2017 ASHS Annual Conference

Different spectra of light triggers different plant growth processes. Therefore, the optimum light spectrum or spectral compositions for various plant growth processes such as leaf and fruit growth may be different. Greenhouse fruiting vegetables, such as tomatoes and sweet peppers, are of tall crop, with most of leaf growth occurred in the top and middle canopy while fruit growth in the middle and bottom canopy. Therefore, not only light spectral composition but also vertical distribution should be optimized/developed to improve both vegetative and generative growth, and fruit quality. The availability of light emitting diodes (LEDs, narrow spectral band and low surface temperature for intra-canopy application) has made it possible. Therefore, a research project was initiated in 2015 to optimize light composition and vertical distribution for greenhouse fruiting vegetables grown with supplemental lighting. The experiments were conducted from Oct. to Mar. in a large greenhouse (200m²). The greenhouse was divided into 4 sections (50m²/section) so that 2 different overhead (above crop canopy) light spectral compositions can be applied with 2 replications. Four different intra-canopy light spectral compositions were applied to 4 plots inside each section. Therefore, a total of 8 vertical light spectral composition and distribution regimes were tested in the experiments. Same amount of overhead light and intra-canopy light was applied in all 8 regimes. The light composition and distribution regimes resulted in significant difference in leaf photosynthesis and plant growth in tomatoes and sweet peppers. This study has clearly demonstrated that optimized light composition and vertical distribution regimes can be developed for improving both plant growth and fruit yield & quality in greenhouse tomato and sweet pepper production with supplemental lighting.