Twofold Increase in Strawberry Productivity by Integration of Environmental Control and Movable Beds in a Large-scale Greenhouse

In Japanese strawberry production, over 90% of farmers employ forcing culture in which fruits are harvested from winter to the following spring using June-bearing cultivars. However, production areas are continuously declining for Japanese strawberry production. The average yield from domestic strawberry production in 2012 was about 3 kg m 2 (t / 10a). The average yields in the main production districts of Tochigi and Fukuoka in 2012 was about 4 kg m 2 according to statistical data from the Ministry of Agriculture, Forestry and Fisheries in Japan. To reverse the decline in Japanese strawberry production, there is an increasing trend for strawberry production in large-scale industrial facilities. Techniques to obtain consistently high yields are required in large-scale greenhouse production. In strawberry production, many factors contribute to fruit yield (Hidaka et al., 2014a). Fruit yield per unit land area is determined by the number of plants and the fruit yield per individual plant. The former is influenced by cultivation systems, and the average planting density of the conventional bench culture system with stationary beds is about 8 plants m 2 (8,000 plants / 10 a) in Japan. To achieve high planting density, many types of the movable bed systems, e.g., the lateral movable type (Nagasaki et al., 2013), the circulative movable type (Hayashi et al., 2011) and the vertically movable type (Hidaka et al., 2012), have been developed. These lateral, circulative and vertically movable bed systems enable efficient use of the greenhouse space, and result in 1.5, 2.5 and 4 times planting densities as compared with the conventional bench culture system, respectively. The fruit yield per individual plant is influenced by many factors, such as unit fruit weight, fruit number per plant, flower bud, photosynthate partitioning, leaf photosynthesis, and water and nutrient uptake by roots. These factors are affected by the environment (e.g., light intensity, photoperiod, temperature, CO2 concentration, humidity, and wind velocity) and the genetic potential of each cultivar. In our previous studies, we explored the development of a supplementary lighting technique, i.e., selection of an effective light source (Hidaka et al., 2013) and determination of the optimum photoperiod for supplemental lighting (Hidaka et al., 2014b). Furthermore, we compared the effect of supplemental lighting among cultivars and observed a remarkable increase in yield in the June-bearing cultivar ‘Benihoppe’ (Hidaka et al., 2015). To achieve an even higher increase in fruit yield, a combinational approach to environmental control, considering not only the light environment but also CO2 concentration and air temperature, for example, is required. Kawashima (1991) reported the effect of CO2 en-