Infrared Heater Arrays for Temperature Free-Air Controlled Enhancement (T-FACE) of Open-Field Plots.

There is a need for methodology to warm open-field plots in order to study the likely effects of global warming on agricultural productivity in the future. One promising approach is to utilize arrays of infrared heaters with ceramic heating elements. Good uniformity of warming can be achieved across 3-m-diameter plots by tilting the heaters at 45 degrees from horizontal and combining six of them in a hexagonal array. Efficiency [η_h (%); thermal radiation out per electrical energy in] is strongly dependent on wind speed (u; m/s) and can be described by: η_h = 10 + 25exp(-0.17u). In additional tests of an array with triple the area (5m diameter) and triple the number of heaters (18), no scaling problems were encountered, the same efficiency equation was applicable, and excellent uniformity was again achieved. Three-m-diameter arrays have been deployed over plots of grazing land at Haibei, Qinghai, China and at Cheyenne, Wyoming, USA, and over wheat at Maricopa, Arizona, USA. The latter experiment is dubbed “Hot Serial Cereal”, where “Cereal” is because wheat is the crop, “Serial” because we are planting the wheat every six weeks for two years, and “Hot” because arrays of infrared heaters are being deployed on some of the planting dates. The target temperature regime of the infrared-warmed plots is 1.5 degrees C during daytime and 3.0 degrees 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 are to generate a dataset that will provide 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. Data on warming performances of the infrared heater arrays and of their electrical power consumptions at all three sites are presented.