P2.11
Study on the characteristics of rice paddy water temperature and its relation to dew formation on leaves
Tsuneo Kuwagata, Tohoku National Agricultural Experiment Station, Morioka, Iwate, Japan; and T. Hamasaki and T. Watanabe
Water temperature of a rice paddy is one of the most important factor affecting the growth of rice plants. The water temperature is influenced not only by weather conditions, but also by the canopy density which gradually increases during the growing season. In this study, we investigated the characteristics of the water temperature of a rice paddy. The results are summarized as follows:
(1) Water temperature of the rice paddy was vertically uniform, except for some specific conditions. Only when the depth of water layer was deeper than 10 cm and LAI (LAI: leaf area index including leaf sheaths) was greater than 2, the daytime water temperature at the surface was 2 - 3 oC higher than that at the bottom under fine weather condition (daytime solar radiation > 20 MJ m-2).
(2) Under the sunny weather, the daily mean water temperature depended on the wind speed as well as the canopy density. That is, under the strong wind conditions (daily mean value > 1.7 ms -1 at a height of 2.5 m above ground), the water temperature of the paddy field (TW) was 0 - 1oC higher than that of a non-vegetated water surface (TW0) for 0 < LAI < 2.0, while TW was lower for LAI > 2.0. Under weak wind conditions (< 1.7 m s-1), TW monotonously decreased with increasing LAI for all LAI ranges. On the other hand, under the cloudy weather, there were no significant differences between the WT and WT0 for all LAI ranges. The temperature difference between the water surface and air was also smaller under such conditions. These characteristics of the water temperature can be explained by the heat and radiation budget at the water surface, and also can be simulated by the heat balance model for vegetation canopy.
(3) The amplitude of daily variation of water temperature decreased with increasing depth of water layer, resulting in the lower water temperature in the daytime and higher in the nighttime for the deep water layer. For the rice paddy with deep water layer, higher water temperature in the nighttime depressed dew formation on the leaves.
Poster Session 2, Formal Viewing
Thursday, 17 August 2000, 1:30 PM-1:30 PM
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