Nitrogen fertilization is considered as an important source of atmospheric N2O emission. A seven site-year on-farm field experiment was conducted at Ottawa and Guelph, ON and Saint-Valentin, QC, Canada to characterize the affect of the amount and timing of N fertilizer on N2O emission in corn (Zea mays L.) production. Using the static chamber method, gas samples were collected for 28-days after preplant and 28-days after sidedress fertilization at the seven site-year, resulting in 14 monitoring periods. For both methods of fertilization, peak N2O flux and cumulative emission increased with the amount of N applied, with rates ranging from 30 to 900 mu g N m(-2) h(-1). Depending on N amount and time of application, cumulative emission varied from 0.05 to 2.42 kg N ha(-1), equivalent to 0.03% to 1.45% of the N fertilizer applied. Differences in N2O emission peaks among fertilizer treatments were clearly separated in 13 out of 14 monitoring periods. Total N2O emissions may have been underestimated compared with annual monitoring in 10 out of the 49 cases because the monitoring period ended before N2O efflux returned to the baseline level. The flux of N2O was negligible when soil mineral N in the 0-15 cm layer was 15 degrees C was likely the driving force responsible for the higher levels of N2O found for sidedress than preplant application methods. However, caution must be taken when interpreting these later results as preplant fertilization may have continuously stimulated N2O emissions after the 28-days monitoring period, especially in situations where N2O effluxes have not fallen back to their baseline levels. Increasing fertilizer rates from 90 to 150 kg N ha(-1) resulted in slight increases in yields, but doubled cumulative N2O emissions.
