PARENT SESSION
Poster Session 39: Late Breaking and Newsworthy Posters
Friday, August 12, 8:30 AM - 10:30 AM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Soil CO₂ flux measurements: Comparison between the LI-COR LI-6400 and LI-8100.

Madsen, Rodney¹, Xu, Liukang¹, Demetriades-Shah, Tanvir¹, Garcia, Richard¹, McDermitt, Dayle^*,1, ¹ LI-COR Biosciences, Lincoln, NE, USA

ABSTRACT- Soil CO₂ flux is driven primarily by the CO₂ diffusion gradient across the soil surface. Ideally, the flux measurement should be made without affecting the diffusion gradient. In a closed-chamber system the slope of dCO2/dt is required to compute the flux. To obtain the slope of dCO₂/dt, the chamber CO2 concentration must be allowed to rise. Consequently, soil CO₂ flux will be affected because of the decreased CO2 diffusion gradient. To overcome this, LI-6400 and LI-8100 use two different approaches. In the LI-6400 system, chamber CO₂ level is scrubbed down slightly below the ambient concentration and then allowed to rise as CO₂ accumulates in the chamber. The flux is estimated while the chamber CO₂ is near the ambient level. The LI-8100 system is designed for long-term and unattended field measurement. Using chemical CO₂ scrubber is not desirable. Different approach is used to minimize the impact of altered CO₂ diffusion gradient on the measurement. In LI-8100 system, the chamber CO₂ concentration versus time is fitted with an exponential function, soil CO₂2 flux is then estimated by calculating the initial slope from the exponential function at time zero when the chamber touches the soil, and that is when the chamber CO₂ concentration equals to the ambient. Several experiments were conducted inside a greenhouse and in the open field under various conditions to compare soil CO₂ flux measurements made from the LI-8100 system and from the LI-6400 system under similar conditions, and we found that two systems agree with each other very well.

Key words: Soil CO2 flux, Closed chamber method, Diffusion gradient