Controlled warming effects on wheat growth and yield: field measurements and modeling

Authors: GRANT, ROBERT - University Of Alberta; Kimball, Bruce; Conley, Matthew; White, Jeffrey; Wall, Gerard - Gary; OTTMAN, MICHAEL - University Of Arizona

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2011
Publication Date: 10/1/2011
Citation: Grant, R.F., Kimball, B.A., Conley, M.M., White, J.W., Wall, G.W., Ottman, M.J. 2011, Controlled warming effects on wheat growth and yield: field measurements and modeling. Agronomy Journal, 103(6):1742-1754.

Interpretive Summary: R.F. Grant, B.A. Kimball, M.M. Conley, J.W. White, G.W. Wall, and M. J. Ottman In order to predict the likely effects of global warming and other factor on the future productivity of wheat and other crops and unmanaged vegetation, the ecosystem model, ecosys, was developed. It was tested against data from, a “Hot Serial Cereal” experiment – “Cereal” because it was on wheat, “Serial” because the wheat was planted serially approximately every six weeks for two years, and “Hot” because on three of the planting dates each year, infrared heaters were deployed above the crop to warm it by 1.5°C (2.7°F) during daytime and 3.0°C (5.4°F) at night. The results showed that for normal planting dates (Dec.-Jan.), the extra infrared heating had no significant effect on the wheat growth. For late-planted wheat (Mar.) yields were generally depressed because of the shortened growing season, and the extra warming from the heaters exacerbated the yield depression. In marked contrast, for early-planted wheat (Sep.), mid-winter frosts reduced yields of unheated plots to zero, whereas the wheat under the heaters had yields only slightly depressed compared to the optimally planted wheat. ecosys was able to simulate the effects of both the varied planting date and the supplemental heating very well, which means it is a useful tool for assessing likely impacts of global warming on crop production and for developing adaptation strategies. This research will benefit all consumers of wheat-based food, including meat from animals that are fed wheat.

Technical Abstract: Climate warming may raise wheat yields in cooler climates and lower them in warmer. To understand these contrasting effects, infrared heating lamps were used to warm irrigated spring wheat by 1.5 'C (day) and 3.0 'C (night) above unheated controls during different times of the year at Maricopa, AZ. Changes in wheat growth with warming were used to test hypotheses for temperature effects on crop growth in the process model ecosys. Infrared heating substantially raised phytomass growth and grain yield under lower air temperatures (Ta) following plantings from September through December. However the same heating lowered growth and yield under higher Ta following plantings from January through March. Gains in wheat yield of as much as 200 g C m-2 with heating under lower Ta were attributed in the model to more rapid CO2 fixation and to reduced chilling effects on seed set. These gains were only partially offset by losses from shortened wheat growth periods. Losses in wheat yield of as much as 100 g C m-2 with heating under higher Ta were attributed in the model to adverse effects of heating on crop water status and on CO2 fixation vs. respiration, to greater heat stress effects on seed set, and to shortened crop growth periods. Model hypotheses thus explained contrasting effects of heating on wheat yields under different Ta found in the field experiment, as well as in many earlier studies. Well-constrained tests of these hypotheses are vital for models used to project climate change impacts on agricultural ecosystems.