Comparison of supplemental lighting from high-pressure sodium lamps or light-emitting diodes on morphology and nutrient uptake of greenhouse crops

Authors: Boldt, Jennifer; Altland, James

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2021
Publication Date: 4/13/2022
Citation: Boldt, J.K., Altland, J.E. 2022. Comparison of supplemental lighting from high-pressure sodium lamps or light-emitting diodes on morphology and nutrient uptake of greenhouse crops. Acta Horticulturae. 1337:313-322. https://doi.org/10.17660/actahortic.2022.1337.42.
DOI: https://doi.org/10.17660/actahortic.2022.1337.42

Interpretive Summary: Supplemental lighting provided to greenhouse crops during winter and spring production augments ambient sunlight to provide sufficient light for desired crop growth, development, and morphology. High-pressure sodium (HPS) lamps are the predominant supplemental light source in greenhouses. Light-emitting diodes (LEDs) are a potential alternative but high capital costs and a lengthy return on investment have impeded their adoption. Limited research has been done to compare HPS lamps and LED fixtures for supplemental greenhouse lighting, and growers have concerns about the spectral effects on growth, morphology, and nutrient uptake of container-grown ornamentals and vegetables. Our objective was to compare growth and morphology of eight greenhouse crops provided supplemental light from HPS lamps or LEDs (red, blue, and far-red). Plants grown with supplemental LED lighting were generally taller and wider, with greater dry mass compared to plants grown with supplemental HPS lighting. Foliar nutrient concentrations varied with crop and supplemental light source. However, all crops were of acceptable quality regardless of HPS or LED supplementation. Therefore, selection of light fixtures for supplemental lighting in the greenhouse can be chosen based on desired crop characteristics and associated capital and operating costs.

Technical Abstract: Supplemental lighting in greenhouses augments ambient sunlight, especially during winter and spring production to provide sufficient irradiance for desired growth. Light-emitting diodes (LEDs) are increasingly used in place of high-pressure sodium (HPS) lamps, but growers are hesitant to switch due to price and concerns about spectral effects on growth, morphology, and nutrient uptake. Eight greenhouse crops [basil (Ocimum basilicum ‘Genovese Emily’), geranium (Pelargonium ×hortorum ‘Maverick Red’), pansy (Viola ×wittrockiana ‘Delta Premium Blue Blotch’), pepper (Capsicum annuum ‘California Wonder’), spinach (Spinacia oleracea ‘Whale’), tomato (Solanum lycopersicum ‘Early Girl’), vinca (Catharanthus roseus ‘Cora Burgundy), and zinnia (Zinnia marylandica ‘Zahara Cherry’)] were grown in a glass greenhouse and provided a supplemental photosynthetic photon flux density of 100 µmol'm-2's-1 14 h per day from HPS or LED (50 blue: 50 red: 22 far-red) fixtures. Plants receiving supplemental LED lighting were 11% to 99% taller, 4% to 45% wider, and had 25% to 143% greater dry mass than plants receiving supplemental HPS lighting. Relative chlorophyll content was 102% higher in LED-supplemented basil, but 5% to 26% lower in the other seven species, compared to HPS-supplemented plants. Foliar nutrient concentrations of LED-supplemented plants were 2% higher to 14% lower (nitrogen), 10% higher to 20% lower (phosphorus), 3% to 32% lower (potassium), 15% higher to 9% lower (calcium), 28% higher to 12% lower (magnesium), 11% higher to 18% lower (sulfur), 30% higher to 18% lower (boron), 23% higher to 34% lower (copper), 2% to 40% lower (iron), 13% to 41% lower (manganese), and 14% higher to 31% lower (zinc), relative to HPS-supplemented plants.