Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2012
Publication Date: 10/9/2012
Citation: White, J.W., Kimball, B.A., Wall, G.W., Ottman, M.J., 2012. Cardinal temperatures for wheat leaf appearance as assessed from varied sowing dates and infrared warming. Field Crops Research, 137:213-220.
Interpretive Summary: Agricultural researchers often seek to predict how normal and extreme temperature conditions will effect crop growth and final yield. Accurate data on how crops respond to temperatures are essential for improving our ability to make such predictions. Air temperatures can be precisely regulated in controlled environment chambers, but chambers seldom provide lighting, wind and humidity conditions that accurately match field conditions. This raises concerns as to whether responses measured in chambers accurately reflect what happens in producers’ fields. To expose wheat crops to a very wide range of temperature conditions, we planted wheat at 15 dates in Maricopa, AZ, where daytime temperatures frequently exceed 100°F. To further increase the range of temperatures, in six planting dates, we provided artificial warming treatments using infrared heaters positioned in a hexagon above the wheat plants. Previous reports have described the effects of these treatments on grain yield, photosynthesis and crop development. This paper focuses on temperature effects on leaf number and tests the efficiency of different equations for describing the temperature effect on leaf appearance. The best equation suggested that leaf development stops when the daily mean air temperature is below 35°F and that the optimum temperature is 72°F. Attempts to use more complex equations that might improve description of responses at temperatures over 90°F performed poorly. This likely reflected the low frequency of data from mean air temperatures over 80 °F and possible severe stress responses at extreme high temperatures. The work demonstrates the value of such planting date studies at Maricopa and also suggests that more data from high temperature plantings are needed.
Technical Abstract: Accurate data on crop responses to temperatures are essential for predicting the potential impacts of climate extremes. Air temperatures can be precisely regulated in controlled environment chambers, but chambers seldom provide realistic radiation, photoperiod, wind and humidity regimes, which raise concerns as to whether responses quantified in such environments accurately reflect field performance. Field experiments employing sowing date (SD) and artificial warming treatments can provide a wide range of temperature regimes under otherwise natural field conditions. We analyzed temperature effects on main stem leaf appearance for the spring wheat (Triticum aestivum L.) cultivar Yecora Rojo using 15 sowing dates at Maricopa, AZ, USA. Six dates included infrared-based temperature free-air controlled enhancement (T-FACE) warming treatments. Mean air temperatures over the 15 periods of measurement varied from 11.6 to 33.2 °C. For comparisons among four segmented linear functions, a quadratic function and two forms of the beta function, the best fit to the data was for a two-segment function with a base temperature (Tbase) of 1.9 °C and an optimum (Toptl) of 22.2 °C. In attempting to estimate a second, upper temperature for maximum development (Toptu), the estimation process failed. This likely reflected the low frequency of data from mean air temperatures over 25 °C and possible severe stress responses at extreme low and high temperatures.