All About Timing! Determining Measurement Duration for Soil Flux Measurements

The LI-8100A SoilFluxPro™ software provides a tool to analyze the effect of observation length on measured flux values. The LI-8100A Automated Soil CO2 Flux System can be set up with varying measurement settings to account for the specific measurement conditions. A typical survey or long-term measurement consists of an observation length of 1.5 to 2.5 minutes, and a deadband of 20-30 seconds. However, these typical settings should be optimized for the specific measurement. This is especially true for measurements of very low or very high fluxes and other trace gases besides CO2. SoilFluxPro software can be used to determine what the appropriate observation length and deadband should be for the measurement by looking at data from a few representative measurements. There are two options for doing this: manual adjustment and automated guidance. For each option the software gives you the choice to either keep the new results or revert back to the original computation.

For manual adjustment one can look at the detailed regression analysis view of an observation (below right) and move the green line (to adjust the dead band) or the red line (to adjust the stop time). This will change the data used for computation. New flux values are computed automatically as the lines are adjusted.

For automated guidance one can use the ‘Guidance’ tab on the detail observation view regression analysis window. Below we show the automated analysis of the effect of changing the start time (below left) and stop time (below right) on the flux. For this particular measurement an appropriate start time would be between 20 and 40 seconds. Computing the fluxes using a start time greater than 50 seconds would result in a significant change in the flux values. For the stop time the analysis shows that the computed flux value stabilizes after 100 seconds of measurements. This indicates that the measurement time could be limited to anywhere between 100 and 120 seconds.