Spring and summer measurements of N2O flux from an agricultural field

The IPCC guidelines for calculating the emissions of N₂O associated with legume crops was reassessed recently and revised in Canada. This change has resulted in a reduction of the estimated emissions from Canadian agriculture by about 10 Gg of N₂O. In this study, we document how these revisions relate to data collected from a field cropped with peas followed by forage near Côteau-du-Lac, Quebec, Canada during 2003 and 2004.

Micrometeorological towers, associated with a roving measurement system designed for quantifying emissions from diffuse sources (i.e. agricultural fields), were used to measure greenhouse gas (GHG) fluxes at the field scale. Using a tunable diode laser trace gas analyzer, continuous measurements of N₂O were made during a complete spring, summer growing season and following spring period. Our study showed somewhat low emissions during the initial snowmelt period. The summer emissions were small and continuous. As expected, emission peaks were noted following fertilizer application and major rainfall events. While peaks following rainfall events were generally small, a rainfall event of 50 mm generated huge emissions. The largest recorded peak occurred after manure application and was sustained for almost 10 days.

The results of these experiments will be used for verifying GHG exchange models and updating coefficients used in calculating emissions in the national GHG accounting system for exchanges of agricultural origin in Canada.