SOM dynamics and erosion in an agricultural test field of the Clear Creek, IA watershed

Abstract. To date, few studies have examined in detail the role of spatial variabilities of erosion on Soil Organic Matter (SOM). More specifically, the role of deposition is still poorly understood. The nature of the research is novel because it combines dynamic model simulations using the Water Erosion Prediction Project (WEPP) and CENTURY SOM dynamics model to evaluate soil and SOM loss in an agricultural test field of the Clear Creek, IA watershed. In addition, numerical simulations were coupled with limited field investigations calibrating and verifying WEPP and CENTURY. The main task of this study was to evaluate changes in SOM dynamics in a field using CENTURY and accounting for the interdependence of historical and current management practices, erosion (i.e., soil loss and deposition), and decomposition. Simulations were conducted under three different erosion scenarios determined using WEPP to demonstrate the importance of including deposition in studies of SOM dynamics: (1) assuming no erosion, (2) using an average erosion rate for the whole field, and (3) dividing the field into an erosional upland and depositional floodplain. The total SOM concentrations produced by the segmented field simulation agreed best with the measured field values. Simulated SOM concentrations values for the upland were 13% lower and values for the floodplain were 16% higher than measured field values. The results of this investigation compare well with the simulation results of other studies in terms of the effects of deposition on SOM distributions and that more detailed erosion values lead to better performance of the model. Deposition decreased SOM loss from the field by accounting for sequestration of carbon.