Abstract:

 Whether irrigation water with low temperature could affect the temperatures of rice plants (including flag leaves, panicles and stems) under high air temperature remains unknown now. A field experiment was conducted with a split-plot design under field conditions. The experiment included four treatments, i.e. high air temperature with irrigation water of low temperature, high air temperature with irrigation water of normal temperature, natural air temperature with irrigation water of low temperature and natural air temperature with irrigation water of normal temperature, during which irrigation water temperature treatments were regarded as main plots (initial water temperature 20.0℃ for cold water irrigation treatment and initial water temperature 27.7℃ for irrigation with normal temperature) and air temperature treatments were seemed as subplots (the average air temperature 38.0℃ for high air temperature treatment and the average air temperature 32.0℃ for natural air temperature treatment). The change characteristics of rice plant temperatures and the effect of irrigation with cold water and normal temperature water on the temperatures of rice flag leaves, panicles and internodes were explored in this paper. The experimental results indicated that, under high air temperature, the temperatures of rice flag leaves, panicles and the internodes were markedly enhanced by 5.9℃, 5.7℃ and 0.9℃, respectively, as compared with those for natural air temperature. Under high air temperature, the water temperature for irrigation with cold water treatment increased faster and changed larger than that for irrigation with normal temperature water, with the former increasing by 6.0℃ from 10：00 to 15：00 while the latter increasing only by 2.3℃ from 10：00 to 15：00. The phenomenon suggested that the cold water could absorb more energy from surrounding environment than normal temperature water under high air temperature. Therefore, under high air temperature, the irrigation with cold water treatment pronouncedly decreased the temperatures of flag leaves, panicles and the internodes by 1.5℃, 1.3℃ and 1.6℃, respectively, furthermore, increased the temperature differences between air and flag leaves, between air and panicles and between air and internodes, as compared to those for irrigation with normal temperature water treatment. Irrigation with cold water could significantly reduce organs temperatures within rice plants under high air temperature, which played a key role in alleviating heat-stress. Correspondingly, it should be considered as a method to mitigate high air temperature damage in rice production. 

Key words: Irrigation with cold water, Rice, Flowering stage, Short-term high air temperature, Alleviation effect