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United States Department of Agriculture

Agricultural Research Service

Title: An open system for measuring canopy gas exchange

item Baker, Jeff
item Van Pelt, Robert - Scott
item Gitz, Dennis
item Payton, Paxton
item Lascano, Robert
item Mcmichael, Bobbie
item Garcia, Rick

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/8/2008
Publication Date: 4/10/2008
Citation: Baker, J.T., Van Pelt, R.S., Gitz, D.C., Payton, P.R., Lascano, R., Mcmichael, B.L., Garcia, R. 2008. An open system for measuring canopy gas exchange[abstract]. 38th Annual BSSG Conference. Temple, Texas. April 8-10, 2008.

Interpretive Summary:

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. Preliminary data analysis indicates good agreement between CETA evapotranspiration measurements and the mini-lysimeter over wide ranges of soil moisture contents and canopy leaf area. However, these tests also indicate a physical limitation of the system to resolve very small gas concentration differentials caused by the combination of very low soil moisture content and low canopy leaf area.

Last Modified: 06/21/2017
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