To improve soil health and increase crop yields, organic matter is commenly added to arable soils. Studying the effect of different organic resources on soil organic carbon sequestration in four long-term field trials in Kenya, we found that only a small portion (< 7 %) of added organic carbon was stabilised, which was only observed in the top 15 cm of the soil. These results underline the challenges associated with increasing the organic carbon content of tropical arable soils.