Measurement Technique Effects on Greenhouse Gas Emissions from Conventionally Tilled, Furrow-Irrigated Soybean on a Silt-Loam Soil

Agricultural greenhouse gas (GHG) fluxes are often measured using chamber-based methods. However, comparisons among chamber-based methods are limited. This study compared the effects of chamber type and GHG concentration measurement method on GHG fluxes, emissions, global warming potential (GWP), and reduced two-gas GWP (GWP*) in conventionally tilled soybean (Glycine max L. [Merr]) on a silt-loam soil (Aeric Epiaqualfs) in southeast Arkansas. Carbon dioxide (CO2) fluxes measured by optical feedback-cavity enhanced absorption spectroscopy (OF-CEAS, FT-LICOR) were greater (p < 0.01) than from the non-steady-state, non-flow-through, static, closed-chamber method analyzed by gas chromatography (NFT-GC), while methane (CH4) and nitrous oxide (N2O) fluxes were greater (p < 0.01) from the NFT-GC than the FT-LICOR method. Cumulative season-long CO2 emissions were 36.2, 31.6, and 13.7 times greater (p < 0.01) from the FT-LICOR than the NFT-GC method for 0–15, 0–30, and 0–60 min gas sampling intervals, respectively. Methane N2O emissions and GWP* did not differ (p > 0.05) between FT-LICOR and NFT-GC methods for the 0–15, 0–30, and 0–60 min intervals. Results suggest that differences in GHG flux, emissions, and GWP estimates reflect the combined influence of measurement methods rather than individual system components (i.e., chamber design, analyzer type, or closure time), which should be considered when designing and executing field studies.