Updates in the development of methodologies for estimating CO2 and N2O emission factors using process-based models (DAYCENT, DNDC, ecosys) will be presented under a selected range of agricultural practices (rotations, tillage, fertilizer) in different regions of Canada. The methodology will be supported by testing with measurements of emissions taken under well-specified field conditions, and on a range of field results recorded under diverse field conditions. These emission factors will allow users to estimate the GHG implications of changing rotations (e.g. reducing fallow, including legumes and perennials), rates and methods of fertilizer application (e.g. incorporation depth, banding vs. broadcast), and tillage (zero, minimum and conventional) on different soil types under different climates. These factors are being developed as part of Canada's national inventory of GHG emissions in the agricultural sector.