Fruit cracking in cherry tomato is a serious problem. The percentage of fruit cracking in hydroponic cherry tomato often exceed 20%. In this paper, conditions that induced the fruit cracking were investigated. A reduction method of fruit cracking in NFT system by pumping control for hydroponic solution circulation was also reported.
It was revealed with the moisture pathway experiment that the fruit cracking occurred when the fruit swelled with water absorption due to some ill balance of water inflow and outflow of tomato fruit under some conditions. In usual conditions, a volume of water flowing into the fruit from the root might be well balanced with a volume of water flowing out from the fruit through the skin into the atmosphere.
It has been found through measurements of the tomato fruit water potential and the sap flow rate that the NFT cultivated plants responded sensitively to the water status of root zone that varied with pumping schedule for the hydroponic solution circulation. It was also disclosed through the water flow measurements that tomato fruit kept taking up water and responded to the on-off operation of the circulation pump even in the midnight when tomato plants needed much less water.
Through these experiments, it was concluded that the water flow into the fruit could be suppressed by a proper control of off period of circulation pump. The reduction of fruit cracking was accomplished with making the off cycle of pumping longer than the usual one during night. From two replications of the cultivation experiment, the 8 hr of off cycle treatment effectively reduced the percentage of fruit cracking down to as much as 50% compared to the one with the usual pumping cycle.

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Experimental and theoretical investigations were conducted to evaluate the uniformity of cool air discharge along a perforated distribution tube for zone cooling in a greenhouse. The calculated static pressures in the tube agreed well with the experimental results. Air temperature in the tube was calculated by considering a constant overall heat flux through the tube wall along the tube length. A good agreement was obtained between the calculated and measured air temperatures in the tube. The coupled analysis of air flow and heat transfer was used to simulate the uniformity of cool air discharge for practical input variables. Furthermore, the relationships between the uniformity of cool air discharge and the design parameters of the tube were obtained.

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CELSS (Controlled Ecological Life Support Systems) is to be considered to construct the closed environment for sustaining the life including human beings without any material supply from outside. The water recycling system is a key subsystem of the integrated material recycling system which must be developed to obtain long-term, manned space activity. This paper presents the results of system study for designing water recycling system in which three kinds of membrane filters (UF, RO and TPV) are introduced to purify waste water discharged from men, animals and plants. In addition, the long duration processing tests utilizing artificial urine waste water were conducted to evaluate the appropriateness to adapt these membrane filters.
The following results were obtained: 1) The prototype water recycling system could be controlled and working smoothly. However, the system needed some maintenance of several parts of the equipments for it to operate completely in the given desired period. 2) The removable rate of water from artificial urine was below 60%. 3) The crystal materials namely MgKPO₄⋅6H₂O, Mg₃ (PO₄) ₂⋅4H₂O and CaHPO₄⋅2H₂O which shortened the life time of each filter were found in tank, pipe and filter. 4) The urine removable rate of RO filter was lower than that of commercially sold filters which extracted only NaCl water. In the special case of ammonia which could not be extracted completely even using TPV filter after RO system, it is necessary to develop a new filter that can remove ammonia for a further suitable process.

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Radish seeds were exposed to various cyclically fluctuating magnetic fields with a treatment apparatus of a rotary type disk. The germination percentage, the sprouting percentage and the plant growth were evaluated with the germination test and the solution culture test. The treatment conditions were as follows: the magnetic flux densities exposed to seeds in the germination test were 30, 60 and 120 mT but only 60 mT in the solution culture test; the magnetic polarities faced to seeds were N and S; the rotating and the fixing of seeds; the exposure times were 0, 5 and 15 min in the solution culture test but only 15 min in the germination test.
The germination percentage of seeds treated by the cyclic magnetic fields indicated no significant difference from that for the control. However, the root length of the plants significantly increased than that for the control in the germination test. Particularly, under the condition exposed to the S-pole and to the fluctuating magnetic field with the magnetic flux density of 60 mT, the root length was most effectively increased.
In the solution culture test, the sprouting percentage was considerably progressed in the cyclic magnetic fields. Especially, the exposure to the S-pole and to the fluctuating magnetic field of 120 mT indicated the best result in the sprouting percentage. However, the subsequent plant growth and harvests had no significant difference from those for the control.
In general, when radish seeds were exposed to a cyclically fluctuating magnetic field and to the most desirable magnetic flux density, the early root length was increased, consequently, the sprouting percentage of plant in the solution culture test was more processed than that for the control.

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It has been said that response of plants to environment is irregular and complicated. We have intuitively attributed the reason to complexity of living systems. In nonlinear systems, however, complex phenomena can be generated by simple rules. They are called chaos. So we examined whether irregular response of photosynthetic rate and growth rate are chaos. To measure accurately as many data as possible, six environmental factors were controlled in a small growth chamber. Air temperature, humidity, CO₂ concentration and air pressure were changed by a computer while PAR (photosynthetically active radiation) and wind speed were kept constant. Photosynthetic rate and growth rate (measured by the diameter of the stem) were recorded as a function of time and chaotic nature of the time series data were analyzed. By calculating the correlation dimension, response of photosynthetic rate was identified as chaos. The correlation dimension of photosynthetic rate was 2.7±0.4 and that of growth rate was larger than -4.5.
Moreover to examine the chaotic nature of photosynthetic rate, predictions by four different models were compared. Two of the models are nonlinear models developed with neural networks and two are linear regression models. The models predict photosynthetic rate using four different environmental factors. One linear model and one nonlinear model included a factor of delay, which is represented by a variable of actual photosynthetic rate in one past step. Only the nonlinear model which included the factor of delay could predict unknown test samples well. No other models generated irregular patterns of photosynthetic rate. Therefore we concluded that photosynthetic rate behaves chaotically. Although we cannot forecast plants' response far into the future because of the chaotic nature, we can expect to control the growth by very few energy based on orbital instability of chaos.

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The present experiment was undertaken in order to clarify the effect of application of ammonium nitrogen to the nutrient solution on the growth, yield, photosynthesis, chlorophyll content and root activity of pepper plant (Capsicum annuum L.) at day temperatures of 25, 30 and 35°C.
Cultivar‘Nokkwang’ used in this experiment showed the highest growth and yield at 30°C, indicating that the optimum day temperature should be controlled at this level.
At the day temperatures of 25 and 30°C, NH_4-N application at the ratio of 20% against total applied nitrogen resulted in the stable acidity of the solution. Further beneficial effects of NH_4-N application resulted in higher fresh weights of leaf and stem, increases in leaf area and root respiration, as well as higher fruit number and yield. Chlorophyll content in the leaf increased with NH_4-N application at all day temperature.
At the day temperature of 35°C, however, NH_4-N application resulted in decreased plant growth and yield. Results obtained indicate that the plant grown in summer at high temperature should be applied with NH_4-N free solution, and that NH_4-N should be applied in order to encourage the plant growth and yield in the other seasons.

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Infrared rays contained in the solar radiation are well known to contribute little to photosynthesis of plants and convert easily into heat in a material absorbed. Thus, the exclusion of infrared rays with covering materials of greenhouses is expected to be an effective method to enable greenhouse culture during a high temperature period and cut down the cooling load of greenhouses.
In this study, the thermal characteristics of a greenhouse covered with a new selective absorber of infrared rays which has been commercialized were measured from summer to autumn. The following results were obtained by comparisons of these characteristics with those measured in the same scale glasshouse during the same period.
1) The effect of the present covering material on suppression of temperature rise in a greenhouse with all windows closed was small for inside air but considerable for soil surface of floor.
2) The reason for the small effect on inside air temperature was that over-all heat transfer from inside air to outside air was weakened by temperature rise of the covering materials due to absorption of infrared rays.
3) Under the condition of natural ventilation with all windows open, the effect was less for inside air but relatively large for soil surface.
4) The covering material also affected leaf temperature and the effect on suppression of temperature rise in lettuce leaf under solution culture increased with increasing solar radiation.

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Rice plants were grown in artificially illuminated growth cabinets under conditions of ambient CO₂ concentration, 28/23°C, 12-hr day/12-hr night temperatures, and 3 or 300μM phosphorus in a standard nutrient solution with soil. At the 10-leaf stage, atmospheric CO₂ (350 or 700μmol mol^-1) and temperature (28/23 or 28/28°C) were controlled and maintained until the harvest at 40 days after heading. At 28/23°C, the high phosphorus accelerated heading by 2-3 days while the high CO₂ accelerated heading only by one day. Culm and panicle lengths were not affected by high CO₂, but they increased under high phosphorus. Panicle numbers were greater in both high CO₂ and high phosphorus. Panicle weight increased 20 and 40% at low and high phosphorus, respectively, in the high CO₂ treatments without amelioration of the harvest index (ca. 0.5) . In 28/28°C-high CO₂ plot, the heading was accelerated 3-4 days and the plant weight was similar to 28/23°C-high CO₂ plot, but the harvest index was lower (<0.4) than for the 28/23°C-low CO₂ plot, because the dry matter was preferentially partitioned to vegetative parts, especially to roots. At elevated atmospheric CO₂, the phosphorus nutrition is important to increase rice yield. Thus, under the expected climate change due to increased green-house gases, appropriate plant nutrition to control photoassimilate partitioning will be an important practice.

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The present study was undertaken to evaluate the physiological characteristics of strawberry plants‘Nyoho’ affected by the nutrient concentration and NH₄-N ratio to the total N. The treatment was combined two levels of nutrient concentration (EC 0.9, 1.7 mS/cm) and three levels of NH₄-N ratios (10%, 20%, 30%) .
The higher fresh weights were observed in plants with the low nutrient concentration of 30% NH₄-N ratio, and with the high concentration of 20% NH₄-N ratio. The greater total fruit yield was obtained in plants with the low nutrient concentration of 30% NH₄-N ratio as compared with the other plots. The distribution of ¹³C-assimilates to the root decreased in the high nutrient concentration. In the case of the low nutrient concentration, the distribution of assimilates decreased in the terminal cluster and increased in the lateral cluster at the ratio of 30% NH₄-N. The decrease in C-N ratio was observed in plants with the high concentration of 20% or 30% NH₄-N ratio. The potassium content in the root increased in plants with higher nutrient concentration and/or higher NH₄-N ratios. The esculin oxidized in the root increased with increasing NH₄-N ratios in the nutrient solution.
It is concluded that the better plant growth and higher yield were obtained in the plants grown with the low nutrient concentration of 30% NH₄-N ratio. This may be due to increased translocation of assimilates to the root, increased phosphorus and potassium contents in the root, and increased respiration rates in the root.

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