Nitrous oxide (N₂O) is a greenhouse gas involved in global warming and stratospheric ozone depletion. Soils, and particularly agricultural soils, are a dominant source of N₂O. In soils, the production of N₂O results mainly from the aerobic and anaerobic processes of nitrification and denitrification respectively. Identifying the mechanisms responsible for N₂O emission should help to define methods for its mitigation. The relative contribution of nitrification and denitrification to the formation of N₂O varies considerably, and depends on environmental conditions. Likewise, the relationship between nitrification rates, N₂O production and soil conditions is not yet well known. Hence, process-oriented models of N₂O emissions by soils generally assume N₂O produced through nitrification to be a constant part of the nitrification rate. The aim of this work was to investigate the relative contribution of nitrification and denitrification to N₂O emission, and then evaluate the portion of N₂O emitted during the nitrification process using ¹⁵N isotope tracers. Relative contributions of both processes to N₂O emissions were estimated, on an agricultural soil (Gleyic luvisol), using ¹⁵N isotope tracers (¹⁵NH₄⁺ or ¹⁵NO₃^-), for a ten-day batch experiment. Under unsaturated and saturated conditions, both processes were significantly involved in N₂O production. Under unsaturated conditions, 60% of N-N₂O came from nitrification, while denitrification contributed around 85-90% under saturated conditions. Estimated nitrification rates were not significantly different whatever the soil moisture content, whereas the proportion of nitrified N emitted as N₂O increased strongly from 0.13% to 2.32%. In coherence with previous studies, we interpreted this high value as resulting from the decrease in O₂ availability through the increase in soil moisture content. It thus appears that, under limiting aeration conditions, some values for N₂O emissions through nitrification could be underestimated. These different results suggest the introduction, in process-oriented models of N₂O emissions, of a varying factor of N-N₂O induced by nitrification. This factor should be linked to soil environmental conditions.