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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPACTS OF RISING ATMOSPHERIC CARBON DIOXIDE AND TEMPERATURE ON CROP GROWTH, REPRODUCTIVE PROCESSES, YIELD, AND SEED QUALITY Title: Determining aerodynamic conductance of spar chambers from energy balance measurements

Authors
item Monje, O - DYNAMIC CORP
item Allen, Leon
item Boote, K - UNIVERSITY OF FLORIDA

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 5, 2007
Publication Date: N/A

Technical Abstract: The aerodynamic conductance (gA) of SPAR chambers was determined from measurements of energy balance and canopy temperature over a peanut canopy. gA was calculated from the slope of sensible heat flux (H) versus canopy-to-air temperature difference. H and the canopy-to-air temperature were varied by manipulating chamber CO2 concentration or vapor pressure deficit. Net radiation was measured with a net radiometer, latent heat flux (LE) was calculated from evapotranspiration (ET), and H was calculated by subtracting LE from Rnet. Canopy temperature was measured using two Apogee infrared thermometers placed at the same height as the net radiometer. The average gA over a 34 day-old peanut canopy was 3.9 mol/(m-m-s). The ability to determine gA in the SPAR chambers allowed the separation of canopy stomatal conductance (Gc) from contributions due to leaf boundary layer conductance and turbulent mixing penetrating the vegetation. Canopy Gc was calculated from surface conductance (Gs) and gA. Gs was estimated from rates of LE. Gs of the 34 day-old peanut canopy was 0.45 mol/(m-m-s). The accuracy of the Gs measurements depends on the ability to measure the rate of soil evaporation within the chamber.

Last Modified: 10/22/2014
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