Plant leaf consists of three components; dry tissue, water solution, and air. Therefore, the dielectric constant of leaf should be a function of the dielectric constant and the volume ratios of each component.
Dielectric constant of water is much larger than those of dry tissue and air so that the dielectric constant of the leaf is mainly due to the moisture ratio.
The leaf dielectric constant K was presented in the following equation
K=K_aP+K_t(1-P)+(K_w-K_a)(1-P)_ρtu,
where
K_a, K_t, K_w=dielectric constants of air, dry tissue and water, respectively
P=porocity of leaf
ρ_t=density of dry tissue
u=moisture ratio of leaf.
The electric capacity of Citrus leaves was measured by a parallel plate condenser holding a leaf between the plates at constant distance. By measuring the moisture ratio of leaf by weighing method, it was found that the apparent dielectric constant of the leaf was proportional to the moisture ratio.
The influence of insolation and wind on the apparent dielectric constant of the leaves of cut-branches put in water was studied. When the air and the water temperatures were temperate, the dielectric constant varies slightly with time However, when the air temperature was temperate and the water was cooled to 0°C, the dielectric constant decreased at a constant rate with time, which suggests drying of the leaf.

View full abstract

In the present paper, we discussed the heat balance of the glasshouse and the air temperature difference between the inside and the outside of the glasshouse which were developed from BUSINGER's (1963) equation. The temperature difference between the inside and the outside of the glasshouse (θ_in-θ_ou) is expressed by eq. (8), that is,
θ_in-θ_ou=h_in(H_net-_wH_ev)+β{h_ou·glH_net-(h_in+h_ou)(_glH_so+_glH_ev)}/h^sven(h_in+h_ou)+h_inh_ou (8)
where h_in is the heat transfer coefficient of the inside wall surface, H_net is the net irradiation at the outside wall surface, _wH_ev is the heat due to condensation at the inside wall surface, β is the ratio of the ground surface area to the wall surface area, h_ou is the heat transfer coefficient of the outside wall surface, _glH_net is the net irradiation at the ground in the glasshouse, _glH_so is the heat flux into the soil, _glH_ev is the latent heat flux density at the ground, and h^s_ven is an equivalent coefficient of the sensible heat exchange due to ventilation. A typical estimated example obtained from this equation is presented in Fig. 2.
Furthermore, the relations between our equations and those of YABUKI and IMAZU (1961), BUSINGER (1963), UCHIJIMA (1964, 1965), SUGI and TAKAKURA (1965), WALKER (1965), and KITAMURA (1967), are also demonstrated.

View full abstract

This paper is presented, not so much as an end in itself concerning the solution of a definite engineering problem, but as an exploratory step toward the solution to the problem of the linear response of plant to the wind. The problem of determing behavior of the response of plant to the wind is treated by spectral analysis theory.
The main result of the paper is that equations determining the relation between turbulent wind and linear response of plant are obtained under the appropriate assumption that the plant is fixed at one end. The author's intention was to illustrate by these results that the linear response problem of plant to the wind is solved easily by use of spectral function. The results obtined give some insight into what can be expected in the more general case of linear response of plant to the wind.

View full abstract

In order to make clear the dependencies of parameters Z₀ and d in the wind profile equation on wind velocity, some measurements over a sorgo canopy were carried out in Fukuoka Prefecture in 1-30August 1967, at the several different growth stages of sorgo plants, i.e., (I) August 1-5, (II) August 15-20 and (III) August 28-29.
A fairly wide range of values both of the roughness length (Z₀) and of the zero-plane displacement (d) were obtained from the log-profile analyses. The relationships of both Z₀ vs. u₄ (wind velocity at 4m height above the ground) and d vs. u₄ were examined for each period. We found a decrease in d and an increase in Z₀ with the increase in the wind velocity. These results are in good agreement with those of reported by UDACAWA (1966) with the barley fields. However, complicated changes in d and Z₀ for rice fields such as obtained by TANI (1960) were not found by present authors. Furthermore, the relation between d, Z₀ and H are analysed in the light of TAKEDA's theory (K. TAKEDA (1966)), where H is an effective plant height defined by the following equation:
1/H-dlnH-d/Z₀=K²/αH.
Plotting the values of d and Z₀ on the rough surface diagram introduced by TAKEDA, a curved line segment is obtained which shows variations of d, Z₀ and H in the course of a day. Also the place of the segment itself in the diagram changes with the development of the canopy. The change in the canopy structure or in the aerodynamical characteristics of the canopy surface seems to reflect in the values of Z₀ and d. Thus, it is shown that Z₀ increases with the growth, especially after heading. On the other hand, it is shown that d increases before heading, and then that after heading it decreases slightly, even though the plant height becomes continuously larger.
If we plot d and Z₀ against the friction velocity u_*, similar relations with those of d vs. u₄ and Z₀ vs. u₄ are obtained. Moreover, the effective plant hight H decreases with the increase in the friction velocity u_*, which is expected in TAKEDA's theory. Hence it may be concluded that the theory is appropriate also in this case of the sorgo canopy.

View full abstract

In order to reduce the wind damage to citrus trees caused by typhoons in the experimental field of the Shizuoka Citrus Experiment Station, peolple are planning to make some modifications in the arranging of Station buildings of local topographical characteristics.
To evaluate the effects of such modifications beforehand, the model experiments with wind tunnel were carried out by present authors.
We prepared four models of the scale of 1/1, 000, of which one is corresponding to the present status without any modifications and other three are corresponding to ones with the possible modifications such as removal of buildings, setting new banks, wind breaks and flattening small hills.
At first, the results of wind tunnel test with the unmodified model with respect to the distribution of wind speed and direction were compared with those obtained in the natural field, and we found a satis-factorily good similarity between them.
With the modified three models the characteristics of the respective wind fields as well as those of deposition patterns of fine particles introduced in the wind tunnel flow were investigated. The latter are assumed to respresent the accumulation of salty rain drops from the nearby sea surface, which may cause severe damages to citrus trees.
From the detailed investigations of numerous experimental results some recommendations to the possible modifications to the Station to be newly built have been obtained.

View full abstract

Biometrical data of the leaf area density and spatial distribution of the leaf area in corn crop fields were used to calculate penetration of the direct solar radiation into the canopy, the effective leaf area function, sunlit leaf area index and the intensity of the direct solar radiation falling on leaf surtace. The leaf orientation function was obtained with a silhouette method described in a previous paper (UDAGAWA et al., 1968).
The relation proposed by Ross and NILSON (1965) was used to determine the penetration of the direct solar radiation from the data of the leaf orientation and the direction of the sun. For simplicity, the following relation was used to obtain the effective leaf area function:
G_L(w)=∑6j=1∑8k=1g_L(w, θ_Lj, φ_Lk)|cosr₀r_L|jk,
where g_L(w, θ_Lj, φ_Lk) is the leaf normal distribution function, |cos r₀r_L|jk cosine of the angle between the leaf normal r_L and the direction of the sun r₀, and w the depth in the canopy. The mean extinction coefficient (k_d) for attenuation of the direct solar radiation within the canopy was determined from
k_d=cosech₀G_L,
where G_L is the mean effective leaf area function and h₀ the sun altitude.
The analysis indicates that the profile of the effective leaf area function changes with sun altitude. When the canopy was relatively sparse, the profile at the low sun altitude was found to be concave against z-axis, indicating that both the upper and lowest layers of the canopy were more penetrative compared with middle layers. On the other hand, the profile was convex when the sun altitude was higher than 45° This means that the direct solar radiation is strongly diminished in both the upper and lowest layers. When the sun altitude was between 30° and 40°, the profile became approximately constant and the value was about 0.5, implying that the canopy behaved to the direct solar radiation like a random orientation canopy in which the spatial distribution of leaves is non preferential as to both the inclination angle and azimuth angle. The diurnal change in the profile G_L(w) fade gradually away with development of the canopy as can be seen in Fig. 2. The sun altitude relationship of the mean extinction coefficient kd was approximated by
k_d=(0.383+0.0035 h₀) cosec h₀ variety Ko-7,
k_d=(0.445+1.22×10^-4h₀^1.69) cosec h₀ variety Ko-1.
The difference in the sun altitude dependence of k_d between two varieties of the crop seems to be due to difference in the orientation function of leaves (see Table 1 and Fig. 1).
The mean extinction coefficient k_d decreased sharply with sun altitude from about 2 for the sun altitude of 5-10°to about 0.6 for the sun altitude of 60°(see Fig. 4), while the value of G_L increased with sun altitude. This is because of rapid decrease in the optical thickness of the canopy (cosec h₀·F_t, where F_t is the leaf area index). Comparing these results it is known that the sun altitude dependence of the mean extinction coefficient for the corn canopy coincides well with that for a canopy of leaves with inclination angles of 40-50°.
The leaf area exposed to the direct solar radiation was evaluated by making use of the data of penetration of the direct solar radiation and the leaf area density within the canopy. Percentage of the sunlit leaf area index to the leaf area index was found to be related to both the growing stage of crop and sun altitude. When the sun was higher the percentage decreased considerably

View full abstract