ARS | Publication request: An open system for measuring canopy gas exchange

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract
Publication Acceptance Date: October 5, 2008
Publication Date: October 9, 2008
Citation: Baker, J.T., Lascano, R.J., Gitz, D.C., Payton, P.R., Van Pelt, R.S., Garcia, R. 2008. An open system for measuring canopy gas exchange[abstract]. ASA-CSSA-SSSA Joint Annual Meeting. Houston, Texas. October 5-9, 2008. Abstract No. 779-4.

Technical Abstract: Three portable, CETA (Canopy Evapo-Transpiration and Assimilation) chamber systems were built and evaluated in 2006. This chamber system is an open or flow-through system that, once deployed in the field, can operate unattended for extended periods (e.g. overnight for example). The CETA chamber consists of an aluminum framework, 1 m x 0.75 m in cross-section and 1 m tall covered with transparent film. Differentials between incoming and outgoing atmospheric water vapor and carbon dioxide concentrations are used to calculate evapotranspiration and canopy photosynthesis at 10 s intervals using solenoid valve actuated sample lines connected to an infrared gas analyzer. A programmable data logger controls fan speed and air flow rate in order to control chamber air temperature to within 0.5 ºC of ambient air temperature using a feedback control algorithm. In order to validate the mass balance equations used to calculate canopy evapotranspiration, the CETA chamber was placed over potted plants sitting atop a mini-lysimeter. A wide variety of crop canopies and soil water content were created with greenhouse-grown plants. Data analysis indicates good agreement between CETA evapotranspiration measurements and the mini-lysimeter over wide ranges of soil moisture contents and canopy leaf area.