Response of hydroponic baby leaf greens to LED and HPS supplemental lighting

Authors: MATTSON, NEIL - Cornell University; ALLRED, J - Cornell University; DE VILLIERS, D - Cornell University; SHELFORD, TIMOTHY - Cornell University; Harbick, Kale

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2022
Publication Date: 3/8/2022
Citation: Mattson, N.S., Allred, J.S., De Villiers, D., Shelford, T., Harbick, K.J. 2022. Response of hydroponic baby leaf greens to LED and HPS supplemental lighting. Acta Horticulturae. 1337:395-402. https://doi.org/10.17660/ActaHortic.2022.1337.54.
DOI: https://doi.org/10.17660/ActaHortic.2022.1337.54

Interpretive Summary: Lettuce, arugula and kale were grown in a greenhouse under high-pressure sodium (HPS) or light emitting diode (LED) supplemental lighting. The plants were grown with daily light integral (DLI) control so they received the same amount of light each day. The most significant finding is that seasonal variation was seen in which light source performed best in terms of fresh weight, dry weight, and total yield. In winter, lettuce grown under HPS performed better, while in fall, lettuce grown under LED performed better. We hypothesized that the difference was due to leaf temperature differences which were higher under HPS due to the presence of more infrared radiation, and this would be a benefit in winter but potentially a detriment in other seasons. This suggests that plants are not as sensitive to the spectrum of greenhouse supplemental light sources with the presence of natural light in the background, compared to sole-source environments like plant factories (indoor farms).

Technical Abstract: The project objective was to determine the response of baby leaf greens to greenhouse supplemental lighting source. In the first experiment, plants were grown under five LED sources and two HPS sources for three crop cycles. In the second experiment, sequential crops were grown in a greenhouse for one year under one HPS and LED fixture type selected from experiment 1 based on crop biomass and energy efficacy (Philips GreenPower LED Toplighting Deep Red/Blue – Low Blue and HPS Gavita Pro 6/750e FLEX DE). In both experiments seeds of arugula (Eruca sativa ‘Astro’), kale (Brassica napus subsp. napus var. pabularia ‘Red Russian’), lettuce (Lactuca sativa ‘Outredgeous’) were sown at 1550 seeds m-2 density into a peat-based substrate in Speedling rafts. Rafts were placed in a germination chamber for 2 days and then floated on hydroponic ponds with a modified Sonneveld’s nutrient solution in a greenhouse where they received lighting treatments for 11-14 days. Light quantum sensors under each treatment were connected to a light and shade control algorithm to achieve a daily light integral (DLI) of 17 mol m-2 d-1. In experiment 1 only subtle differences were found in plant biomass and morphology in response to seven lighting treatments. The fresh mass (FM) of arugula, kale, and lettuce averaged 2.7, 1.9, and 3.0 g plant-1 across lighting treatments. For arugula FM, one LED source performed significantly better than two other LED sources. For kale FM, no significant differences were found based on treatment. For lettuce FM, two HPS sources and one LED source performed better than one LED source. In experiment 2, while DLI was controlled, some seasonal patterns were found. Overall, FM, dry mass (DM), and total yield was greater in the fall and lower in the winter and early spring. In winter there was a slight increase in FM/DM under HPS. In fall there was a slight FM/DM benefit to LED. Averaged over the calendar year, arugula and lettuce did not exhibit differences in FM/yield based on light source, while kale had a slight increase in FM/yield under HPS. The monthly differences in biomass based on light source may be due to light effects on plant temperature.