Measurement of nitrous oxide soil fluxes using sorbent-stabilized sampling of flux chambers

Authors: ZIMBRON, JULIO - E-Flux; Del Grosso, Stephen; Delgado, Jorge

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2025
Publication Date: 5/5/2025
Citation: Zimbron, J., Del Grosso, S.J., Delgado, J.A. 2025. Measurement of nitrous oxide soil fluxes using sorbent-stabilized sampling of flux chambers. Journal of Environmental Quality. https://doi.org/10.1002/jeq2.70036.
DOI: https://doi.org/10.1002/jeq2.70036

Interpretive Summary: Nitrous oxide is an important greenhouse gas emitted from cropped and grazed soils that is time consuming and difficult to measure using currently available methods. ARS and industry scientists tested an adaptation of sorbent-based sampling (using Zeolite 5A) to measure soil nitrous oxide emissions by comparing it with the standard chamber method. The modified method used a single large (400 mL) sample at the end of the chamber deployment (30 min), compared to taking three small (25 mL) grab samples during the same period. Gas concentrations measured by both methods at the end of the chamber deployment were in close agreement, with a correlation not significantly different than the ideal 1:1 relationship. Additionally, pooled sample results from four locations correlated well with those of average chamber deployments, demonstrating that the number of samples analyzed can be further reduced. These results suggest sorbent-based sampling yields soil gas flux data of similar quality to standard methods, with potential advantages of increased sample stability and reduced number of samples required.

Technical Abstract: This report tests an adaptation of sorbent-based sampling (using the sorbent Zeolite 5A, or Z5A) to measure soil gas fluxes using the standard chamber method (which normally use grab samples), with the goal to expand the chamber method beyond its current limitations. Both methods were field tested side-by-side in experimental plots in four separate dates. The modified method used a single large (400 mL) sample at the end of the chamber deployment (30 min), compared to taking three small (25 mL) grab samples during the same period. Large samples were field-stabilized by sorption. Standard method samples were lab analyzed by gas chromatography and thermal desorption/gas chromatography were used for sorbed samples. Soil gas fluxes were calculated using the measured gas concentrations and the GRACEnet protocols for the standard method and assuming linear increases in concentration for the sorbent method. Gas concentrations measured by both methods at the end of the chamber deployment (30 min) were in close agreement (R2 = 0.92), with a correlation not significantly different than the ideal 1:1 relationship (a=0.05). Also, calculated soil gas fluxes from sorbed samples were in agreement with those based on grab samples (R2 = 0.91). Additionally, four-100 mL samples were pooled into a single cartridge to explore the sorbent potential to further reduce the number of samples analyzed. Pooled sample results from four locations correlated well with those of average chamber deployments (R2 = 0.92 and R2 = 0.95 for N2O concentrations and soil gas fluxes, respectively). These results suggest sorbent-based sampling yields soil gas flux data of similar quality to grab sampling methods, with potential advantages of increased sample stability and reduced number of samples.