ADVANTAGEOUS ARRANGEMENT OF PLANTS IN A PLANT FACTORY — CULTIVATION OF LETTUCE SUSPENDED UPSIDE DOWN
As a result, there was no significant difference between the growth rates of both lower and upper plants and dry matter of their tops were 14 times as heavy as that before 15 days under the photoperiod of 24 hours and PPFD of 300 μE/m2/s. Although the stem of the upper plant was slightly longer than that of the lower plant, there was no remarkable difference morphologically between both plants. When the PPFD level decreased to 130 μE/m2/s, fresh weight of the top of the upper plant decreased by 25 % and the stem length increased by 98 % compared with the lower plant. On the other hand, when the photoperiod decreased to 12 hours under PPFD of 270 μE/m2/s, dry weight of tops of both plants were similar although the stem of the upper plant was twice as long as the lower plant. In conclusion, this method is valid for making cultivation area per lamp double compared with other conventional methods when the PPFD level is about 300 μE/m2/s.