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beneficial to both accumulators and nonaccumulators. Its benefits include increased tolerance to biotic and abiotic stress in both field and controlled environment agriculture ( Brown et al. 2022 ; Dey 2022 ; Verma et al. 2021 ). Supplementation of Si has

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extended to Controlled Environment Agriculture Program and EuroFresh Farms for the technical and financial support.

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LED technology is fundamentally altering the use and application of supplemental lighting for controlled environment agriculture. This paper provides a brief overview of the rapid development of LED lighting and some thoughts on the future

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microenvironment. The plants were cultivated in a greenhouse at the Controlled Environment Agricultural Center, University of Arizona ( Table 2 ). Temperature and relative humidity measures for each trial represent means derived from eight individual stations

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The term controlled-environment agriculture (CEA) was first introduced in the 1960s and refers to an intensive approach for controlling plant growth and development by capitalizing on advanced horticultural techniques and innovations in technology

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‘Cherokee Purple’ tomato (Solanum lycopersicum L.) plants are a highly sought-after heirloom cultivar in the United States but are low yielding and highly susceptible to soil-borne pathogens, and may benefit from being grafted. Soilless systems such as aquaponics and hydroponics help increase yield, mitigate disease, and serve as an alternative to field production. The objective of this study was to evaluate a grafting combination of ‘Cherokee Purple’ × ‘Maxifort’ and nongrafted controls in 1.85-m2 media grow beds with hydroponic and aquaponic systems using copper nose bluegill in a greenhouse. Grafting increased stem diameter, leaf count, stem height, flower count, and bud count compared with nongrafted plants. In aquaponics, grafting increased the phosphorus uptake over nongrafted plants grown in the aquaponic system. Grafting resulted in greater fresh (49.2%) and dry (40.0%) shoot biomass, and fresh (33.3%) and dry (42.8%) root biomass. Grafting also increased the uptake of copper and sulfur in the aquaponic systems. The hydroponic systems resulted in greater leaf count, soil plant analysis development, stem height, shoot biomass, and greater boron, phosphorus, potassium, iron, and manganese levels than aquaponic systems. Total fruit number and weight were greater in hydroponic systems than in aquaponic systems by 35.4% and 30.4%, respectively, but fruit splitting was a problem in both. Aquaponics resulted in greater root fresh weight than hydroponics. The nutrients zinc and copper increased with the use of aquaponic systems over hydroponic systems. This research suggests that the type of system can affect growth and nutrient uptake, and ‘Cherokee Purple’ should not be used in a soilless system because of excessive fruit splitting, leading to unmarketable fruit and low yield, unless environmental conditions can be managed during the heat of the summer.

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Abstract

‘Salad Bowl’ and ‘Waldmann’s Green’ leaf lettuce (Lactuca sativa L.) were exposed to photosynthetic photon flux densities (PPFD) of 444 or 889 µmol s–1m–2 for 20 hours day–1 under a diurnal temperature regime of 25°C days/15° nights or 20° days/15° nights. Leaf dry weight of both cultivars was highest under the high PPFD/warm temperature regime and lowest under the low PPFD/cool temperature regime. ‘Waldmann’s Green’ yielded more than did ‘Salad Bowl’ at 889 µmol s–1m–2 and 25° days/20° nights. Under high PPFD, both cultivars yielded better with 25° days/25° nights than with 25° days/20° nights, although relative growth rates were the same under both temperature regimes.

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Greenhouse production of high-quality young annual bedding plants (plugs) at northern latitudes often requires supplemental lighting to compensate for a low natural daily light integral (DLI), but radiation interception by plugs is limited by a low leaf area index. Some species show an increase in leaf area in response to growth under a low ratio of red to far-red radiation (R:FR), and an early increase in leaf area may allow for more effective radiation capture by seedlings and a reduction in wasted radiation. Thus, the objective of this study was to examine the effects of end-of-day far-red (EOD-FR) radiation treatments varying in intensity, R:FR (600–700 nm/700–780 nm), and duration on early leaf expansion and plug quality for petunia (Petunia ×hybrida) ‘Wave Purple’ and ‘Dreams Midnight’. Seedlings were grown in 128-cell trays in a common greenhouse environment under a simulated winter DLI (∼5.3 mol·m−2·s−1) and received one of four EOD-FR treatments, control conditions (no EOD-FR or supplemental lighting), or supplemental lighting (target photosynthetic photon flux density of 70 μmol·m−2·s−1). The EOD-FR treatments were provided for 3 weeks on cotyledon emergence and included the following: 10 μmol·m−2·s−1 of far-red radiation for 30 minutes with a R:FR of ∼0.8 (EODFL), 10 or 20 μmol·m−2·s−1 of far-red radiation for 30 minutes with a R:FR of ∼0.15 (EOD10:30 and EOD20:30, respectively), or 20 μmol·m−2·s−1 of far-red radiation for 240 minutes with a R:FR of ∼0.15 (EOD20:240). Destructive data were collected 14 and 21 days after cotyledon emergence. Seedlings that received EOD-FR treatments did not show any increase in leaf area compared with control or supplemental lighting treatments. Stem length generally increased under EOD-FR treatments compared with supplemental lighting and control treatments; greater elongation was observed when the R:FR decreased from 0.8 to 0.15, and when treatment duration increased from 30 minutes to 240 minutes. However, at a R:FR of 0.15 and a treatment duration of 30 minutes, an increase in far-red radiation intensity from 10 to 20 μmol·m−2·s−1 did not promote further stem elongation resulting in similar stem lengths for both cultivars under EOD10:30 and EOD20:30. Results of this study indicate that under low DLIs, EOD-FR radiation applied in the first 3 weeks of seedling production does not promote early leaf area expansion, and generally decreases seedling quality for petunia. As responses to far-red radiation may vary based on study taxa, incident radiation, and DLI, future research examining EOD-FR–induced morphological changes is warranted.

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Multilayer vertical production systems using sole-source (SS) lighting can be used for the production of microgreens; however, traditional SS lighting methods can consume large amounts of electrical energy. Light-emitting diodes (LEDs) offer many advantages over conventional light sources, including high photoelectric conversion efficiencies, narrowband spectral light quality (LQ), low thermal output, and adjustable light intensities (LIs). The objective of this study was to quantify the effects of SS LEDs of different light qualities and intensities on growth, morphology, and nutrient content of Brassica microgreens. Purple kohlrabi (Brassica oleracea L. var. gongylodes L.), mizuna (Brassica rapa L. var. japonica), and mustard [Brassica juncea (L.) Czern. ‘Garnet Giant’] were grown in hydroponic tray systems placed on multilayer shelves in a walk-in growth chamber. A daily light integral (DLI) of 6, 12, or 18 mol·m−2·d−1 was achieved from commercially available SS LED arrays with light ratios (%) of red:green:blue 74:18:8 (R74:G18:B8), red:blue 87:13 (R87:B13), or red:far-red:blue 84:7:9 (R84:FR7:B9) with a total photon flux (TPF) from 400 to 800 nm of 105, 210, or 315 µmol·m−2·s−1 for 16 hours. Regardless of LQ, as the LI increased from 105 to 315 µmol·m−2·s−1, hypocotyl length (HL) decreased and percent dry weight (DW) increased for kohlrabi, mizuna, and mustard microgreens. With increasing LI, leaf area (LA) of kohlrabi generally decreased and relative chlorophyll content (RCC) increased. In addition, nutrient content increased under low LIs regardless of LQ. The results from this study can help growers to select LIs and LQs from commercially available SS LEDs to achieve preferred growth characteristics of Brassica microgreens.

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Multilayer vertical production systems using sole-source (SS) light-emitting diodes (LEDs) can be an alternative to more traditional methods of microgreens production. One significant benefit of using LEDs is the ability to select light qualities that have beneficial impacts on plant morphology and the synthesis of health-promoting phytochemicals. Therefore, the objective of this study was to quantify the impacts of SS LEDs of different light qualities and intensities on the phytochemical content of brassica (Brassica sp.) microgreens. Specifically, phytochemical measurements included 1) total anthocyanins, 2) total and individual carotenoids, 3) total and individual chlorophylls, and 4) total phenolics. Kohlrabi (Brassica oleracea var. gongylodes), mustard (Brassica juncea ‘Garnet Giant’), and mizuna (Brassica rapa var. japonica) were grown in hydroponic tray systems placed on multilayer shelves in a walk-in growth chamber. A daily light integral (DLI) of 6, 12, or 18 mol·m−2·d−1 was achieved from SS LED arrays with light ratios (percent) of red:blue 87:13 (R87:B13), red:far-red:blue 84:7:9 (R84:FR7:B9), or red:green:blue 74:18:8 (R74:G18:B8) with a total photon flux from 400 to 800 nm of 105, 210, or 315 µmol·m−2·s–1 for 16 hours, respectively. Phytochemical measurements were collected using spectrophotometry and high-performance liquid chromatography (HPLC). Regardless of light quality, total carotenoids were significantly lower under increasing light intensities for mizuna and mustard microgreens. In addition, light quality affected total integrated chlorophyll with higher values observed under the light ratio of R87:B13 compared with R84:FR7:B9 and R74:G18:B8 for kohlrabi and mustard microgreens, respectively. For kohlrabi, with increasing light intensities, the total concentration of anthocyanins was greater compared with those grown under lower light intensities. In addition, for kohlrabi, the light ratios of R87:B13 or R84:FR7:B9 produced significantly higher anthocyanin concentrations compared with the light ratio of R74:G18:B8 under a light intensity of 315 µmol·m−2·s−1. Light quality also influenced the total phenolic concentration of kohlrabi microgreens, with significantly greater levels for the light ratio of R84:FR7:B9 compared with R74:G18:B8 under a light intensity of 105 µmol·m−2·s−1. However, the impact of light intensity on total phenolic concentration of kohlrabi was not significant. The results from this study provide further insight into the selection of light qualities and intensities using SS LEDs to achieve preferred phytochemical content of brassica microgreens.

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