Intensity of Sole-source Light-emitting Diodes Affects Growth, Yield, and Quality of Brassicaceae Microgreens

Abstract

<jats:p>Indoor farming is an increasingly popular approach for growing leafy vegetables, and under this production system, artificial light provides the sole source (SS) of radiation for photosynthesis and light signaling. With newer horticultural light-emitting diodes (LEDs), growers have the ability to manipulate the lighting environment to achieve specific production goals. However, there is limited research on LED lighting specific to microgreen production, and available research shows that there is variability in how microgreens respond to their lighting environment. The present study examined the effects of SS light intensity (LI) on growth, yield, and quality of kale (<jats:italic>Brassica napus</jats:italic> L. ‘Red Russian’), cabbage (<jats:italic>Brassica oleracea</jats:italic> L.), arugula (<jats:italic>Eruca sativa</jats:italic> L.), and mustard (<jats:italic>Brassica juncea</jats:italic> L. ‘Ruby Streaks’) microgreens grown in a walk-in growth chamber. SS LEDs were used to provide six target photosynthetic photon flux density density (<jats:italic>PPFD</jats:italic>) treatments: 100, 200, 300, 400, 500, and 600 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup> with a photon flux ratio of 15 blue: 85 red and a 16-hour photoperiod. As LI increased from 100 to 600 μmol·m<jats:sup>−2</jats:sup>· s<jats:sup>−1</jats:sup>, fresh weight (FW) increased by 0.59 kg·m<jats:sup>−2</jats:sup> (36%), 0.70 kg·m<jats:sup>−2</jats:sup> (56%), 0.71 kg·m<jats:sup>−2</jats:sup> (76%), and 0.67 kg·m<jats:sup>−2</jats:sup> (82%) for kale, cabbage, arugula, and mustard, respectively. Similarly, dry weight (DW) increased by 47 g·m<jats:sup>−2</jats:sup> (65%), 45 g·m<jats:sup>−2</jats:sup> (69%), 64 g·m<jats:sup>−2</jats:sup> (122%), and 65 g·m<jats:sup>−2</jats:sup> (145%) for kale, cabbage, arugula, and mustard, respectively, as LI increased from 100 to 600 μmol·m<jats:sup>−2</jats:sup>· s<jats:sup>−1</jats:sup>. Increasing LI decreased hypocotyl length and hue angle linearly in all genotypes. Saturation of cabbage and mustard decreased linearly by 18% and 36%, respectively, as LI increased from 100 to 600 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup>. Growers can use the results of this study to optimize SS LI for their production systems, genotypes, and production goals.</jats:p>

Blue versus Red Light Can Promote Elongation Growth Independent of Photoperiod: A Study in Four Brassica Microgreens Species

“…Also, under 16-h lighting, B vs. R light promoted elongation without compromising yield compared with 24-h lighting. Crop yield is important for microgreen growers because it directly affects economic return (Jones-Baumgardt et al, 2019). It implies that if blue light is used for microgreen production, shortening photoperiod from 24 h to 16 h may potentially reduce lighting cost and increase production efficiency.…”

“…Within the same species, data bearing the same letter are not significantly different at P # 0.05, according to Duncan's new multiple range test. color) of microgreens, after 7-d blue light treatment, exposing these plants to red light for some days may be an option because these microgreen species can be harvested without or with unfolded first true leaves (i.e., 7-8 d or 11-14 d after seeding) (Jones-Baumgardt et al, 2019). This needs further study to confirm the feasibility.…”

“…Microgreens are consumed when cotyledons are fully expanded, retaining their typical color, with or without appearance of the first true leaves (Jones-Baumgardt et al, 2019;Kyriacou et al, 2016). Microgreens can be grown in varying scenarios, including outdoor, greenhouse, and indoor environments (Kyriacou et al, 2016).…”

Microgreen nutrition, food safety, and shelf life: A review

“…Using a 16‐hr photoperiod and light /dark temperature of 20/16 °C, they found that 15% blue light was optimal for cabbage, but recommended 5% blue light for kale, arugula, and mustard. Increasing light intensity from 100 to 600 µmol m −2 s −1 , while keeping the blue: red ratio steady at 15:85, resulted in asymptotic increase in fresh weight and dry weight, but approximately a linear decrease in hypocotyl length and hue angle for all four Brassicaceae species (Jones‐Baumgardt, Llewellyn, Ying, & Zheng, ). Leaf area was maximal at different light intensities for different species (Jones‐Baumgardt et al., ).…”

“…Increasing light intensity from 100 to 600 µmol m −2 s −1 , while keeping the blue: red ratio steady at 15:85, resulted in asymptotic increase in fresh weight and dry weight, but approximately a linear decrease in hypocotyl length and hue angle for all four Brassicaceae species (Jones‐Baumgardt, Llewellyn, Ying, & Zheng, ). Leaf area was maximal at different light intensities for different species (Jones‐Baumgardt et al., ). Increasing blue light intensity 3 days prior to harvest at 23 days decreased nitrate content in tatsoi, but reduced ascorbic acid content in plant leaves (Simanavičius & Viršilė, ).…”