Field Evaluation of Open System Chambers for Measuring Whole Canopy Gas Exchanges

The ability to monitor whole canopy CO2 and H2O fluxes of crop plants in the field is needed for many research efforts ranging from plant breeding to the study of climate change effects on crops. Four portable, transparent, open system chambers for measuring canopy gas exchanges were field tested on well‐watered and fertilized cotton (Gossypium hirsutum L.) over 6 d at Lubbock, TX, in 2010. Our objective was to (i) characterize changes in canopy microclimate variables due to chamber enclosure and (ii) evaluate chamber‐to‐chamber variability in canopy gas‐exchange parameters on ground as well as leaf area basis. Chamber wall materials reduced photosynthetically active radiation (PAR) by about 13%. Programmable data loggers controlled variable speed fans and, with one minor exception, limited heat buildup in the chambers to a maximum of