Dynamics of carbon loss from an Arenosol by a forest to vineyard land use change on a centennial scale

Few studies have focused on Arenosols with regard to soil carbon dynamics despite the fact that they represent 7 % of the world's soils and are present in key areas where food security is a major issue (e.g., in Sahelian regions). As for other soil types, land use changes (from forest or grassland to cropland) lead to a loss of substantial soil organic carbon (SOC) stocks and have a lasting impact on the SOC turnover. Here we quantified long-term variations in carbon stocks and their dynamics in a 80 cm deep Mediterranean Arenosol that had undergone a forest-to-vineyard land use change over a 100 years ago. Paired sites of adjacent plots combined with carbon and nitrogen quantification and natural radiocarbon (C-14) abundance analyses revealed a C stock of 53 t ha(-1) in the 0-30 cm forest soil horizon, which was reduced to 3 t ha(-1) after long-term grape cultivation. Total organic carbon in the vineyard was dramatically low, with around 1 g C kg(-1), and there was no vertical gradient as a function of depth. C-14 showed that deep plowing (50 cm) in the vineyard plot redistributed the remaining carbon both vertically and horizontally. This remaining carbon was old (compared to that of the forest), which had a C : N ratio characteristic of microbial organic matter and was probably stabilized within organomineral associations. Despite the drastic degradation of the organic matter (OM) pool in this Arenosol, this soil would have a high carbon storage potential if agricultural practices, such as grassing or organic amendment applications, were to be implemented within the framework of the 4 per 1000 initiative.