Nitrous oxide emissions from an annual crop rotation on poorly drained soil on the Canadian Prairies

Agricultural soils are a significant anthropogenic source of nitrous oxide (N2O) to the atmosphere. Despite likely having large emissions of N2O, there are no continuous multi-year studies of emissions from poorly drained floodplain soil. In the present study, the micrometeorological flux of N2O (FN) was measured over three years (2006–2008) in a maize (Zea mays L.)/faba (Vicia faba minor L.)/spring-wheat (Triticum aestivum L.) rotation in the Red River Valley, Manitoba, Canada on a gleyed humic verticol soil. Comparison of newly established reduced and intensive tillage treatments showed no difference in FN within the constraints of the high variability between duplicate plots. The annual gap-filled ΣFN across tillage treatments was 5.5, 1.4, and 4.3 kg N ha−1 in the maize, faba, and spring-wheat crop years, respectively. Emissions from fertilizer N addition and soil thaw the following spring was responsible for the greater ΣFN in the maize and spring-wheat years. Using four approaches to approximate background ΣFN resulted in estimates of 3.5–3.8% and 1.4–1.8% of applied fertilizer N emitted as N2O for the maize and spring-wheat crops, respectively. The CO2 global warming potential equivalent of ΣFN over the three study years was an emission of 5.4 Mg CO2-equiv. ha−1 which adds to the previously determined C balance emission of 11.6 Mg CO2-equiv. ha−1.

► N2O emissions occurred at thaw and shortly after fertilizer addition.
► N2O emission were 5.5, 1.4, and 4.3 kg N ha−1 in maize, faba, and spring-wheat years.
► Emissions with faba were lowest because of lack of fertilizer and thaw emissions.
► CO2 equiv. of N2O emissions were comparable to that for net emissions of CO2.
► Net N2O and CO2 emissions resulted in 22.8 Mg CO2-equiv. ha−1 over the three years.