The aim of this study was to determine the optimum photoperiod of supplemental lighting to obtain high fruit yields in forcing culture of strawberry. Strawberry plants were illuminated with supplemental lighting provided by high-irradiance light-emitting diodes with photoperiods of 24, 16, 14, or 12-h daily under the controlled air temperature conditions set the ventilation starting temperature at 26°C and minimum air temperature at 6°C from October to May. Compared with plants in the other treatments and the control, those in the 12-h photoperiod treatment showed a significant increase in leaf photosynthesis and earlier differentiation of flower buds on the second inflorescence. These physiological changes resulted in the large amounts of carbon translocation from leaf to fruit, leading to the fruit quality improvement and the highest marketable yield among all of the treatments. When the photoperiod of supplemental lighting exceeded 12 h per day, flower opening on the first inflorescence was accelerated, but flower bud initiation on the second inflorescence was inhibited. This inhibition caused a decrease in leaf photosynthesis, leading to excessive carbohydrate accumulation in the leaves, resulting in lower total fruit yield than that from plants in the 12-h photoperiod treatment. These data show that a 12-h photoperiod of supplemental lighting is appropriate to obtain high yields in forcing culture of strawberry.

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As a problem associated with the cultivation of lettuce, the growth of stem and floral stage are facilitated under a high temperature, which will eventually reduce its quality. To address this problem, cultivation under low-temperature conditions is considered. However, it is difficult to cultivate lettuce while controlling the temperature because of the production cost, and growth control technologies based on photo-morphogenesis are attracting attention. An experiment was conducted on the growth control of lettuce under a high-temperature involving End-of-day light irradiation using LED light source. The seeds of lettuce were sown on January 16 and August 23, 2012, and the plants were placed under a high temperature (30°C) and exposed to the light on January 22 and August 28, 2012. Far-red and red LED lights were used as light sources. No light source for irradiation treatment was placed in the third treatment, as the control. Sixty days after the treatment of Manoa by the far-red light treatment, the stem length was the longest, and the floral stage was the highest. The results of the experiment on lettuce cultivation under a high-temperature suggest that End-of-day light irradiation using LED light source effectively controls the growth of lettuce.

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The quality of groundwater is essential to ensuring the sustainable use of water resources for irrigation. Deep groundwater samples were collected from the Sambagawa Belt in southeastern Japan, at 1,180 m (GW_deep) and 50 m (GW_shallow). Groundwater quality was assessed based on analysis of physicochemical parameters. The sodium adsorption ratio of groundwater fell in the range of 1.61–3.13, while electric conductivity of GW_deep was high (›75.0 mS m⁻¹). Experiments were performed to determine the effects of deep groundwater on germination and early growth of komatsuna (Brassica rapa var. perviridis). Strong inhibition (44% reduction) of root growth was observed with GW_deep compared to the control treatment. In contrast, shoot length increased with increasing depth of the groundwater source. Comparison of the effects of GW_deep and NaCl solution on growth of komatsuna revealed similar patterns at 1×10³ mg L⁻¹ NaCl solution. Our findings suggested that deep groundwater can be used for irrigation of komatsuna, but not during the germination stage of this crop.

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In this study, a speaking plant-based optimal control system was proposed and applied to promote the initial growth of tomatoes in hydroponics. The control system consisted of a feedback control system and a decision system. The decision system consisting of neural networks and genetic algorithms was used to determine the optimal l-step set point of nutrient concentration which maximizes the initial growth of tomatoes. In the decision system, the growth rate of plant height to nutrient concentration was first identified using neural networks and then the optimal 6-step set points were determined through simulating the identified model using genetic algorithms. One step is 7 days. The optimal value (6-step set points) was 1.0 for the 1st step, 0.5 for the 2nd step, 0.8 for the 3rd step, 0.9 for the 4th step, 1.1 for the 5th step, and 1.2 dS m⁻¹ for the 6th step during the initial growth stage. There was a significant reduction (0.5 dS m⁻¹) in nutrient concentration in the second step and this significant reduction corresponds to nutrient stress. Actual plant growth for optimal control was about 1.15 times larger than that for conventional control. We suggest that this control technique is suitable for optimizing hydroponic cultivation processes and the control strategy, including nutrient stress application, is effective in promoting plant growth.

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In this study, changes in the levels of ascorbic acid and dehydroascorbic acid (vitamin C content) in lettuce and spinach by potassium restriction from the middle of the cultivation stage using a water culture medium were examined. It was presumed that the content of glucose, which occurs as an ascorbate matrix, increased in a plant by osmoregulation using potassium restrictions treatment, resulting in an increase in vitamin C content. Vitamin C content in green lettuce, frilly lettuce, and spinach after potassium restriction were 1.9, 1.5, and 1.4 times higher than that in the control, respectively, whereas that in red leaf lettuce did not change. Glucose content in red leaf lettuce, frilly lettuce, and spinach after potassium restriction was 4.0, 1.7, and 2.4 times higher than that in the control, respectively. The activity of L-galactono-γ-lactone dehydrogenase (GLDH), which catalyzes ascorbic acid synthesis, after potassium restriction in frilly lettuce and spinach was 2.2 and 1.8 times higher than that in the control, respectively, whereas that in red leaf lettuce and green lettuce did not change. These results indicate that vitamin C content increased by restricting the levels of potassium in a water culture medium from the middle of the cultivation stage, although responses varied among cultivars.

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Fogging and circulation systems were installed into a greenhouse to control daytime humidity and airflow at adequately high levels, with systems composed of 9 mist sprayers and 2 fans with a diameter of 0.3 m. The performance of the systems was examined by analyzing humidity (vapor pressure, relative humidity), wind speed, and leaf conductance (total conductance of stomata and leaf boundary layer) of cucumber plants under 2 conditions: with mist and fan treatment and with no treatment. Use of the systems brought increases in relative humidity from 22% to 76% and wind speed from 0.16 to 1.08 m s⁻¹ at the center of the greenhouse, and further increased effects were also found over the cultivation area. Moreover, such increases in humidity and wind speed accelerated the leaf conductance by approximately 1.5 times. The results suggest that fogging and circulation systems could improve the greenhouse environment and leaf gas exchange during daytime.

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This study was intended to verify the effects of H₂-enriched electrolyzed water in hydroponic nutrient solutions, as well as its mechanism. In the experiment, a “Reduced Vegetable Water Purifier” H₂-enriched electrolyzed water producing system, which was supplied by Nihon Trim Co., Ltd., was used. According to the measurements in which ORP electrodes were used as an indicator of oxidation-reduction power, the H₂-enriched electrolyzed water showed superior reduction power, reaching levels as low as −113 mV. The germination and early growth tests performed on the Komatsuna plants revealed that the roots grew significantly longer in the H₂-enriched electrolyzed water than in the control. Komatsuna plants were cultivated by the NFT methods in a nutrient solution prepared using H₂-enriched electrolyzed water. This study demonstrates that the nutrient solution in which H₂-enriched electrolyzed water was used promoted the growth of leaves and roots of Komatsuna plants.

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The greenhouse heating method widely used in Japan, involves the circulation of warm water or warm air by burning heavy oil. However, in recent years the cost of fuel has been rising, and an alternative fuel to heavy oil has been sought by consumers. We propose a new greenhouse heating method using a clean GTL fuel. GTL (Gas to Liquids) fuel is made from natural gas, and contains no sulfur and no aromatics as a source of the odor of petroleum. Therefore, the exhaust gas contains only water vapor and carbon dioxide, without the occurrence of odor, sulfur oxides or soot. In the case of heavy oil combustion, due to the toxic components contained in the exhaust gas, it has to be discharged outside of the greenhouse. Depending on the old or new combustion models, the exhaust heat loss becomes as large as 15–30% of the combustion energy. The GTL combustion method by confining the greenhouse exhaust gas, no heat loss to the outside. Further, it is possible to obtain the effect of carbon dioxide enrichment to plants, and this method contributes to the reduction of carbon dioxide emissions.

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