Simulating Soil Carbon Dynamics, Erosion and Tillage with EPIC

Carbon sequestration in soil has emerged as a technology with significant potential to help stabilize atmospheric concentrations of greenhouse gases at non-threatening levels. Methods are thus needed to evaluate and recommend soil carbon sequestration practices based on their effects on carbon dynamics and environmental quality. There is scientific and practical consensus that simulation models will be integral to these methods. EPIC (Erosion Productivity Impact Calculator) is a widely used and tested model for simulating agroecosystem processes; it can handle multiple crops and has dynamic treatment of tillage, wind and water erosion, runoff, soil density, and leaching processes. In order to improve the simulation of soil carbon dynamics as affected by erosion and tillage, here we describe changes made to the EPIC model following concepts used in the Century model. The C and N dynamics captured from Century now interact directly with the soil moisture, temperature, erosion, tillage, soil density, leaching, and translocation functions of EPIC. Equations were also added to describe the role soil texture plays in soil organic matter stabilization. Differences in N mineralization and immobilization between the two models are explained. In the newly modified EPIC, leaching moves materials from surface litter to subsurface layers. In contrast to Century, the surface litter in EPIC has a slow but no passive compartment. Lignin concentration in EPIC is modeled as a sigmoidal function of plant age. Model comparisons against selected long-term data sets are presented and discussed. 1 Paper presented at the First National Conference on Carbon Sequestration organized by the U.S. Department of Energy— National Energy Technology Laboratory and held at the Renaissance Washington DC Hotel in Washington, DC, on May 14–17, 2001.