Response of greenhouse tomato to different vertical spectra of LED lighting under overhead high pressure sodium and plasma lighting
Hao, X.M., Guo, X.-B., Zheng, J.M., Little, C., Khosla, S., and Chen, X. (2016 In press). Response of greenhouse tomato to different vertical spectra of LED lighting under overhead high pressure sodium and plasma lighting, Acta Hortic (ISHS). (in press).
Different light spectra trigger different plant processes. Therefore, the optimum light spectrum for various plant growth processes such as leaf and fruit growth may be different. In tall greenhouse crops such as tomatoes, most of the leaf/vegetative growth occurs in the top and middle canopy while fruit growth occurs in the middle and bottom canopy. Therefore, optimized vertical light spectral distribution profiles could be developed for improving both vegetative and fruit growth. In this study, we investigated the effect of different vertical spectra of light emitting diodes (LED) lighting under high pressure sodium (HPS) and plasma overhead lighting on plant growth, fruit yield and quality of tomato (Solanum lycopersicum). The study was conducted from October, 2013 to April, 2014 in a large greenhouse divided into 4 sections (50 m2 growing area in each section). Two sections were installed with plasma overhead light while the other two sections with HPS light, with both of them provided the same amount of overhead light (165 μmol m-2 s-1). Four vertical LED regimes (the top far-red with bottom blue; the top blue with bottom far-red; the top far-red with bottom red; the top red with bottom far-red) were applied to the 4 plots inside each of the 4 sections. The top LEDs were placed just above the crop canopy while the bottom LEDs were placed at 20 cm above the cluster of fruit reaching its full size. The red and blue LEDs provided 10 µmol m-2 s-1 while far-red LED provided 8 µmol m-2 s-1 of light. The plasma and HPS overhead lights had similar total cumulative yield over the 5 months of fruit harvest. The top far-red with bottom blue LED achieved the best fruit yield and quality under plasma light while the top far-red with bottom red LED had the best performance under HPS. Furthermore, the effects of the LED lighting were affected by their positions in the crop canopy; far-red LED light should be placed just above the crop canopy instead of in the bottom canopy. This study has demonstrated that optimized vertical light distribution profiles can be developed for improving both plant growth, and fruit yield and quality in year-round greenhouse tomato production with supplemental lighting.
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