In the Tohoku district, the cooler region in Japan, the cultivatable period of rice plants is shorter, and moreover, the extremely cool weathers have often occured during the important growth periods. Therefore, these periods are necessary to fit climatically in safe time. Such agro-climatological studies for estimating the rice cultivation period have recently developed in Japan and the methods which set the heading to a center of the plan have been established. In earlier studies the earliest and the latest dates of the safe cultivation period were established on the basis of seasonal variation curve of air temperature or of accumulated air temperature usually by the critical temperature free from cool damage, but they have not discussed the products from the quantitative point of view. Therefore, it was difficult to estimate physiologically of economically the most suitable cultivation period considering the management of a farm. For the purpose of settling this difficulties, it is necessary to elucidate the relationships between the changes of climatic conditions and of yield, corresponding to the movement of the important growth periods.
The Authors have found the method for estimating the course of yield index corresponding to the heading by the application of such assumptive decreasing scales of rice yield based on low air temperature at the important periods as Fig. 1. These scales were proposed by Abe et al. (1964) in connection with the study (1960-1961) for estimating the damage by cool weather conditions on rice production.
If the decreasing rates of yields by low temperature at three important periods of rice plants such as the reduction division period, the heading and ripening periods in case of heading on the date i in the year j, are designated by (R₁)_ij, (R₂)_ij and (R₃)_ij respectively, the yield index Y_ij will be as follows.
Y_ij=100(1-(R₁)_ij)(1-(R₂)_ij)(1-(R₃)_ij)
(1)
The mean yield index for n years on a specific date i, Y_i will be written
Y_i=∑nj=1Y_ij/n (2)
From Eqs. (1) and (2), yield index in case of heading on a spontaneous date can be calculated and consequently, the course of yield indexes is drawn in Fig. 2. For instance, the yield indexes and their course calculated from daily air temperature from 1937 to 1963 at the Fujisaka Farm are shown in Fig. 2 and Table 1.
Taking the scale of a farm and working efficiency into consideration, if Y_p is the planned level of yield index per unit area, the heading period obtaining products more than Y_p is the term between H_c and H_l, the crossings of the curve of yield index to Y_p-line, as shown in Fig. 3. But the heading time is apt to delay by the low temperature before them. Therefore, when the number of days of probable lateness, Ll is calculated by the other method, the date Hp, Ll days before H_l is obtained as the planning latest heading date, and the period from H_c to H_p, L_p is obtained as the planning safe heading period.

View full abstract

There are many climatic Factors, that have some influence upon the soil moisture; Precipitation, evaporation, transpiration, temperature, wind velocity and so on. Under them the period without precipitation is one of the most powerful factors, that work on the soil moisture to fall, and the anotner one is the plant covering. It has a same effect, if the earth's surface expands to the rhizosphere of plants. If the earth's surface has dryed up, it seems to evaporate not more. The soil moisture remains unchanged. In such condition the plants transpirate increasingly, because of the high radiation-balance, until the rhizosphere runs dry. Therefore the period without precipitation is the best factor for the estimating the days to need irrigation.

View full abstract

In winter of 1963, heavy snow fall by unusual cold weather resulted in considerable destroy to trellis and shoots of fruit tree. An analysis was made to clarify the relation of snow depth to mechanical damage of trellis and shoots from the data of this investigation. The results obtained are as follows;
(1) These data show that a snow depth near 150cm was critical for breaking trellis and shoot of fruit tree.
(2) Commercial production of fruit tree are practiced in our country in the regions where snow depth of 150cm occurs every 10 years or more longer intervals as shown in Figure 3.
(3) It would be desirable to culture fruit tree at meteorologically favorable places where the snow depth of 150cm occures every 10 years or more longer intervals.

View full abstract

It should be noticed that when we grow plants in a closed room like a glasshouse, their environment is quite different from that out of doors. Regarding the concentration of carbon dioxide in the air, it is increased in the glasshouse to get more harvest in recent experiments. But most glasshouses and phytotrons in this counntry maintatin the supply of carbon dioxide by ventilation. A study on this matter was made earlier by MORRIS et al. (1954). Since then, this problem has not been developed further. MORSE and EVANS (1962) designed the CSIRO Phytotron using MORRIS' hypothetical minimum ventilation rate. Furthermore, MORSE (1963) calculated the ventilation rate of the growth cabinet, assuming that the plant net assimilation rate was constant in spite of the large decrease in carbon dioxide concentration in the air. In the present paper, our study is to improve the methods used by MORRIS and MORSE, and to demonstrate the close relationship between the plant net assimilation rate and the ventilation rate in wide range of values of parameters. We assume that the plant net assimilation rate has a linear relation with the concentration of carbon dioxide in the air, i. e.,
a=C-C_c/C₀-C_c-a₀, C≥C_c,
where a is the rate of net assimilation in the glasshouse per unit area per unit time (g/m²hr), C is the concentration of carbon dioxide in the glasshouse per unit volume (g/m³), C_c is that of compensation point (g/m³), C₀ is that out of doors (g/m³), and a₀ is the rate of net assimilation out of doors (g/m²hr). In Fig. 1, the line (A) is used by us, and the other (B) was shown by Morris et al. We also assume that the concentration of carbon dioxide in the atmosphere near the ground is constant in the daytime, the molecule of carbon dioxide in the glasshouse is always mixed uniformly, the influence of the temperature coefficients of respiration and assimilation are small, and the concentration of carbon dioxide is the limiting factor of plant photosynthesis. In this paper we shall confine the discussion to the simple problem of the soil free carbon dioxide in the glasshuose.
We calculated the efficiency of plant assimilation rate in two ways. One is
a/a₀=m·z+2m/m·z+2m+1,
where m is c_e·v/a₀·s, z is ventilation rate (1/h), v is the glasshouse air volume (m³), C_e is C₀-C_c, s is growing area (m²), and a is (a₀+a_i)/2. This equation was solved using a linear approximation in the change of carbon dioxide concentration. The other is the strict solution of this problem, that is, a_i/a₀=1-a₀/c_e·j·z+a₀{1-exp[-(z+a₀/c_e·j)t]} where j is V/S, t is time, a_i is the plant net assimilation rate in the glasshouse. If a₀ and C_e are fixed at 5.0g/m²hr (MORSE and EVANS, 1962) and 0.394g/m³ (Egle 1951) respectively, the ratio a_j/a₀ is the function of t with parameters i and z. Suppose the obtainable values of j are from 1 to 15 and that of z are from 1 to 100, the computation of this equation is very complicated, Taking t from 0.05 to 0.5 at the interval of 0.05 and from 0.5 to 5 at the interval of 0.5, j as integer, and z from 1 to 20 continuously, 25, 30, 40, 50 and 100, we calculated this equation using the electric computer at the Computation Centre, University of Tokyo. Some of the typical exmples are shown in Fig. 3.

View full abstract

In recent years, the chamber method in determining photosynthesis and transpiration of crops has become in common use among the crop scientist, and a number of studies have been published of the amount of transpiration and photosynthesis of crops. But little attention has been paid into the control of microclimatic environments in a chamber. In this paper, the relationship between microclimatic conditions and the ventilation rate was numerically studied on the basis of heat balance, water vapor and carbon dioxide balance techniques. Vertical profiles of several microclimatic elements within a plant canopy in the chamber were also studied by the micrometeorological method.
As can be seen in Eq. (5), the difference in temperature between in and out the chamber is determined in terms of total heat transfer coefficient h_t, advectional heat transfer coefficient h_ad, net radiant energy _iS₀, apparent vapor deficit {r·e(T_a)-₀e_a}, coefficient of keeping warm R=A_f/A_w and relative humidity r in the chamber. The results obtained from Eq. (5) is presented in Fig. 1. It was found that the value of water vapor pressure in the chamber is closely related to net radiant energy, Bowen ratio and ventilating rate per unit area of the chamber floor. The relationship between ventilating rate and water vapor pressure in the chamber is shown in Fig. 1.
Carbon dioxide concentration in the chamber was found to be determined in terms of total gas exchange coefficient D_t and ventilating rate per unit leaf surface. The result obtained from Eq. (13) is presented in Fig. 1. The value of total gas exchange coefficient for several crops is summarized in. Table 1. The efficiency of photosynthesis of crops in the chamber was evaluated from Eq. (14) and compared with experimental results obtained by MURATA (1961) in Fig. 2. In the range lower than ventila. ting the rate of about 1000cc/leaf cm²hr, the photosynthetic efficiency of crops in the chamber decreased drastically with the decrease of ventilating rate. Fig. 4 illustrates the vertical profiles of relevant quantities within a canopy of crops in the chamber obtained by micrometeorological techniques. A notable result shown in this figure is that the remarkable discrepancy in amount is between foliage Bowen. ratio and ordinary Bowen ratio. This result agreed with that obtained within a corn plant canopy under field conditions.

View full abstract