots without contributions from both sites. The sharp decline in carbon stocks by crop setting observed in these experiments confirms the hypothesis of physical un-protection of soil carbon by destruction of soil macro-aggregates following cultivation. The increases in yield through organic inputs might be due to a mineral effect and to an increase of the biological soil fertility following the strong mineralization of organic matter. These results confirm the interest of organic amendments to maintain high yields in tropical areas, but indicate their low capacity for storing a large enough amount of carbon for a real mitigation impact.