N 2 O emissions from an irrigated and non‐irrigated organic soil in eastern Canada as influenced by N fertilizer addition

Drainage and cultivation of organic soils often result in large nitrous oxide (N 2 O) emissions. The objective of this study was to assess the impacts of nitrogen (N) fertilizer on N 2 O emissions from a cultivated organic soil located south of Montréal, QC, Canada, drained in 1930 and used since then for vegetable production. Fluxes of N 2 O 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 NH 4 NO 3 . Soil mineral N content, gas concentrations, temperature, water table height and water content were also measured to help explain variations in N 2 O emissions. Annual emissions during the experiment were large, ranging from 3.6 to 40.2 kg N 2 O‐N ha −1 year −1 . The N 2 O 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 N 2 O emissions was probably in part because up to 571 kg N ha −1 were mineralized during the snow‐free season. Emissions of N 2 O were positively correlated to soil CO 2 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 N 2 O emission. The large N 2 O emissions observed in this study indicate that drained cultivated organic soils in eastern Canada have a potential for N 2 O‐N losses similar to, or greater than, organic soils located in northern Europe.