A new technique for cultivating sweet potatoes (I pomoea batatas L.) in a solution culture in order to make root tuber formation in the air space of a culture box was developed. The effects of rockwool slab in the medium, and also the composition and supplying method of nutrient solution were examined to maximize root tuber yield. This technique was also applied to compare the yield differences among cultivers. Cultiver‘Kokei No. 14, ’‘Kotobuki’and‘Narutokintoki’were used in this experiment. The plastic culture box (W 400×D 700×H 320 mm) was separated into two parts, i.e., the solution layer which was set in the rockwool slab of 2 cm in thickness and the air space of about 30 cm.
Seedlings were provisionally planted in sand medium for about twenty days before trans-planting until the root length was elongated to 30-40 cm so that the root reached the solution layer when it was planted at the top of the culture box. Absorbing root was grown in the solution layer, and root tuber was tuberized in the air space. The results of the experiment are as follows.
1) From the experiment on the relation between root tuberization and medium composition, yield of root tuber was increased by 1.5 times when standard solution (Kasugai's solu-tion-B) were used in the rockwool slab compared to the case without the rockwool slab.
2) From the experiment on the relation between the root tuberization and the composition of the culture solution, it was found that root tuberization was improved and the yield was increased by 1.45 times when the concentration of NH₄N0₃ in Kasugai's solution-B was doubled for 30 days after transplanting, and subsequently, concentrations of KCl and KH₂PO₄ were doubled until the harvest.
3) Large yield, 1.350, 1.350, 1700 g/plant for‘Kokei No. 14, ’‘kotobuki’and ‘Naruto-kintoki’respectively, indicated that the solution culture is suitable for various cultivers of sweet potatoes.

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The weight of harvested fruits, and the contents of total soluble solids and phenolic compounds were determined in four peach cultivars (Prunus persica BATSCH) planted in plastic containers grown under different conditions of soil moisture and air temperature.
Using the peach trees, cv.‘Takei Hakuho’grafted on P. persica, and cv.‘Sanyo Suimitsu’grafted on P. persica or P. tomentosa THUNB., soil moisture tension (pF) was maintained for each stage of fruit growth such as an early period (Stage 1), a stone-hardening period (Stage 2), and a maturation period (Stage 3) at 2.3 to 2.7 by withdrawing water. Whereas in the control pF was maintained at 1.0 to 1.5 throughout experiments. Later time of the drought treatments resulted in later maturation of fruits in either cultivar. In both‘Takei Hakuho, ’and‘Sanyo Suimitsu’grafted on P. tomentosa, the smallest fruit and the highest content of phenolic compound in the fruit were observed in the drought plot during the Stage 3. In ‘anyo Suimitsu’grafted on P. persica, the content of phenolic compound was high not only in the drought plot during the Stage 3, but also in the control one.
When peach trees, cv.‘Saotome’and‘Chikuma’grafted on P. persica were grown under four different air temperatures throughout Stages 2 and 3, the content of phenolic compound in the fruit was higher in the plots of 15°C and 20°C than in those of 30°C and the control, in which plants were grown outdoors throughout experiments. In‘Sanyo Suimitsu’ peach trees on P. persica grown at 20°C and 30°C of air temperatures during Stages 2 or 3, the content of phenolic compound was higher at 20°C than at 30°C in either stage, and it was also higher in the treatments of Stage 3 than in those of Stage 2 for both temperatures. Regardless of cultivar, at any plot treated with constant air temperatures of 15°C, 20°C, and 30°C, fruit weight was small, compared to the control. Average air temperature outdoors was 22.8°C or higher throughout the treatments.
From these results, it is considered that soil drought and low air temperature during the Stage 3 of fruit growth is closely related to the occurrence of astringency in peach fruits.

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The effect of CO₂ enrichment and high solar radiation on the growth of potato (Solarium tuberosum L. cv. Benimaru) plantlets in the direct ex-vitro rooting method was examined. Explants of micropropagated shoots, single node cuttings each with a leaf, were inserted directry into the rockwool plugs and cultured inside the environmental control units at different intensities of solar radiation under CO₂ non-enriched and CO₂ enriched conditions.
On the 35th day, the fresh and dry weights and the number of leaves of the plantlets under high solar radiation and CO₂ enriched conditions were, respectively, 2.4, 3.1 and 1.7 times greater than those under low solar radiation and CO₂ non-enriched conditions. High solar radiation and CO₂ enrichment promoted the growth and rooting of the plantlets in the direct ex-vitro rooting method.
The fresh and dry weights of the plantlets under high solar radiation and CO₂ enriched conditions in the direct ex-vitro rooting method were greater than those in the conventional method.

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The effects of growing temperatures and day length on flower bud initiation and development were investigated. Three sweet pepper cultivars, ‘California Wonder, ’‘Shin-sakigake’and‘Shishito’were transferred to the phytotron and exposed to temperatures of 15°C, 20°C, 25°C and 30°C at the unfolding time of the cotyledons (Exp. 1) or at the time of flower bud initiation (Exp. 2) . The plants were grown at these temperatures under natural, (short) day and also under long day.
As the growing temperature rose, the number of nodes on the 1st flower bud decreased (except 15°C) . The flower bud was initiated at only 15°C and under long day. Comparing the number of nodes in the three cultivars at the budding, the lowest was 10.9 of ‘Shin-sakigake’ and the others were 11.3 and 14.5 for ‘California Wonder’ and‘Shishito, ’respectively. The higher the growing temperature, the fewer the number of days for the initiation of the 1st flower bud.
The number of days for the initiation of the 1st flower bud decreased more under long day than short day in the three cultivars. The difference of these days under long day and short day was smaller as the growing temperature rose and the flower buds were formed almost at the same time under both day lengths at 30°C. The effect of day length on the number of nodes on the 1st flower bud was not clear. Though the budding of the three cultivars was promoted as the temperature rose, the budding at 25°C and 30°C occurred alsmost simultaneously.
From these results, it is deduced that the 1st flower bud of the three cultivars used is formed earlier and at a lower node as the growing temperature rises. It seems that the 1st flower bud is formed earlier under long day than that of short day but the effects of day length on the number of nodes to the 1st flower bud was not clear.

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This study was carried out in order to analyse the physical and chemical characteristics of rockwool mat as a carrier of nutrient solution in soilless culture. The volume of the solid phase in the mat was very small (about 3%) . The saturated water capacity was 90% or more, and most of the water in the mat was held at a high matric potential (below pF 1.5) . When the water saturation over the mat was above the range of 50%, the water saturation degree in the deep layer (below 1/2 of the 7.5 cm mat depth) was stabilized at around 70-90%, whereas in the superficial (more than 1/2 of the depth) the water saturation degree showed large variations between 30% and 80%. These variations in the shallow layer may contribute to the supply of air for the plant roots. Excessive drainage caused a decrease and considerable imbalance in the water saturation degree in the mat. And the former saturation level could not be restores by standard drip irrigation. It was seemed important during plant cultivation that a level of 50% or more of water saturation was maintained all over the mat. Since rockwool fiber did not effect significantly the content of PO₄³-and Ca²⁺ of the nutrient solution in the mat, such factors can be disregarded in the regulation of the nutrient solution for soilless culture.

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In order to develop an irrigation method for rockwool culture, the flow of the solution and movement of the solvent in the rockwool mat caused by drip irrigation were examined. It was important to set the dripping sites at one side on the surface of the 30 cm width mat, and open the drainage slit near the opposite side of the mat bottom. Then the solution flowed evenly in the mat from the dripping sites to the drainage slit, and the nutrient composition in the mat was uniform. When the dripping sites were moved to the center of the mat surface, only a small amount of the dripped solution flowed to the opposite side of the drainage slit. Consequently, the nutrient composition in the mat was not uniform. When the drainage slits were opened in both sides, or the width of the mat decreased to 20 cm, the composition of the nutrients remained uniform. When half of the mat volume was adequately irrigated, 50% of the solvent drained from the mat, regardless of the water content of the mat and the irrigation intensity. When the irrigation intensity exceeded the plant water uptake, the application of continuous irrigation resulted in a difference in the nutrient composition in the mat depending on the distance from the dripping site. At that time the difference in the nutrient composition between the dripping solution and the drainage one was maximum in the mat. Under such conditions of irrigation, it may be possible to estimate the nutrient composition in the mat by analyzing the composition of the drainage solution.

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Fuzzy logic is able to make use of human behaviour and experience. In this paper, fuzzy control is applied to the adjustment of pH of the solution in deep hydroponic system, resulting its utilization for hydroponic automation, where pH of the solution is controlled by injecting the acid in the storage tank.
Applying the fuzzy logic to the pH-control, the same control pattern of acid injection as a skilled human operator's technique is obtained. Furthermore the controlled characteristics is superior to that of traditional control in its stability.

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