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United States Department of Agriculture

Agricultural Research Service

Title: Evapotranspiration Measurement in Controlled Environment Chambers: a Comparison Between Time Domain Reflectometry and Accumulation of Condensate from Cooling Coils

item Kim, Soo Hyung

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: November 7, 2005
Publication Date: November 7, 2005
Citation: Timlin, D.J., Kim, S., Fleisher, D.H., Reddy, V. 2005. Evapotranspiration measurement in controlled environment chambers: a comparison between time domain reflectometry and accumulation of condensate from cooling coils [abstract]. ASA-CSSA-SSSA. CD-ROM.

Technical Abstract: Controlled environment chambers are an important research tool to quantify canopy level phototsynthesis under controlled temperatures. Because the chambers are isolated from the atmosphere, fluxes of CO2 and water vapor in and out of the chamber are minimized. This allows for precise measurement of CO2 assimilation rates to quantify photosynthesis as CO2 can be easily metered and measured. The measurement of water fluxes is carried out by measuring condensate draining from cooling coils and depends on maintaining a constant humidity in the chambers. This provides a direct measure of evapotranspiration. However, in growth chambers with soil bins, this does not give information on root activity with soil depth. In this study we also instrumented the soil bins with time domain reflectometry probes that were controlled by an automated system. The soil water content was monitored once an hour at five vertical depths with three measurement locations per depth. Varying amounts of irrigation water were applied to the plants (corn and potato). The differences between the methods were larger when the plants were small and decreased as canopy cover increased. The hourly changes in soil water content lagged behind the changes in water accumulated from the cooling coils. The correlations between the two methods were best for well watered treatments and decreased for treatments having limited irrigation.

Last Modified: 9/10/2014