Vergara - 1976 - Physiological and morphological adaptability of ri

MILTRLICLlKili-YTE 0F THE RICE CROP 129
Ta, w = Zrr/ru is the angular velocity’ of temperature tvave, In is the period of
temperature xvave. and d is the water depth. The results obtained from the above
relation agreed well with measurements in shallow waters (Mihara et al, 1959).
Uehijima (1959) proposed also the following to relate the difference in mean
temperature between flooded water and the air with meteorological factors:
AT : Tw _' Ta : “Rum _ cl/pacpDa T‘
where RM. and G are the daily" means of net radiation above flooded water and
of soil heat flux, respectively‘, and 5e is the water vapor deficit. Results obtained
from Eq. (20) agreed well with observations and were used to evaluate the
geographical variation of water temperature of paddy fields (Uehijirna, 1959.
1962b, 1963). During the summer with strong radiation, the daily‘ mean water
temperature was higher than the mean air temperature, implying that heat energy
yvas consistently" transferred from the water surface to the air. The difference
in temperature between water and air increased gradually with the move~
ment from lower latitude to higher latitude. because ofthe decreasing value of r .
Sato (1960) observed profiles of temperature in clear and turbid water with a
depth of 5 ein, in relation to the prevention of damage by" exceptionally high temperatures
in flooded water as observed in southern Kyushu during midsummer.
Part of his measurements are reproduced in Fig. TB. The temperature in clear
“tater is uniform throughout at all times. On the either hand, the temperature in
turbid water exhibits inverse profiles during daylight. but the profiles at night
are the same as those observed i11 the clear water layer. Rose and Chapman
(1968) and Chapman (1969) also observed the temperature profiles in clear and
turbid waters, and found that the turbidity" of water is effective in lowering water
temperature.
The energy’ balance of rice fields has been studied to estimate water use by rice
plants and to elucidate characteristics of the energy partition of rice fields The
redistribution of radiant energy’ absorbed by crops is tisually’ expressed as follows:
R,,=1E+C+J+G