The ways in which agricultural soils are managed influence the production and emission of nitrous oxide (N2O). A field study was undertaken in 2003, 2004, and 2005 to quantify and evaluate N2O emission from tilled and no-till soils under corn (Zea mays L.) and soybeans (Glycine max L. Merr.) in Ontario. Overall, N2O emission was lowest in 2003, the driest and coolest of the 3 yr. In 2004, the significantly larger annual N2O emission from no-till soils and soils under corn was attributed to an episode of very high N2O emission following the application of fertilizer during a period of wet weather. That the N loss by N2O emission occurred only in no-till soils and was large and long-lasting (~4 wk) confirms the strong effect that management has in reducing fertilizer N losses. In 2005, tilled soils had significantly larger N2O emission than no-till soils, most of which was emitted before the end of June. Because the tilled soils were better aerated, nitrification was likely the primary process contributing to the larger emission. Relatively low N2O emission from soybeans suggests biological N fixation does not appear to contribute substantially to the annual N2O emission. Further study of methods to reduce N2O emission in agricultural systems should focus on improving N use efficiency within a particular tillage system rather than looking to differences between tillage systems.
