The role of field studies in landscape-scale applications of process models: an example of soil redistribution and soil organic carbon modeling using CENTURY

Field studies on soil properties and processes in southern Saskatchewan have clearly indicated the need to account for both lateral and vertical transfers of components in the landscape for a better understanding of soil dynamics at a given point. Extrapolation of these studies requires greater integration of the site-specific field results with the current generation of process models. In this paper, we use the results of a field study to assess the ability of the CENTURY model to describe the influence of soil redistribution on soil organic carbon (SOC) dynamics. After modifying the erosion input of CENTURY to account for soil deposition, the results from CENTURY were compared to measured SOC levels from a chronosequential study of cultivation effects on SOC levels in southern Saskatchewan. CENTURY closely simulated the effects of soil loss on SOC levels in landform segments with dominantly convex profile (i.e., downslope) curvature. CENTURY estimates of SOC changes for landform segments experiencing soil gain are less comparable to the field results; it overestimated SOC loss after 80 years by 16 Mg ha⁻¹ for depressional complexes and 10 Mg ha⁻¹ for footslope complexes. This leads to a 14% difference in total SOC loss on a landscape-weighted basis (estimated loss based on field data of 36 Mg ha⁻¹ versus a CENTURY-simulated loss of 41 Mg ha⁻¹).