Wheat Growth Response to Increased Temperature from Varied Planting Dates and Supplemental Infrared Heating

Possible future increases in atmospheric temperature may threaten wheat (Triticum aestivum L.) production and food security. The purpose of this research is to determine the response of wheat growth to supplemental heating and to seasonal air temperature from an unusually wide range of planting dates. A field study was conducted at Maricopa, AZ, where wheat was planted from September to May over a 2-yr period for a total of 12 planting dates. Supplemental heating was provided for 6 of the 12 planting dates using infrared heaters placed above the crop which increased canopy temperature by 1.3 degrees C during the day and 2.7 degrees C during the night. Grain yield declined 42 g m(-2) (6.9%) per 1 degrees C increase in seasonal temperature above 16.3 degrees C. Supplemental heating had no effect on grain yield for plantings in winter (Dec./Jan.) since temperatures were near optimum (14.9 degrees C). However, in spring (Mar.) plantings where temperature (22.2 degrees C) was above optimum, supplemental heating decreased grain yield from 510 to 368 g m(-2). Supplemental heating had the greatest effect in the early fall plantings (Sept./Oct.) when temperature was slightly below optimum (13.8 degrees C) and mid-season frost limited the yield of unheated plots to only 3 g m(-2) whereas yield of heated plots was 435 g m(-2). Thus, possible future increases in temperature may decrease wheat yield for late plantings and shift optimum planting windows to earlier dates in areas of the world similar to the desert southwest of the United States.