Simulation of spatial and temporal dynamics of soil organic carbon reserve in Romania

The present study performs a simulation of soil organic carbon (SOC) dynamics in Romania by coupling an evolution model of organic carbon with an erosional model. The simulation starts from the current SOC reserve, computed for the first 20 cm of soil, based on organic carbon content and bulk density, the latter being estimated through a pedotransfer function. The evolution model of SOC takes into account the annual accumulation of organic residues, the active and stable organic carbon contents, the humification and mineralization rates. The annual accumulation of organic residues is estimated from crop type for the arable land and from Corine Land Cover land use / cover types for the rest of the territory. The humification rate of organic residues is expressed through the izohumic coefficient, which depends on the land use/cover type. The mineralization rate of the active organic carbon content depends on climate factors (temperature) and granulometry (clay content). The application of the SOC evolution model produces an estimation of SOC accumulation under automorphic conditions. On the other hand, erosional processes determine soil loss and implicitly soil carbon loss. To account for this impact, we used an erosion model based on the universal soil loss equation, which was adapted and validated for the Romanian territory. Assuming the annual erosion rates are constant, our 50 years simulation show that important areas of the country, situated in the plateau and hilly regions, are experiencing a regressive dynamic of SOC. Under climate change scenarios, the temperature increase may enhance the mineralization of active SOC, leading to a more intense depletion of soil fertility.