Technical Abstract: DayCent is a biogeochemical model of intermediate complexity used to simulate carbon, nutrient, and greenhouse gas fluxes for crop, grassland, forest, and savanna ecosystems. Model inputs include: soil texture and hydraulic properties, current and historical land use, vegetation cover, daily maximum and minimum temperature, and daily precipitation. The latest version allows daily (instead of monthly) scheduling of management events and calculates plant production at a daily (instead of weekly) time step. The ability of the model to simulate crop yields, soil carbon changes, N2O emissions, and NO3 leaching was tested using data from different irrigated and rainfed cropping systems. DayCent has recently been applied to calculate N2O emissions from cropped and grazed soils for the U.S. National Greenhouse Gas Inventory and to perform life cycle analysis of greenhouse gas fluxes for biofuel cropping systems. Future versions of the model will more completely represent the range of greenhouse gas mitigation options available with current technologies.