Tandem Measurements of CO2, O2, N2O and N2O Isotopomers on an Agricultural Field.

Agricultural fields are complex systems, often exhibiting spatially and temporally heterogenous greenhouse gas emissions patterns. Methods using static gas flux chambers tend to capture the spatial variability, but cannot obtain high temporal resolution data because of the labour involved in deployment. In agricultural systems, where event driven (i.e. fertilization, precipitation) pulses of greenhouse gas emissions dominate the annual greenhouse gas budgets, the lost resolution of static chamber approaches can negatively affect results.

Until recently, measurement of greenhouse gases in situ was not practical and discrete gas samples had to be taken back to the lab for analysis. Now, state-of-the-art laser based systems that simultaneously measure CO2, CH4 and N2O are available, opening up a new avenues of research that can be conducted in situ with good time resolution and accuracy. These laser based systems have shown comparable accuracy to traditional methods like Gas Chromatography (GC), but also benefit from the increased frequency of measurement, lowering the Minimum Detectable Flux limit.

Here, we use a soil amendment site to show how the increased measurement frequency of laser-based instruments can alter estimates of greenhouse gas emissions. The site consists of nine lysimeter cells with 3 levels of soil organic matter amendments that we hypothesize will impact the magnitude and timing of N mineralization and of sporadic N2O emission events. We will employ a Picarro G5501-i to make measurements of the N2O isotopomer flux, using the N isotopomers to identify mechanisms of N2O production. In addition, we present subsurface dynamics captured by nine soil gas wells, installed in each lysimeter cell, which continuously measured CO2 and O2 concentrations and N2O isotopomers. We conclude with a discussion of how the use of these high-resolution instruments in the field allowed us to detect substantially smaller fluxes compared to traditional techniques.