A Novel System for High-Resolution, Near-Continuous Measurement of Soil N2O Isotope Fluxes.

Measuring soil N₂O flux in field experiments is a major challenge. Most previous investigations have relied on laborious manual measurement campaigns, which, despite the large effort required, often do not provide data with high enough spatial and temporal resolution to capture ephemeral and/or localized changes in trace gas emissions. 

We have developed an automatic gas flux measurement system that can monitor soil N₂O emissions at high temporal resolution over extended periods. The system comprises a set of custom-designed automatic chambers, circulating gas paths and an N₂O Isotope Analyzer (Los Gatos Research, Inc., Model 914-0027). Chambers operate automatically at user specified sampling frequency with automatic interrupt for rain events. Current system design allows for up to 15 user programmable soil gas chambers. System digital logic, power conditioning, and measurement instruments are housed in a climate-controlled trailer allowing field deployment over extended periods. Wide dynamic range and parts-per-billion precision of OA-ICOS laser absorption instrument allows for extremely rapid estimation of N₂O fluxes. Current operational settings provide measurements of N₂O and its isotopes every 20 seconds with a precision of 0.1 ± 0.050 PPB. Sampling period of each chamber is programmable and can be made adaptable to measured flux rate. The system runs continuously, with current settings providing 12 daily flux measurements for each chamber and atmospheric samples every 20 minutes.  System performance is exemplified with data collected from a split-N, corn-soybean experiment in Columbia County, WI.

Accurate estimation of cumulative soil N₂O flux requires understanding “hot moments” that can account for a large portion of total emissions. Understanding the mechanisms controlling these ephemeral flux events requires automatic measurement techniques that can produce data with high time and spatial resolution, such as the novel system described.