In view of the radiative heat transfer, the temperature of the plastic film house or tunnel was studied.
At night and under a clear sky, the long wave radiation budget on the outside surface of the film qf′ was expressed by equations (7) and (15) with emissivity, transmissivity and reflectivity of films and the form of the house or tunnel, and that on the floor surface qs by equation (8). By use of these equations. the followings become clear. Generally, in the polyethylene film house or tunnel, temperature of floor surface< inside air temperature<film temperature<outside air temperature, and in the vinyl chloride film house, temperature of floor surface>inside air temperature>film temperature and outside air temperature >film temperature. The difference in air temperatures in and out the plastic house is determined by heat transfer from outside air to film surfaces and heat conduction in soil.

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With opening and closing the window of a plastic house, the air temperature in and out the house and the soil surface temperature in the house were measured. Then, the following results were obtained from these data.
a) Under the rain weather, the heat transfer coefficient of soil surface in the house was 1.7Kcal/m²h°C for the convection of sensitive heat.
b) The heat transfer coefficient of the house was 2.8Kcal/m²h°C.
c) The equation to get the ventilation frequency was obtained by thermodynamic method. By use of this equation an eqation to give the air temperature in the house from the air temperature out the house and the soil surface temperature in the house was obtained. The values calculated by this equation were near the measured ones.

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Efficts of straw mulch on heat balance items are studied by comparing micrometeorological data of an unmuched plot to those of a mulched plot of 3kg per 3.3m². The heat storage in the straw was negligible and the mulching caused a higher value of albedo and a greater upward flux of sensible heat than the unmulched plot. Thus the mulching reduced the soil heat and the latent heat fluxes. The albedo of mulch reached the maximum at an amount of 2kg to 3kg per 3.3m², But the soil heat and the latent heat fluxes decreased with increasing amount of straw applied. In conclusion, the main effect of straw mulch is to increase considerably the sensifle heat flux at the expense of other items of heat balamce.

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It was previously reported by the authors that water saving irrrigation is very effective in preventing cold-water damage to paddy rice. The irrigation control, however, does not always seem to be available when the air temperature is lower than the water temperature of an irrigation channel and when a long spell of drought continues. Such climatic conditions will be detailed with a view to finding out when and where water saving irrigation works most effectively.
From the results of the statistical analysis on the climatic data of the Tohoku District during the past twenty to forty years, the following were obtained: The mean minimum temperature during five-day period, 12.3°C, and the rainfall during ten-day period 40mm and less, are considered as the climatic limit on water saving irrigation.
Judging from the temperature limit, the application areas of water saving irrigation program are presumed to cover all the cold-watered paddy fields in the southern parts of the Tohoku District and the cold-watered paddy fields in the plains of the northern Tohoku District.
The effective application term on water saving irrigation generally comes after June 15 everywhere. Prior to that time the irrigation is feared to affect the growth of rice plant on account of high frequency of low temperature.
According to our observation during the past ten years, the mean daily amount of the evapotranspiration in the paddy field was 3.1mm in June and 3.5mm in July. As the effective rainfall is considered to be 70 to 80 percent of each rainfall, the rainfall of 40mm and less during ten-day period will cause the paddy soil to be gradually dried up.
The frequency of an effective no-rain-day (included a day with rainfall of 1.4mm and less) also acted as other indicator of drought. By checking the areas where the rainafell is less than 40mm in ten-day period and the no-rain-day frequency shows more than 70 percent, it was found out that drought visits the northeastern parts of the prefecture in mid June.
Thus, the rainfall of ten-day period, 40mm, and the frequency of an effective no-rain-day, 70 percent, may be considered as the drying index on water saving irrigation.
It may be concluded that the reading of the normals of the climatic data will tell us when and where water saving irrigation program will succeeded.

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This paper describes the influence of the microclimate of a leaf and the stomatal exchange velocity (D_s) on the sharing of net radiation between sensible and latent heat. Providing that a change in heat storage in the leaf and the energy fixed in photosynthesis are both nil, foliage Bowen ratio (β_f) is expressed as follows:
β_f1=(1+D_f/D_s)(φ_a+d/ΔT_f1)^-1, case 1
and β_f2=0.5(1+D_f/D_s)(φ_a+d/ΔT_f2)^-1, case 2
where D_f is the foliage exchange velocity (or leaf-air transfer coefficient) between the leaf surface and the surrounding air, φ_a the slope (mmHg/°C) at air temperature of the saturation vapour pressure vs. temperature curve, d the saturation deficit (mmHg) and ΔT_f the difference in temperature between leaf and air.
From the above equations, it is seen that for daytime conditions (larger positive ΔT_f), increasing D_f and decreasing D_s lead to increasing the foliage Bowen ratio. The above relations indicate also that the value of Bowen ratio for the leaf of case 1 is twice as much as that for the leaf of case 2. A hyperbolic relation between stomatal exchange velocity and radiation flux was used in model computations. As can be seen in Fig. 1, the value of foliage Bowen ratio increases or decreases with (1+D_f/D_s), depending on the sign of the temperature difference.
Fig. 2 shows that the dependence of the total latent heat transfer from the leaf on net radiation (S_f) is largely affected by relative humidity in the air. In a relatively dry air, the percentage of the latent heat flux to net radiation decreases gradually with increasing net radiation. This result was found to be in good agreement with results obtained in a corn field (UCHIJIMA, UDAGAWA et al. 1969). The percentage decreases with increasing relative humidity in the air and becomes independent of net radiation in a saturated air. Fig. 3 indicates the increase in foliage Bowen ration with relative humidity in the air. This fact is due to the suppression of transpiration by increase in humidity.
The following equation is derived to relate the relative humidity at the leaf surface (foliage relative humidity R_f) to the microclimate of the leaf and the stomatal exchange velocity.
R_f=D_s/D_f+D_s[1+D_f/D_sR_a{1+φ_aΔT_f/e(T_a)}^-1],
where R_a is the relative humidity in the air and e(T_a) the saturation vapour pressure (mmHg) at the air temperature. Curves in Fig. 4 were calculated for leaves of case 2 in a canopy where the air temperature was assumed to be 25°C and the foliage exhange velocity 0.5 and 1.0cm/sec, respectively. The decrease of the foliage relative humidity in a range of net radiation less than 0.15ly/min is thought to be caused by the closure of stomata due to low radiation intensity. In a range of net radiation higher than about 0.15ly/min, the foliage relative humidity decreases monotonically with increasing net radiation. In a sufficiently moist air (R_a=90-100%), the foliage relative humidity is 65 to 95 per cent, always less than that in the surrounding air. The foliage relative humidity of the leaf is 55 to 70 per cent, in relatively dry air (R_a=50%) showing that the foliage humdity is higher than that in the air.
In a middle range of the relative humidity of the air (R_a=60-80%), the foliage relative humidity is greater or less than or equal to that in the air, depending upon the value of net radiation. Results obtained from heat balance analysis o

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On the case that the weight of plant is the function of the height of plant, the author considers of the linear oscillatory behaviour of it in turbulent wind. As power spectral density of response at the point of A is represented by the equation (2.1), the problem to solve is identical to get frequency response function of plant. We get f.r.f. as equation (2.14), (2.15) or (2.16), corresponding on end conditions, from the knowledge of mechanics of materials.
Tracing the process above, the answer is available.

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