Infrared Heater Arrays (T-FACE) for Warming Open-Field Plots.

In order to study the likely effects of global warming on field-grown crops, a method is needed to warm open-field plots and create an environment like that expected in the future. One such T-FACE (Temperature Free-Air Controlled Enhancement) system that shows promise is to deploy hexagonal arrays of infrared heaters around the periphery of the plots at a height above the vegetation of 0.4 times plot diameter with the heaters tilted 45° toward the center of the plot. Using infrared thermometers to sense canopy temperatures in warmed and in unheated reference plots, a control system modulates power to the heaters to maintain a set level of warming above the reference plot. Starting in March, 2007 and utilizing arrays with six 1000W heaters, we initiated a “Hot Serial Cereal” experiment where “Cereal” is because wheat was the crop, “Serial” because we planted the wheat every six weeks for two years, and “Hot” because infrared heaters were deployed on selected planting dates. The target temperature regime of the infrared-warmed plots was 1.5° C during daytime and 3.0°C at night above that of reference plots with dummy heaters. By exposing wheat to a huge range of natural and artificially imposed temperatures, our objectives were to generate a dataset that provides stringent tests of the temperature aspects of wheat growth models and to assess whether infrared heating results in plant responses similar to those from natural variations in air temperature. The uniformity of the warming treatment across the 3-m plots was excellent. For the crop planted on 13 March 2007, the T-FACE systems provided warming within +/- 1.0°C of the setpoint differences 79% and 82% of the day- and night-times, respectively. Deviations from the setpoints were largely attributable to high winds or situations when the characteristics of the canopies of the heated and reference plots differed substantially. Annual electrical power costs were about $3,000 per plot.