Soil carbon losses in conventional farming systems due to land-use change in the Brazilian semi-arid region

Conventional farming systems reduce soil organic carbon (SOC) stocks in tropical regions, predisposing these soils to emit CO2 to the atmosphere. However, studies conducted worldwide have shown that the magnitude of these losses depends on the management practices adopted as well as climate and soil conditions; thus, accurately quantifying these SOC changes can be a major challenge. In this regard, the aim of this study was to derive specific SOC stock change factors for conventional farming systems in the semi-arid region of Brazil and to evaluate the impacts caused by the conventional systems of annual crops throughout time and soil profile on SOC stocks in this region. A total of 66 pairs of comparisons were used, and datasets were analyzed through a mixed linear model. Conventional systems with annual crops reduced the SOC stocks by 17, 13 and 4% for the 0-30, 0-50 and 0-100 cm soil layers, respectively, and for the period of 20 years of land use change. The SOC losses increased with the crop period, since the land-use change factors derived for 40 years showed a decrease of 26, 22 and 13% for the 0-30, 0-50, and 0-100 cm soil layers, respectively, when compared to the SOC stocks in native vegetation.