Drainage and cultivation of organic soils often result in large nitrous oxide (N2O) emissions. The objective of this study was to assess the impacts of nitrogen (N) fertilizer on N2O emissions from a cultivated organic soil located south of Montreal, QC, Canada, drained in 1930 and used since then for vegetable production. Fluxes of N2O were measured weekly from May 2004 to November 2005 when snow cover was absent in irrigated and non-irrigated plots receiving 0, 100 or 150 kg N ha(-1) as NH4NO3. Soil mineral N content, gas concentrations, temperature, water table height and water content were also measured to help explain variations in N2O emissions. Annual emissions during the experiment were large, ranging from 3.6 to 40.2 kg N2O-N ha(-1) year(-1). The N2O emissions were decreased by N fertilizer addition in the non-irrigated site but not in the irrigated site. The absence of a positive influence of soil mineral N content on N2O emissions was probably in part because up to 571 kg N ha(-1) were mineralized during the snow-free season. Emissions of N2O were positively correlated to soil CO2 emissions and to variables associated with the extent of soil aeration such as soil oxygen concentration, precipitation and soil water table height, thereby indicating that soil moisture/aeration and carbon bioavailability were the main controls of N2O emission. The large N2O emissions observed in this study indicate that drained cultivated organic soils in eastern Canada have a potential for N2O-N losses similar to, or greater than, organic soils located in northern Europe.
