Vergara - 1976 - Physiological and morphological adaptability of ri

126 curt-tyre AND RICE
tribution. It was found that the systematic decrease of energy with increasing
frequency agrees with the negative five-third power law of the similarity theory‘ of
turbulence. Figure 6A shows the energy spectra at 1.15 m height (above the canopy)
and at 0.2 m height (with the canopy) as plots of log (n - S(n)/s ,3) against
1og(n - zfu), xvhere n is the frequency, S(n) is the turbulent energy at the frequency
of n. The spectral curves for the 0.2 in height are much more ragged than those
for the 1.15 1n height. and have relatively more energy in the dimensionless
frequency range of6. 10" to 4 than the spectra for the 1.15 m height. The spectra
for 1.15 m height contribute mainly in the range of 4.10”- to 4.104 of the
dimensionless frequency. The eonsiderahlyj ragged nature of the spectra in the
canopy seems to result from the selective absorption and addition of turbulent
energy at certain characteristics frequencie by plant elements.
Figure 6A denotes also that the level of turbulent energy relating to the i11-
tensity of air mixing in the air is considerably‘ less in the canopy" than above the
canopy. implying that the magnitude of the turbulent transfer ctiefficient (K)
is diminished in the canopy. The following relation was used to determine the
values of K in a rice canopy (Uchijima. 1962a):
K(z) =
_ (Ridz)
_
Pfiiw ‘t
Jag
where R_(z), dTtdz, and dqldz are the net radiation. the vertical gradients of
air temperature. and specific humidity at a height of z. respectively‘. J, is the
rate of change of heat storage in water and soil layer. r ,, and C, are the density
of air and specific heat of air at constant pressure. and 1 is the latent heat of
vaporization. The profiles of K in a ricc canopy evaluated from Eq. (18) are
presented in Fig. 6B. Although the midday values of the diffusion coefficient
at the top of the crop were nearly three orders of magnitude greater than moleeular
diffusion coefficients, K decreased very rapidly to a value ofthe one order
of molecular diffusion coefficient near the water surface beneath the canopy.
The daytime extinction of K was expressed as a function ofhcight as follows:
m) = :¢>