OPEN-TOP CHAMBERS FOR FIELD STUDIES OF CROP RESPONSE TO ELEVATED CO2 AND TEMPERATURE

A new design for Open Top Chambers (OTCs) is described. In addition to providing CO2 controls as do several other existing OTCs, the system is designed to provide elevated temperature control. To provide a more natural vertical microclimate profile, the newly designed system pull s air down through the chamber and out the bottom rather than injectin g air at the bottom and venting it out the top of the chamber. A proto type was constructed and performance tests were conducted. Over a 24-h test period with a CO2 concentration setpoint of 660 ppm, individual measurements of concentration taken every 5 min averaged 660.5 ppm wit h a standard deviation of 26.6 ppm. Temperature controls were rested o ver 24-h periods for two different setpoints-ambient +4 degrees C and ambient +6 degrees C. For the two test periods the average chamber tem perature measurements were 3.98 degrees and 5.99 degrees C above ambie nt, respectively. Twenty chambers based on the prototype design were c onstructed and installed at the International Rice Research Institute, Los Banos, Philippines. As intended, the chambers are currently being used to conduct research on rice crop response to elevated CO2 and te mperature.