Abstract
Lettuce plants (Lactuca sativa L.) were grown under 2 levels of intensity in combination with 3 levels of irradiating hour. Plants grown under higher photosynthetic photon flux densities (PPFD) and longer photoperiod increased fresh and dry weights. However, inferior quality with the increased axillary buds and the curling of heart leaves were found in the plants under high PPFD with a photoperiod of 12 h. There was no significant difference between the plants grown under same integral amounts of PPFD × photoperiod. The present experiment indicates that an optimum PPFD of 400-420 umol⋅s-1⋅m-2 with 8 h photoperiod increases lettuce growth and crop quality. It is may be suggested that high light intensity with short day regimes (11.00 pm-7.00 am) will be commercially recommended for lettuce production in the artificially controlled plant factory.
