Introduction

A 'closed plant production system' or simply a 'closed system' has been commercialized in Japan since 2002, largely based upon the research at Chiba University, for production of tomato, cucumber, eggplant, lettuce and spinach transplants from seeds. Commercial productions of herbs, leafy vegetables, bedding plants such as pansy, medicinal plants, and orchid plants are now under trial in Japan.

The closed system is defined as a warehouse-like structure covered with opaque thermal insulators, in which ventilation is kept at a minimum, and lamps are used as the sole light source for plant growth.

Advantages of the closed system over a greenhouse for producing high quality transplants include: 1) rapid and efficient growth of transplants mainly resulting from a considerably higher light utilization efficiency (2-3 times) of transplants due to optimized growth conditions, 2) the significantly higher quality transplants produced under uniformly controlled environments in the protected area free from pest, insects/pathogens and the disturbance of outside weather, 3) the higher (about 10 times) productivity per floor area per year, mainly due to the use of multi-layered shelves (e.g., 4-5 shelves) with the ratio of planting area to floor area of 1.2-1.5, a high planting density per tray area (1,500 transplants m-2), a high percentage of salable transplants (>90%), higher sales price due to their higher quality and uniformity of transplants (10-20% over greenhouse), and shorter production period (30-70% of greenhouse), 4) the drastically higher utilization efficiencies of water, CO2, (about 15 times for water and 2 times for CO2) and fertilizers mainly due to the minimized ventilation and recycling use of dehumidified water by air conditioners, resulting in little waste water to the outside, 5) virtually no requirement of heating cost even in the winter because of its thermally insulated structure 6) the lower labor cost (50% or less) due to the smaller floor area, the worker-friendly shelves, comfortable working environments), and 7) the easier control of plant developments such as stem elongation, flower bud initiation, bolting, root formation (Kozai et al., 1998; Kozai, 1998; Kozai et al., 1999; Kozai et al., 2000a, b and c; Chun and Kozai, 2001, Kozai et al., 2004).

High electricity cost and initial investment are often mentioned as a disadvantage of the closed system. However, electricity cost for transplant production could be reduced considerably by using thermally insulated walls and multi-shelves, and advanced lighting and air conditioning systems (Kozai, et al., 2004). The electricity cost for lighting and cooling per transplant was found to be roughly 0.5 to 1.0 US cent, which accounts for 1-5% of the sales prices of tomato, eggplant, pansy, and sweetpotato transplants in Japan.

Since only about 10% of greenhouse floor area is required to produce the same amount of transplants, initial cost per annual plant production in closed systems is lower than that in greenhouses. By using a closed system with a floor area of 150 m2 with 60 shelves having 960 plug trays in total, about 10 million transplants can be produced annually.

In this chapter, the definition, concept, theoretical backgrounds, methods, materials, applications, and advantages of the closed system using lamps over a greenhouse using sunlight are described from biological, engineering and economic points of view.

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