The DayCent biogeochemical model was parameterized to simulate miscanthus and switchgrass using data from field plots in Illinois, Pennsylvania, Nebraska, and Iowa. Correlation coefficients (r²) for observed vs. simulated biomass yields were 0.54 for miscanthus and 0.55 for switchgrass. When yields from these perennials were regressed with previously tested corn grain yields, the overall r² value was 0.88. Changes in soil carbon (r² = 0.65) and N₂O emissions (r² = 0.95) for these systems were also represented reasonably well by the model. County level simulations were conducted for land currently used for corn cropping in the Mississippi basin. If cellulosic feedstocks were planted on land that is currently used for corn ethanol production in the central US, ethanol would increase  by about 80%, soil greenhouse gas emissions would decrease by 30 to 400%, and NO₃ leaching would decrease by 15 to 20%.