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Conversion of native ecosystems to agro-ecosystems influences the amount, quality and turnover of soil organic carbon (SOC). As most agro-ecosystems are not in a steady state in terms of the content of SOC, the time scale and feedback mechanisms of changes in SOC are highly relevant for predicting future soil fertility and potential rates of soil carbon losses or sequestration. This paper focuses on changes in land use linked to measured changes in the distribution of total stocks of SOC and the δ¹³C signature in the upper 0.5 m of cultivated soils in the semi-arid parts of Tanzania. Based on documented land use changes since 1950s using remote sensing data, 12 sampling sites along two transects were selected to represent semi-natural/natural savannah and maize fields cultivated for up to five decades. Comparisons between sites representing a chronosequence of well-drained soils showed that soils …