Effects of supplemental lighting from 23:00 to 7:00 on growth of vegetables cultured by NFT

Abstract

Effects of supplemental lighting 23:00-7:00 on the growth and photosynthesis of vegetable crops were studied. In Experiment 1, lettuce (Lactuca sativa L.), pakchoi (Brassica campestris L. var. chinensis) and tsukena (Brassica campestris L.) grown on NFT in a greenhouse, were subjected to supplemental lighting with high pressure sodium lamps. Plants were grown for 24 days under normal photoperiod and then separated into 5 groups, as follows; subjected to supplemental lighting 1) for 24 days, 2) first 8 days, 3) the second 8 days, 4) the last 8days of the 24 days period and control continued natural photoperiod. In Experiment 2, lettuce, garland chrysanthemum (Chrysanthemum coronarium L.) and tomato (Lycopersicon esculentum Mill.) plants were grown under the light source and 1, 2, and 3m apart horizontally away from the light source. Results obtained are as follows; 1. In Experiment 1, supplemental lighting for 24 days increased top fresh weights of all crops. In lettuce and pakchoi, the supplemental lighting for the second 8 or last 8 days increased the top fresh weights when compared to the control. 2. In lettuce, garland chrysanthemum, and tomato, growth increased with increasing light intensity of the supplemental lighting; in garland chrysanthemum it enhanced the dry weights of stems. 3. Supplemental lighting increased the chlorophyll concentrations as measured with a Minolta chlorophyll meter, SPAD-502; the increment levels corresponded to the light intensity of the supplemental lighting. The increases in SPAD values under supplemental lighting appeared on the 8th day after the onset of the supplemental lighting. However the elevated SPAD values resulting from supplemental lighting decreased to the same levels as the control during the subsequent 8 days when supplemental lighting was halted. 4. Supplemental lighting during the night accelerated the photosynthetic rates of lettuce, garland chrysanthemum, and tomato plants, in addition, plants grown under supplemental lighting maintained a higher photosynthetic rates during the day than the control plants did.