Response of soil organic carbon to land-use change in central Brazil: a large-scale comparison of Ferralsols and Acrisols

The southeastern part of the Amazon region is one of the largest agricultural frontiers in the world, leading to extensive land-use change. This paper provides evidence for the impacts of land-use change on soil organic carbon (OC) stocks along a large scale for Ferralsols and Acrisols including subsoil. We took soil samples to 100 cm depth for native vegetation, pasture and crop-field along a 1000 km agricultural transect in central Brazil to determine OC stocks and, by using a stable isotope approach, losses of forest-derived OC. At the scale of individual plots, soil OC stocks indicate a highly heterogeneous response to land-use change (e.g. in Ferralsols in 0-30 cm from -45 % to +57 % Mg OC ha(-1) after conversion to pasture), but relatively minor responses when considering the complete transect (i.e. no significant OC changes for similar land-use type). Acrisols evidenced a slower decline of forest-derived OC and simultaneously a faster accumulation of pasture-derived OC than Ferralsols. Surprisingly, the impact of land-use change was more pronounced in the subsoil. Our results emphasize the role of subsoils on carbon cycling which has been previously underestimated, but may also raise doubts whether OC stocks in soil is an appropriate parameter to assess the impacts of land-use conversion on climate change.