We have directly measured nitrous oxide flux rates from well aerated agricultural soil (Fox sandy loam and Harrow fine sandy loam) located in Essex County, southwestern Ontario. Evidence was obtained showing that the release of N2O was strongly related to the rate of fertilizer application during the interval 6 to 43 days after soil treatment. Emission rates on NH4NO3 fertilized plots planted to corn were in the range 7.04¿10-4 to 2.64¿10-2 kg N ha-1 day-1; rates on more heavily fertilized plots planted to burley tobacco were generally higher in the range 1.45¿10-3 to 3.20¿10-2 kg N ha-1 day-1. We briefly discuss our observations in terms of loss of fertilizer nitrogen as N2O and the impact of increasing fertilizer addition on the extent of N2O evolution.