The flux (F) of nitrous oxide (N2O) and carbon dioxide (CO2) between the field plots and the atmosphere is determined by measuring the difference in air concentrations (ΔC) measured between two heights (Δz):
Each plot contains a tower with intakes installed at two heights, separated by a vertical distance (Δz). Tubing connects the intakes to a tunable diode laser trace gas analyzer (TGA100A, Campbell Scientific), housed in a trailer at the centre of the field site.
The TGA100A measures the air concentrations of N2O and CO2 at 10 Hz. A manifold system switches the concentration measurements between the upper and lower intakes at 15-second intervals for 30 minutes. Software processes this data to give a measurement of ΔC.
The manifold also switches the concentration measurements between four plots every 30 minutes to calculate 12 N2O and CO2 fluxes per plot, per day. The difference in concentration is scaled by the eddy diffusivity (K) to calculate a flux. K describes the degree of ‘mixing’ between the surface and the atmosphere. This is measured using sonic anemometers (Campbell Scientific CSAT3).