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in the closed system with no retarded growth compared with the greenhouse. Development of the first flower bud and its growth were enhanced by optimal control of temperature, PPF and photoperiod in the closed system, which would result in earlier harvest of tomato fruits in the greenhouse (Ohyama et al., 2003).

128 cells/tray 200 cells/tray 288 cells/tray cv. House Momotaro

Figure 4. Tomato seedlings grown in the closed system in 128-, 200- and 288-cell trays. There are no significant differences in growth among the treatments. The standard number of cells is 128 or 72 per tray when using the greenhouse for transplant production. Thus, the transplanting density per tray can be at least 1.5 (=200/128) to 2.2 (=288/128) times higher in the closed system than in the greenhouse.

128 cells/tray 200 cells/tray 288 cells/tray cv. House Momotaro

Figure 4. Tomato seedlings grown in the closed system in 128-, 200- and 288-cell trays. There are no significant differences in growth among the treatments. The standard number of cells is 128 or 72 per tray when using the greenhouse for transplant production. Thus, the transplanting density per tray can be at least 1.5 (=200/128) to 2.2 (=288/128) times higher in the closed system than in the greenhouse.

5.1.2. Spinach (Spinacia oleracea)

Spinach transplants were more vigorous when grown for 14 days after sowing on 288-cell trays in the closed system than when grown on 144-cell trays in the greenhouse (Figure 6). Namely, planting density can be doubled in the closed system compared with that in the greenhouse. Bolting of spinach could be inhibited during transplant production by short photoperiod treatment in the closed system, which resulted in delayed bolting when they were subsequently grown under long photoperiod in the greenhouse (Chun et al., 2000). It is essential that bolting in spinach plants at the time of harvest is delayed in order to keep their economic value high.

A single node cutting each with one unfolded leaf of sweetpotato could be grown to a transplant within 14 days. In the greenhouse, it takes at least 20 days, and normally 25 days (Figure 8, Lok et al., 2002). In the closed system, virus-free transplants can be produced easily, which increases the economic values of vegetatively propagated transplants, such as sweetpotato transplants.

Figure 5. Tomato seedlings grown in the closed system 20 days after sowing (DAS). The growth is uniform over the tray.

Greenhouse Closed system

144 cells/tray 288 cells/tray

13 DAS 12 DAS

Figure 6. Spinach transplants grown for 12 days using the 288-cell trays in the closed system are greater, greener and more vigorous than those grown for 13 or 17 days using 144-cell trays in the greenhouse.

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