Studies on the Variation of Heat Balance Characteristics of Water Layer under Plant Cover in Relation to the Luxuriance of Rice Plant
1964 Volume 19 Issue 3 Pages 89-95
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1964 Volume 19 Issue 3 Pages 89-95
It is expected that a plant canopy plays an important role in micrometeorological processes in and under the plant canopy. In this paper the author thus tried to clarify quantitatively the dependence of heat balance terms of a water layer under a paddy plant cover on the development of a plant canopy. The data for such an analysis were obtained from the observations of the evaporation and the transpiration from paddy fields in the early cultivation and the ordinary cultivation periods (1962).
The results may be summarized as follows:
1. Maximum value of leaf area index (L.A.I.) in the early and ordinary cultivations of rice plant was 4.5 and 5.0 respectively. As the density of plant cover increased, both the difference in temperature between water and surrounding air layer and the amplitude of diurnal variation of water temperatures under plant cover were gradually decreased. Daily mean water temperatures in the paddy field of the ordinary cultivation are above 30°C during the period from the middle of July to the middle of August, and such a high value in water temperature seems to be unfavorable to the growth of paddy rice in warmer regions of Japan.
2. Total sensible heat transfer coefficient varied seasonably and the daily mean of it decreased gradually from 1.5×10-4 to about 0.5×10-4ly/sec.°C. as the density of plant cover increases. These results were in good agreement with those obtained by UCHIJIMA (1961), KOTODA (1962).
3. The“storage ratio”defined as the ratio of heat amount stored in both soil layer and the water column to the net radiation supplied on the water surface can be expressed by Eq. (5). This equation implies that the storage ratio decreases with the increment of both the sensible heat transfer coeffieient h and the ratio β′. The observed values were in good agreement with the line of β′=5 which was calculated by inserting the following values, Sw=0.5ly/min., θw-θa=5°C in Eq. (5).
4. The relationships between evaporation from water surface under plant cover or transpiration from the plant cover and net radiation are shown in Fig. 3. The results obtained by the author are somewhat different from those obtained by UCHIJIMA (1961), the causes for the discrepancy should be investigated in detail.
5. By analyzing the dependence of variation of microclimatic conditions under plant cover on the increase and decrease of L.A.I., Eqs. (7), (8), and (9) were obtained. It is known from these equations that the microclimatic elements under plant cover are closely related to the density of plant canopy. This fact indicates that a density of plant canopy plays a significant role in micrometeorological processes within plant-air layer.
