An FTIR-Based System for the Semi-Continuous Measurement of Greenhouse Gas Fluxes from Agricultural Soils.

Field plots were established at the Canada-Saskatchewan Irrigation Diversification Centre (CSIDC) near Outlook, SK. The main treatment consisted of a split application of urea applied at rates of 0, 55, 110, 165, and 220 kg N/ha (n = 20)—with half the fertilizer applied prior to seeding (broadcast and incorporated) and the remainder applied as a topdress just prior to bolting. Greenhouse gas (N₂O, CO₂, CH₄) fluxes from these plots were monitored on a semi-continuous basis using an automated flux chamber system consisting of a Fourier Transform InfraRed (FTIR) gas analyzer interfaced to a series (n = 20) of automated flux measurement chambers (AFC). To increase temporal resolution, two AFC-FTIR systems were deployed, with each interfaced to 10 chambers and each chamber sampled over a 20-min deployment period. This resulted in six to seven measurements per plot per day over a 170-d sampling season. Each system was calibrated against a standard gas three times daily to account for any measurement bias associated with the analyzers. Each automated chamber was also connected to temperature and moisture probes, the data from which were recorded during each flux measurement period. Gas fluxes were calculated using the SoilFluxPro software provided by LiCor (Lincoln, NB). Greenhouse gas fluxes also were measured using a manual flux chamber system (MFC; with GHG analysis performed using gas chromatography). Cumulative (seasonal) emissions were calculated using an Area-Under-the-Curve (AUC) analysis applied to the daily flux vs. time (day of year) data. Whereas flux data obtained using the AFC-FTIR system had a very high temporal density (n = 876) relative to the data obtained using the MFC-GC (n = 43), cumulative (seasonal) N₂O emissions calculated using the two systems were not significantly different. Data obtained using the AFC-FTIR system, however, provide much greater detail that could be of value in refining emission models.