Atmosphere composition and N2O emissions in soils of contrasting textures fertilized with anhydrous ammonia

Nitrous oxide production and emission in agricultural soils are often influenced by soil physical properties and mineral N content. An experiment was initiated on a commercial farm located in the St. Lawrence Lowlands to measure the effects of recommended (150 kg N ha⁻¹) and excessive (250 kg N ha⁻¹) rates of anhydrous ammonia on atmospheric composition (O₂, CO₂, CH₄ and N₂O) and N₂O emissions in soils of contrasting textures (sandy loam, clay loam and clay) cropped to corn. N₂O emissions and soil temperature, water content and atmospheric composition were measured from post-harvest tillage to the first snowfall during the first year (2000), and from spring thaw to mid-July during the following 2 yr. Episodes of high N₂O concentrations and surface emissions coincided with periods of high soil water content shortly following rainfall events when soil O₂ concentrations were lowest. The convergence of indicators of restricted soil aeration at the time of highest N₂O production suggested that denitrification was a major contributor to N₂O emissions even in soils receiving an NH₄-based fertilizer. Soil texture had a significant influence on soil N₂O concentration and emission rates on several sampling dates. However, the effect was relatively small and it was not consistent, likely because of complex interactions between soil physical properties and N₂O production, consumption and diffusion processes. Nitrous oxide emissions during the study were not limited by soil N availability as indicated by similar fluxes at recommended and excessive rates of anhydrous ammonia. Finally, greater N₂O emissions in 2001 than in 2002 stress the importance of multiyear studies to evaluate the effect of annual weather conditions on soil N₂O dynamics. Key words: Greenhouse gasses, denitrification