Rice Canopy Air Temperatures in a Texas Field.

Rice crop yield is reduced when periods of excessive heat coincide with reproductive development. Such periods occur in the Gulf Coast rice-growing region and elsewhere in the Southern U.S.; these are predicted to increase in frequency as part of global climate change.  The temperature conditions of primary interest are those that the panicles are subjected to at critical stages of development, however most predictions of crop response to temperature are based on weather-station data, which typically differ from in-field conditions due to canopy influences on the microclimate.

Under the leadership of the National Institute of Agro-Environmental Sciences of Japan, an international network was established in 2010 to monitor the canopy environment of rice paddies throughout sites in Asia using common measurement practices. In addition, a site at Beaumont, Texas, USA, was included. The canopy temperatures and relative humidity of all sites were monitored during reproductive development using a stand-alone, force-ventilated measurement system developed for this purpose.

At two of the sites, China and Texas, the relative humidity above the canopy exceeded 75%, and the air temperature in the canopy was close to (China) or exceeded (Texas) the above-canopy temperature. Across the sites, the daily mean air temperature at the nearby weather station typically exceeded that above the canopy, which in turn exceeded that in the canopy. However, the magnitude of these differences varied among sites. For example, in the Philippines, the difference between the weather station and in-canopy daily mean air temperatures was 2.4°C, whereas in Texas the difference was 0.8°C. The direct application of weather station data in heat-stress studies will result in errors, especially in comparisons among sites.