We point out a new composite environmental effect which appears in the neighborhood of limiting values of specific environmental factors for growth. This effect implies the existence of the physiological limitation, and thus the saturation relation of growth against the total effect of environments. Then, there must exist the law of diminishing utility near the extreme values of the latter. It is never preferable that environmental control is carried out in the region of diminishing utility of expensive factors.
Based on this law, we propose the general optimization principle for plant factories which claims that environmental factor with larger cost-performance should have priority of optimization. This principle when applied is expected to improve the payability of totally controlled factories in particular.

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The effects of direct current through a plant or the medium of callus culture on the growth have already been studied, however, the experimental example on the effects of direct current flow to callus cannot be found as yet. Then the current effects on the multiplication of asparagus callus were studied and evaluated when the weak direct current of various amperage and voltage were flowed.
Using the three units of direct current circuit consists of a power supply source with a output voltage of 10 V, many fixed and variable resistors and the three paired platinum wire electrodes contacted with each callus surface, the calli were treated over the range of the applied voltage of 1-5V and the applied amperage of 1-2.5μA i. e. the consumption power of 1-12.5×10^-6 W for seven days during culture. These fresh weights, percentages of multiplication and growth ratios of percentages of multiplication to control were compared with control and were evaluated after twenty days of the untreated and continuous culture.
The results were as follows : any values of treated calli were increased than control with increase of the consumption power except a case of 1V-1μA. Especially, a percentage of multiplication at 5V-2.5μA was increased significantly at 1% level and was about 3.2 times of control, however, a consumption power at this time was only 12.5×10^-6 W. The possibility of stimulation of callus multiplication with the higher voltage and current was suggested.

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An unmanned transport vehicle was developed and tested, which was trackless and guided by more than one ultrasonic sensors, for the purpose of labor saving and automation of hard works in water cultivation greenhouses.
The vehicle is a motor-driven four wheel car, which has a four-wheel steering mechanism to steer front wheels by motor and rear wheels in an opposite direction through a link rod, each of two rear wheels being driven by a geared motor of 120W.
In the traveling test, it was established that steering of the vehicle can be controlled by a simple proportional method with the yawing angle of the vehicle taken into consideration;the vehicle can be turned in a narrow area at the end of bed using the opposite phase four-wheel steering mechanism, and; its traveling path can be detected and controlled by marking plates (steel) installed on roads and contactless switches attached to the bottom of vehicle.

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A new type of the nutrient sensor using ISFET (ion-sensitive field-effect transistor) has been investigated. Measuring the ion concentration of a solution in plant growh media (ex. rockwool) is difficult and has not been carried out in practice. The authors anticipated that an ISFET, with its advantages of small size and low output resistance, could be used to measure the ion concentration of such a solution in growth media. In this study, the authors examined the basic characteristics of ISFET-based nutrient sensor probes in rockwool as follows : 1) response characteristics for nitrate ion concentration changes in rockwool, 2) reproducibility of the output when they were inserted into rockwool repeatedly, 3) output dependence on the rockwool water content, 4) output dependence on the distance between the ISFET and a reference electrode, 5) long-term stability of the sensitivity and output baseline in rockwool. These experiments have shown that the sensors have sufficient stability for use in this kind of measurement. The authors have found that ISFETs are able to measure the ion concentrations for a nutrient solution in growth media such as rockwool.

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In this study, air cooling in the zone only around plants in greenhouse in the daytime in summer was investigated.
Two types of air cooling systems were constructed in a greenhouse in Ehime University. One was the system which used cold water and water-air heat exchanger (cold water cooling system), and the other was the system which utilized heat of vaporization of fog (fog cooling system). Schematic diagrams of these systems are shown in Fig. 1 and Fig. 2.
The results of air cooling on a fine day are shown in Fig. 4, Fig. 5 and Fig. 6. Furthermore, Fig. 7 shows the effectiveness of system identification in analysis and control in cold water cooling system.
The effect of environment of above-ground part on occurrence of blossom-end rot of tomato plants was also investigated. The effect of air flow to fruits was also examined using the system shown in Fig. 3. The results are shown in Fig. 8 and Table 1.

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Blossom-end rot of tomato fruits occurred when tomato plants (Lycopersicon esculentum Mill. cv. Momotaro) were grown in Ca-rich nutrient solution by using the nutrient film technique. Concentrations of Ca ions were high in both stems and leaves of plants yielding fruits having blossom-end rot. However, Ca concentrations in fruits suffering from blossom-end rot were significantly lower than normal fruits. This indicates that Ca ion diffusion from stems to fruits was physiologically inhibited, resulting in blossom-end rot in fruits. This phenomenon was associated with reduction of photosynthesis. Because plants yielding blossom-end rot absorbed significantly higher concentrations of Mn and Zn ions than healthy plants, it may be possible that enzymes related to calcium transport and photosynthesis might be inhibited with the higher concentrations of heavy metal ions.

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