Comparison of Simultaneous Soil Profile N2O Concentrations and Surface N2O Flux Measurements Overwinter and At Spring Thaw In An Agricultural Soil.

Nitrous oxide (N₂O) is a greenhouse gas with a 100-year GWP (global warming potential) that is 298 times stronger than CO₂ per mass, and is involved in the destruction of atmospheric ozone. In cold climates, after spring-thaw, large emissions of N₂O (often termed “bursts” or “flushes”) have been found to occur from agricultural soils. The understanding of the mechanisms behind these spring-thaw emissions is incomplete. Of particular importance is determining whether nitrous oxide is produced during freezing and released at thaw, or if it is produced at the onset of thawing. The objectives of this research are to compare changes in soil gaseous N₂O storage to the accumulated surface N₂O flux from field-scale measurements, and to estimate the contribution of the physical release of N₂O from soils upon spring-thaw to surface N₂O fluxes. A field experiment was carried out at the Elora Research Station in Ariss, Ontario from October 2010 to May 2011, where the experimental area consisted of a 150 by 100 m plot (conventional till with residue returned). Surface N₂O fluxes were measured through the use of a Campbell Scientific Trace Gas Analyzer employing the micrometeorological flux-gradient technique, and were calculated as half-hourly averages. Soil profile measurements were taken in four replicates at depths of 5, 10 and 15cm, consisting of: soil apparent heat capacity (heat pulse probes, additionally at 2cm), soil water content (water content reflectometers), soil temperature (thermocouples) and soil surface temperature (infared thermometers, surface only). Soil gas samples were taken manually at each replicate (using soil gas probes at depths of 5, 10, 15, 30 and 60cm) weekly overwinter and with increasing frequency approaching spring-thaw. Soil gas samples were analyzed in laboratory for gaseous N₂O concentration.  Results are pending and to be presented.