RELATIVE IMPORTANCE OF AIR AND FLOODWATER TEMPERATURES ON THE DEVELOPMENT OF RICE (ORYZA-SATIVA)

Plants of rice (Oryza sativa) cultivar IR36 were grown under flooded and free-draining conditions at a constant air temperature of 28 degrees C with an 11.5 h d(-1) photoperiod in both a growth cabinet and a glasshouse. The nutrient solution within flooded pots was maintained at 20 degrees, 24 degrees or 28 degrees C, or was not controlled. Rate of floral development was enhanced by warmer nutrient solution temperatures at the same air temperature; times to panicle emergence were reduced by an average of 17 d with increase in the nutrient solution temperature from 20 degrees to 28 degrees C. In comparable treatments, plants grown in the growth cabinet reached panicle emergence later than those grown in the glasshouse, possibly because mean air temperature was on average 0.8 degrees C cooler in the growth cabinet. An independent model, derived from a previous investigation, provided a good prediction of the times from sowing to panicle emergence for plants grown in both the glasshouse and the growth cabinet when based on the mean of the temperatures of the nutrient solution and the air, showing that it is important to determine water/root temperature as well as air temperature when investigating the effect of environment on development of the rice plant.