Quality, Yield, and Biomass Efficacy of Several Hydroponic Lettuce (Lactuca sativa L.) Cultivars in Response to High Pressure Sodium Lights or Light Emitting Diodes for Greenhouse Supplemental Lighting

Abstract

Lettuce is an economically important crop that can be grown either in the field or greenhouse. Different challenges are present in either environment; therefore, cultivar selection is important. For hydroponic greenhouse lettuce there is relatively little published information on cultivar selection under different lighting sources. The objective of phase 1 was to determine the influence of lighting using high pressure sodium (HPS) or light emitting diodes (LED) on plant fresh weight, height, tip burn index, bolting, and Brix. Phase 2 was similar to phase 1 but with fewer cultivars (1) to allow for greater number of replicates per treatment per crop cycle. Each experiment consisted of three crop cycles over time per phase. Light sources were controlled using an algorithm, Light and Shade System Implementation (LASSI), to achieve a constant average daily light integral under each treatment and crop cycle. Electrical consumption and efficacy (fresh weight per kWh) from each treatment was estimated using data collected on power consumption from representative lamps multiplied by the number of fixtures and the hours fixtures were on per crop cycle. In phase 1, the fresh weight of 2 to 3 cultivars was greater under HPS and 1 to 2 cultivars under LED, depending on production cycle. The HPS-grown lettuce tended to have more tip burn and bolting in crop cycles 1 and 2, with cycle 3 showing similar tip burn incidence. Bolting was only consistently observed in one cultivar, ‘Teodore’. The LED array used less than half as much electricity as the HPS array, while producing relatively similar size lettuce, therefore, leading to electrical efficacies two- to three-times higher in LED than in HPS treatments. In phase 2, significant differences in height were found in ‘Greenstar’ and ‘Xandra’, with HPS producing larger plants than LED. Significant differences were also found in diameter in ‘Greenstar’, ‘Xandra’, ‘Locarno’, and ‘Crunchita’, with HPS again being larger than LED.

Increased Plant Quality, Greenhouse Productivity and Energy Efficiency with Broad-Spectrum LED Systems: A Case Study for Thyme (Thymus vulgaris L.)

“…Our power consumption results and thus the potential of LEDs for reducing energy costs coincide with numerous studies and reviews [ 6 , 9 , 59 ], stating energy reductions up to 70% compared to traditional light sources while producing similar crop yields at equal light intensities, and confirm the current trend of LEDs’ increasing photon efficiencies: While HPS and LED fixtures had nearly identical photon efficiencies until ~2015 [ 6 , 35 ], the best evaluated LED fixture was 40% more photon-efficient than HPS due to technological improvements of LEDs within the PAR region soon after [ 35 , 59 ]. A current study by Hernandez et al (2020) confirms the corresponding increase in biomass efficacy of LEDs, as their LED treatment led to a 2.4 to 3.1 times greater biomass efficacy than HPS, which matches our findings [ 60 ]. Another study in which LED and FL treatments were compared, reported a biomass efficacy three to five times higher under LED than under FL lighting [ 61 ].…”

Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids

“…Decreasing the blue fraction from 20% to 4% resulted in a 12.3% increase in dry mass yield, while increasing the efficacy from 1.72 to 2.51 μmol J -1 resulted in a 27% increase in yield per dollar of electricity. Similar results were reported for 13 lettuce cultivars grown in greenhouses supplemented with HPS or LED lights [23].…”

“…Snowden et al [19] saw little to no effect on morphology in multiple species when increasing the fraction of green from 2 to 41% at about 11% blue. By contrast, multiple studies (including the studies that found no effect of substituting green and red photons) have shown a reduction in leaf area and dry mass gain with an increasing blue photon fraction from 5 to 30% [17][18][19][20][21][22][23][24][25].…”

“…Although growth parameters (e.g. height, fresh weight) vary among cultivars within a species, the effects of spectra on these parameters are expected to be small [23]. About 7% of the 12% reduction in yield can be accounted for by lower YPF, a response that is consistent across species [9].…”

Challenges and Opportunities of Light-Emitting Diode (LED) as Key to Modulate Antioxidant Compounds in Plants. A Review

“…Overall, understanding the physiological responses induced by LED lights is a crucial step to regulate plant morphogenesis, enhance the nutritive value of crops, and preserve quality in postharvest fresh products. However, data from the literature are often contradictory because, over the years, many research projects focused their efforts on a few selected species or cultivars, and little is known about the comparison among closed species, more cultivars, or types of the same cultivar [ 22 , 169 , 200 , 201 ]. Eventually, further efforts should be devoted to including harmonized LED metrics and to comparing different light qualities and intensities in the same experimental design.…”