Hybrid Lighting Configurations with Top HPS Lighting and LED Inter-lighting and N:K ratios in Nutrient Feedings Affected Plant Growth, Fruit Yield, and Light and Energy Use Efficiency in Greenhouse Tomato Production

Year-round greenhouse vegetable production with artificial lighting in northern regions is capital and energy intensive. To be successful, the lighting system and crop/nutrient management must be optimized to maximize crop productivity and light and energy use efficiency (LUE and EUE). Light emitting diodes (LEDs) is energy-efficient, and can be used as inter-lighting inside crop canopy (because of its low surface temperature) to improve canopy vertical light distribution and LUE and EUE. However, it is much more expensive than HPS (high pressure sodium lamps, high operation temperature). Therefore, it will be more economical feasible to use a hybrid lighting system using HPS as top light and LED as inter-lighting. In this study, two greenhouse trials were conducted from Fall 2012 to Spring 2013 to evaluate various lighting configurations with top HPS lighting and LED inter-lighting and nutrient treatments (N:K ratio) to develop and optimize the hybrid lighting system and nutrient supply for greenhouse tomato production with lighting. Trial one evaluated nine lighting configurations [3 top light levels (0, 120, or 200 µmol·m^-2·s^-1 of HPS) × 3 inter-light levels (0, 37, or 74 µmol·m^-2·s^-1 of LED inter-lighting)] on a vigorous beefsteak tomato cultivar DRW7749. Trial two tested various 3 levels of top HPS lighting and LED inter-lighting on a generative cluster tomato cultivar Komeet. Three nutrient (N:K ratio, 1:1, 1:2, and 1:3 ppm:ppm) treatments were applied within each lighting configuration in both trials. The best lighting configuration for 'DRW7749' seemed to be 120 µmol·m^-2·s^-1 top HPS lighting plus 74 µmol·m^-2·s^-1 of LED inter-lighting (a top to inter-lighting ratio of 3:2), which had the highest LUE and EUE. The lighting configurations with various ratios of top HPS and LED inter-lighting had similar LUE and EUE in the early stage of fruit production. However, the LUE and EUE of the lighting configurations with higher proportion of LED inter-lighting was higher than those with low proportion of LED inter-lighting in late stage of fruit production, indicating LED allowed the plant to maintain its vigour until late stage of fruit production. This was especially true for the generative cultivar Komeet. The highest fruit yield was achieved with a N:K ratio of 1:2 in the nutrient feeding for cultivar DRW7749 while it was achieved with N:K ratio of 1:1 for 'Komeet', especially in late production period, indicating the generative cultivar required higher nitrogen supply to maintain vegetative growth/plant vigour when grown with lighting.