The infrared instrument designed to measure simultaneous fluctuations of atmospheric carbon dioxide and water vapor is described. The biggest advantage of the instrument is its simplicity in opto-mechanical system and digital performance in electronics. The noise of the instrument is 0.8ppm for carbon dioxide measurement and 0.02g/kg for water vapor measurement, and the zero drift of the instrument is about 1ppm and 0.03g/kg per an hour. A field test shows that the present instrument is promising for flux measurements of carbon dioxide and water vapor by the eddy correlation technique in conjunction with a sonic anemometer.

View full abstract

In the western parts of Japan, there are frequent risks of frost damage on several crops such as tea plants, vine and others in the late spring. Experimental studies on protection of plants from the cold by sprinkling method utilizing latent heat of solidification were carried out to make establish practical application methods for the sake of saving water consumption.
The main purpose of the experiments is to find the lowest value of effective sprinkling intensity under several air temperature conditions. Through discussions on the fitness of spray catching ratio, the experimental results were examined with the theoretical values by Niemann's and by the author's.
Some results found in the experiments at cold night with radiative cooling are summarized as follows:
1) Temperature of iced leaf under sprinkling could not increase up to 0°C under both conditions of lower air temperatures and smaller sprinkling intensity. There were clearly critical point of sprinkling intensity, which could maintain leaf temperature around 0°C. These points which are defined as the lowest value of effective sprinkling intensity were also changed with surrounding air temperatures. They became larger as air temperatures became lower. The relations between them was a linear one (Fig. 3.). Having compared the measured values with the theoretical values in their tendencies in the graph, it was found that the Niemann's one differed from the actual one especially in the lower temperature range but the author's one agree well throughout the giving range of temperature.
2) The spray catching ratio measured using grouped branches with leaves of cranberry tree (Viburnum awabuki K. Koch) showed almost constant values in the range from 0.1 to 4.6mm·hr^-1 of sprinkling intensity and was about 0.29 on average (Fig. 4.). The theoretical values by Niemann's method changed from 0.27 (at O°C) to 0.36 (at -4°C). On the other hand, the author's one was 0.27 (0--4°C), which was more close value to the experimental one.
3) The fall-off of leaf temperature after 20 minutes of sprinkling-off changed proportionally to the initial leaf temperature, when air temperatures were -3.0--5.8°C. They became larger as initial leaf temperature became higher (nearly equal to 0°C). These relations were also changed parallely with air temperatures, that is, the fall-off of leaves temperatures became large as lowering of air temperatures.
4) After re-sprinkling, the iced leaf temperature which was lowered to around air temperature began to increase showing the shape of saturation curve. The larger the sprinkling intensity was, the shorter the required time to make plant body temperature 0°C was. But in the case of smaller intensity of sprinkling, the required time became longer exponentially.

View full abstract

The horizontal variations of turbulent characteristics were obtained where the 2 and 3 successive windbreak nets (net density 50% and net height 50cm) were set with each distance of 20H (distance expressed in a multiple of net height, negative sign denoting the windward and positive leeward).
The changing pattern of each turbulent element in the case of successive nets is basically similar to that in the case of single net, however, it is recognized that the effects of windbreak net by its succession generally added to the turbulent characteristics of relative mean wind speed (u_r), turbulent intensity (σ/u), skewness (Sk), kurtosis (Ku), turbulent diffusion coefficient (K), energy dissipation rate (ε), smallest eddy (λ) and normalized peak frequency of power spectral density (n_pz/u), particularly, leveled up and down the standards of λ and ε, respectively. As the effect of successive windbreak net for Sk and Ku are just found near the nets, it seems that the changing pattern is independent on each other.
On the other hand, the turbulent elements that the addition of net effect was not recognized and that the tendency of variation was not clear, were upward-downward wind (w/u) and characteristic time scale (T), respectively.
For the successive net interval of 40H, a turbulent characteristic shows an independent variation, and the variation pattern is almost same as that by a single net. Moreover, for the interval of 20H, the addition of successive net effect is considerably appeared as mentioned above. Considering the various conditions, the successive net interval of about 30H is appropriate for a general crop as a prevention of wind damage. When once a wind damage happens to a fruit tree and vegetable, they suffer a severe injury, and it takes a long time to recover the damage. It is necessary to apply the minimum wind speed area as far as possible, i.e., the interval of 10 to 15H. On the contrary in such a net at a paddy field, as the warmed water was moved to the leeward area of the field and the water temperature of a whole field was increased, the interval of net is efficient to be 40H.

View full abstract

The properties of plastic film affect greenhouse environments and the growth of crops. Recently, fog formation has been a problem in plastic greenhouses. Because an environment of high humidity plays a very important role in the infection of greenhouse crops. The relationship between fog formation in plastic greenhouses and the properties of plastic film was reported in a previous paper.
In this experiment, the following items were investigated for the properties of plastic film which are related to fog formation.
1) Relationship between adhesive force and some other properties for some plastic films (Table 1).
2) Dependence of temperature for adhesive force, and deterioration of adhesive force after some days of use.
The properties which are related to fog formation: volume of water which flows down on the film of roof, volume of initial condensed water on the film for 3 minutes, and decreased ratio of transmittance for longwave radiation between dry film and wet film, were measured. The results are summarized as follows.
1) Water volume which flowed down and condensed on the film were directly proportional to adhesive force, which is expressed as work of adhesion (Figs. 1 and 2).
2) The maximum volume of initial condensed water on the film was 7.8×10^-4g/cm²/3min for D-film (PVC) and the minimum was 5.8×10^-4g/cm²/3min for A-film (PVC).
3) Difference of both maximum and minimum volume was calculated at 4.4g/min per one meter of the greenhouse (width 3.5m, height 2.5m) which was used in this experiment.
4) The maximum volume of water which flowed down on the film of roof was 14.5×10^-3g/cm²/night for G-film (PVC).
5) The minimum volume of water was 8.2×10^-3g/cm²/night for c-film (PVC).
6) Difference of both maximum and minimum volume was calculated at 0.4g/min per one meter of the greenhouse.
It is presumed from the above results that the volume of initial condensed water largely affects fog formation in greenhouses, rather than the volume of flowing water on the film at night.
Three types of film (namely X, Y and Z) were examined to determine the dependence of temperature for adhesive force, and deterioration of adhesive force after some days of use. X-film has similar quality of a-film and Y-film, has similar quality of b-film. The results are summarized as follows.
1) X-film had the largest work of adhesion below 20°C when film is new (Fig. 4), yet after 170 days it became the smallest except 5°C (Fig. 5).
2) Work of adhesion for these three types of film decreased after some days of use.
3) Decrease rate for X-film was the largest among these film types (Fig. 6).
4) Many cases of high humidity and dense fog were measured from 26 May to 9 June in the greenhouses covered with Y and Z-film; however, there were many cases of low humidity from 4 Nov. to 22 Nov. compared with the greenhouse covered with X-film (Fig. 7).
It became clear that X-film has strong adhesive force in low temperature and when film is new. The dense fog in the greenhouses covered with Y and Z-film is caused by the difference of adhesive force between Y&Z-film and X-film at low temperature and when film is new.

View full abstract

In the present communication, a theoretical analysis of air flow near windbreak structure was carried out to obtain some information about the optimal conditions of structure to be constructed, applying the computor program already proposed (Takahashi, 1982). Two parameters, shelter density (D) and Reynolds number (Re), and a decreasing rate of wind speed, which generally characterize the patterns of air flow, were examined in detail for analysis. The results obtained are summarized as follows:
1) The wind flow pattern on both sides of structure varied depending on the values of Re: the decreasing effect of wind speed is maximum in the range of 25<Re<83, indicating that the Re value is significant in this range.
2) With higher Re values (Re>85), the flow pattern clearly depended on flow time as characterized by the following observations. At first, a regular oscillatory motion arose behind windbreak structure and then induced the formation of vortices on both sides of structure. Next, the vortices gradually moved towards downstream and then it was mixed with main flow. The flow finally meandered at a slow or high speed, the weak and strong flows and their appearance regions are characterized according to the change of Re.
3) When a simulation model was set using various values of D(=100, 90, 80, 70, 60 and 50%) to see the relationship between D and a reduction of wind flow speed, we found that with lower Re values (Fig. 5) the decreasing rate of wind increased parallel to D value, while in the case of higher Re values (Fig. 6), the D value of 60% was effective for a decrease in flow speed. These phenomena are explained with the formation of vortices or the meandering flow results with the relation between the vortices and main flow.
From the data obtained, we conclude that both parameters applied for analysis of air flow are closely related to the wind pattern arising near windbreak structure and offer the optimal conditions for structure.

View full abstract

The height distributions and time variations of airborne pollens were observed at six heights within and above plant canopies, using Durham samplers, in 1983. The flowering seasons of a wheat was the period from the latter part of April to the first part of May and that of a rice was the period from the latter part of August to the first part of September. The mean heights of both plants were about 95cm. The results are summarized as follows.
(1) A lot of wheat pollens was released in the period from 27 to 29 in April. Most of the remainder were probably lost due to the precipitation and strong winds on April, 29.
(2) The pollens of a wheat were always released in the daytime and were hardly sampled in the period from late evening to night.
(3) The number of sampled pollens of a pine tree increased in the strong wind conditions, irrespective of daytime and nighttime.
(4) The pollens decreased in number during and just after precipitation.
(5) The number of sampled wheat pollens was maximum just above a plant canopy and decreased rapidly above and within plant canopy. On the other hand, that of pine pollens was great above plant canopy and decreased within plant canopy.
(6) The number of sampled rice pollens was maximum in the middle layer of plant canopy. It decreased rapidly above plant canopy and was about 1/10 of the maximum value at the height of 2m.
The above-mentioned results are still insufficient for further discussions of movement of airborne pollens within and above plant canopies because of the limited observational data and disadvantage of Durham sampler. The improvement of sampling techniques and accumulation of observational data remains as future problems.

View full abstract

The problems are whether evapotranspiration (ET) from paddy field would be affected by growth stage and by rice varieties, and whether the radiation method and Priestley-Taylor method for estimating ET would be applicable to paddy field.
ET was measured with microlysimeter (Tomar and O'Toole, 1980A) at the eight test plots (N1-N8) in which cultivar “Nipponbare” (Japonica rice) was grown under eight different cropping seasons, and at the two plots (K5 and R5) in which cultivars “Milyang 23” (Japonica-Indica cross variety) and “IR-36” (Indica rice) were grown under the ordinary cropping season (see Horie and Sakuratani, 1985, Table 1). Three stainless pans (30cm long, 20cm wide and 60cm deep) were installed in the center part of the each plot: the two with the hills of rice plant and the other without crop were used as evapotranspirometer and evaporimeter, respectively. ET and transpiration (T) from each plot were determined, respectively, by averaging the values of ET from the two pans, and by subtracting the evaporation (E) from the ET. Meteorological data were also collected.
In each cropping season of “Nipponbare” rice, the E at the early growth stage in which the leaf area index (LAI) was small, was comparable to the ET at the maximum LAI stage (Fig. 2A). Thus, there was no appreciable difference in ET between the two stages. This also caused the noticeable increase of total E for entire growing periods in the plots of the earlier cropping seasons such as N1 and N2 in which the initial growth was delayed by lower air temperature (Table 1). The mean value of daily ET ranged between 3.5 and 4.2mm day^-1 for the eight cropping seasons, averaging 4.0mm day^-1.
The ratio of ET to reference ET (ETR) calculated from modified Penman method (Doorenbos and Pruitt, 1977) was fairly constant throughout the main growth period except mid-September to October and averaged 1.05 for all the cropping season (Fig. 2B). The overestimate in the ET in the fall seemed to be owing to the enrichment of ET by advective energy and to the underestimate in the ETR. On the other hand, the ET/ETR for “Milyang 23” and “IR-36” tended to increase slightly around the heading stage (Fig. 4). These varieties also tended to show higher T than “Nipponbare” under the LAI above 2.0 and high radiation conditions (Fig. 5). These results suggested that crop factor such as canopy resistance is somewhat important in controlling ET of Indica type rice, whereas not so important for Japonica rice.
The variation of the daily value of a in the radiation method (Eq. 7) was relatively small throughout the main growth period (Fig. 6). The linear regression technique for all the cropping seasons yielded a=0.88, and five-day ET was estimated with high correlation coefficient (r=0.912).
The daily value of α in Priestley-Taylor method (Eq. 8) greatly fluctuated over the growing season (Fig. 6). Apparently, this variation of α was attributed to that of daily net radiation caused by long wave radiation exchange at nighttime. Priestley-Taylor method seemed to be less effective in estimating ET of paddy field in Japan when daily values of net radiation are used.

View full abstract