A field lysimeter study was conducted to determine the sources of N₂O emitted following the application of dairy cow urine and urea fertiliser labelled with ¹⁵N, with and without a nitrification inhibitor, dicyandiamide (DCD). The results show that the application of cow urine at 1000 kg N/ha significantly increased N₂O emissions above that from urea applied alone at 25 kg N/ha. The application of urine seemed to have a priming effect, increasing N₂O emissions from the soil N pool. Treating the soil with DCD significantly (P < 0.05) decreased N₂O emissions from the urine-applied treatment by 72%. The percentage of N₂O-N derived from the applied N was 53.1% in the urine-applied treatment and this was reduced to 29.9% when DCD was applied. On average, about 43% of the N₂O emitted in the urine-applied treatments was from nitrification. The application of DCD did not have a major effect on the relative contributions of nitrification and denitrification to N₂O emissions in the urine treatments. This indicates that the DCD nitrification inhibitor decreased the contributions to N₂O emissions from both nitrification and denitrification.