Nitrous Oxide Fluxes Measured by Micrometeorological Techniques in a Barley Crop.

Uncertainty about nitrous oxide (N₂O) emission factors remains high and there is a need for more data. In particular, large emission events during spring thaw and after fertilisation contribute greatly to the annual total. Characterising the effect of management practices on N₂O emissions is also desirable, which requires measurements on multiple plots.

Much of the data on N₂O emissions come from chamber methods, which have advantages but nevertheless disturb the surface environment and are physically difficult to implement at times. Micrometeorological methods have the advantage of not disturbing the surface. Two micrometeorological techniques for measuring N₂O emissions are flux-gradient and eddy covariance. The flux-gradient technique is convenient for measuring N₂O flux continuously and simultaneously from multiple large plots using a single analyser. However, the technique relies on assumptions about the relationship between vertical gradients and fluxes. Eddy covariance, in contrast, has a robust theoretical basis and requires fewer assumptions. However, it requires the N₂O sensor to be located near the measurement tower, limiting measurements to a single plot per analyzer.

In this work we measured N₂O flux from winter barley in Ontario, Canada, during spring thaw and after nitrogen fertilisation. Gradient and eddy covariance approaches were used simultaneously with two tunable diode lasers. Fluxes from each method are presented and discussed.