Submitted to: Biological Systems Simulation Group Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/18/2011
Publication Date: 4/21/2011
Citation: Baker, J.T., Gitz, D.C., Payton, P.R., Lascano, R.J. 2011. Measurements of CO2 and H2O fluxes of crop plants are essential to understand the impacts of environmental variables on crop productivity[abstract]. Biological Systems Simulation Group Proceedings, April 18-21, 2011, Austin, Texas, p.1. Interpretive Summary:
Technical Abstract: Measurements of CO2 and H2O fluxes of crop plants are essential to understand the impacts of environmental variables on crop productivity. A portable, CETA (Canopy Evapo-Transpiration and Assimilation) chamber system was built and evaluated at Big Spring, TX. This chamber system is an open or flow-through system that, once field deployed, can operate unattended for extended periods. The CETA chamber consisted 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 H2O and CO2 concentrations were used to calculate canopy transpiration (E) and net assimilation (A) at 10 s intervals using solenoid valve actuated sample lines connected to an infrared gas analyzer. A programmable data logger controlled fan speed and airflow rate to control daytime chamber air temperature to within 0.5 ºC of ambient air temperature using a feedback control algorithm. The use of the variable speed fan to limit heat buildup during the day was found to be feasible provided there is sufficient leaf area and soil water for latent energy removal from the system. To validate the mass balance equations used to calculate E, the CETA chamber was placed over sealed soil potted cotton plants resting atop a weighing scale. A similar weighing scale, external to the chamber, was used to measure E of cotton plants outside the chamber in order to quantify potential “chamber effects”. A wide range of crop canopy leaf areas and soil water content were created with greenhouse-grown plants for both of these comparisons. Six identical chambers were constructed and tested in the field on subsurface drip irrigated cotton at Lubbock, TX in 2010. In addition to quantifying the degree of crop drought stress in terms of canopy gas exchanges we also compared CETA responses with simultaneous leaf-level gas exchanges made with two automated LI-6400 portable photosynthesis systems. In this discussion, we focus primarily on these field measurements.