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Agricultural soils emit nitrous oxide (N2O), a potent greenhouse gas. Predicting and mitigating N2O emissions is not easy. To derive national coefficients for N2O emissions from soil, we collated over 400 treatment evaluations (measurements) of N2O fluxes from farming systems in various ecoregions across Canada. A simple linear coefficient for fertilizer-induced emission of N2O in non-manured soils (1.18% of N applied) was comparable to that used by the Intergovernmental Panel on Climate Change (IPCC) (1.25% of N applied). Emissions were correlated to soil and crop management practices (manure addition, N fertilizer addition and inclusion of legumes in the rotation) as well as to annual precipitation. The effect of tillage on emissions was inconsistent, varying among experiments and even within experiments from year to year. In humid regions (e.g., Eastern Canada) no-tillage tended to enhance N2O emissions; in arid regions (e.g., Western Prairies) no-tillage sometimes reduced emissions. The variability of N2O fluxes shows that we cannot yet always distinguish between potential mitigation practices with small (e.g., < 10%) differences in emission. Our analysis also emphasizes the need for developing consistent experimental approaches (e.g., 'control' treatments) and methodologies (i.e. measurement period lengths) for estimating N2O emissions.