Crop production in open fields is increasingly limited by weather extremes and water shortages, in addition to pests and soil-borne diseases. In order to increase crop yield, quality, and productivity, controlled environment agriculture (CEA) can play an important role as an alternative and supplemental production system to conventional open field production. CEA is any agricultural technology that enables growers to manipulate the growing environment for improved yield and quality. CEA production systems include high tunnels, greenhouses, and indoor vertical farming, as well as hydroponics and aquaponics. Currently, ‘low-tech’ CEA techniques such as high tunnels (plastic greenhouses with minimum or no cooling and heating) are primarily utilized in developing countries where labor costs are relatively low, and China has by far the largest area covered by high tunnels or ‘Chinese-style’ solar greenhouses. The most control-intensive ‘high-tech’ CEA approach, namely indoor vertical farming, has gained tremendous attention in the past decade by researchers and entrepreneurs around the world, owing to advancements in lighting technology, including use of light emitting diodes (LEDs), and increasing urbanization with new market opportunities. This special issue covers some of the CEA topics such as LED lighting, substrate, and hydroponics. Full article

The objective of this study was to characterize growth, water-use efficiency (WUE), stomatal conductance (g_s), SPAD index values, and shoot nitrogen uptake of two lettuce cultivars grown under different percentages of blue and red light. The treatments evaluated were 100% red; 7% blue + 93% red; 26% blue + 74% red; 42% blue + 58% red; 66% blue + 34% red; and 100% blue. Broad-spectrum (19% blue, 43% green, and 38% red) light was used to observe the effects of wavelength interactions. All of the treatments provided an average daily light integral (DLI) of 17.5 mol·m^‒2·d^‒1 (270 ± 5 µmol·m^‒2·s^‒1 over an 18-h photoperiod). The experiment was replicated three times over time; each terminated 21 days after treatment initiation. Leaf area, specific leaf area (SLA), and SPAD index had a similar response in that all of the parameters increased with up to 66% blue light, and slightly decreased or remained constant with 100% blue light. In contrast, leaf number, shoot dry mass, and WUE generally decreased in response to blue light. Conversely, for every 10% increase in blue light, g_s increased by 10 mmol·m^‒2·s^‒1. Nitrogen uptake was unaffected by light quality. Our findings indicate that when grown under different blue and red photon flux ratios, the WUE of lettuce significantly decreases under higher blue light, which could be attributed to a reduction in plant growth (leaf number and dry mass), and an increase in g_s. However, green light within broad-spectrum lamps might counteract blue-light mediated effects on g_s and WUE in lettuce. Full article

Lettuce is an economically important crop for small and medium-sized growers. When grown in adverse environmental conditions, lettuce is vulnerable to a deterioration of yield and quality. Research concerning the impact of elevated potassium (K) levels on leafy vegetables, such as lettuce, is lacking. Therefore, seeds of dark-red ‘Lollo’ lettuce were germinated under greenhouse conditions at 25/20 °C (day/night). Plants were transferred into 11-L containers and placed into growth chambers at 25 and 33 °C. Plants were grown with K treatments of 117.3 (control), 234.6 (2×), 469.2 (4×), and 4) 938.4 (8×) mg·L⁻¹. Increasing K treatments resulted in a negative quadratic response on lettuce dry mass and generated 14% more leaf calcium at 234.6 mg·L⁻¹. An increase in temperature from 25 to 33 °C increased leaf dry matter and biomass by 40% and 43%, respectively. Leaf water content increased by 3% as temperature increased. Plants grown at 33 °C had greater quercetin glycosides compared to plants grown at 25 °C. The results from this study suggest that temperature is a stronger regulatory factor than increasing K in the determination of lettuce yield and quality. Increasing K concentration to 234.6 mg·L⁻¹ results in greater concentrations of leaf minerals without compromising plant yield. Full article

In Puerto Rico, oranges made up $6,452,000 of the agricultural gross income for 2014–2015. Today, citrus greening (CG) is the most aggressive disease affecting the citrus industry in the whole world. This disease causes dieback of the plant, among other symptoms, which is resulting in the reduction of citrus trees in the field across the world. Currently, it is recommended to grow citrus rootstocks in nurseries to produce disease-free trees. The objective of this investigation was to evaluate (before and after grafting) the effect of different substrate mixes and quantities of fertilizers on the rootstocks Carrizo citrange and Swingle citrumelo in order to accelerate their development inside of a protected structure. The treatments were: Promix + sand (control) (1:1), Promix + sand + coco peat (1:1:1), Promix + sand + coffee compost (1:1:1) and Promix + sand + rice husk (1:1:1). Two 18-6-2 fertilizer treatments were also evaluated: 5.6 g and 8.5 g. The substrate that contained 33% rice husks negatively influenced every parameter evaluated for both rootstocks. Carrizo presented better development on the coffee compost mix, while Swingle did not exhibit significant differences among any substrates, except on rice husk, for most of the parameters. “Rhode Red Valencia” presented better results for dry weight when grafted on Carrizo with the coffee substrate. The rice husk substrate is not recommended for the citrus tree production at the nursery level. Full article

The objective of this study was to evaluate growth and physiological responses of ‘Cherokee’ and ‘Waldmann’s Green’ lettuce (Lactuca sativa) exposed to small changes in light quality and intensity within a 24-h period. Three pre-dawn (PD; 0600 to 0700) and three end-of-day (EOD; 2100 to 2200) treatments were evaluated in the study, each providing 50 ± 2 µmol·m⁻²·s⁻¹ of either blue, red, or broadband white light from light-emitting diodes (LEDs). To account for the main daily light integral (DLI), broadband white LEDs provided 210 ± 2 µmol·m⁻²·s⁻¹ from 0700 to 2200 or from 0600 to 2100 for the PD or EOD treatments, respectively. A control treatment was included which provided 200 ± 2 µmol·m⁻²·s⁻¹ of white light from 0600 to 2200. All treatments provided a DLI of 11.5 mol·m⁻²·day⁻¹ over a 16-h photoperiod. Regardless of cultivar, no treatment difference was measured for hypocotyl length or leaf number. However, plants grown under EOD-blue or PD-white had up to 26% larger leaves than those grown under PD-red and 20% larger leaves than control. In addition, plants grown under EOD-blue produced up to 18% more shoot fresh mass compared to those grown under control, EOD-red, or PD-red. Contrasts for gas-exchange data collected during the main photoperiod showed that light quality was not significant within PD or EOD for any of the parameters evaluated. However, regardless of light quality, stomatal conductance (g_s) and transpiration (E) were up to 34% and 42% higher, respectively, for EOD-grown plants compared to control. Our results suggest that 1 h of low intensity EOD-blue light has the potential to promote lettuce growth by increasing leaf area and shoot fresh mass when the main DLI from sole-source lighting is provided by broadband white LEDs. Full article

Two greenhouse experiments were conducted to examine the growth and mineral nutrition of four leafy vegetables in a nutrient film technique (NFT) system with water with low to moderate salinity. In Expt. 1, a nutrient solution was prepared using reverse osmosis (RO) water and treatments consisted of supplementing with RO water, tap water, or nutrient solution. In Expt. 2, nutrient solution was prepared using three different water sources (treatments), namely, RO water, tap water, or tap water, plus sodium chloride (NaCl), and supplementing solution was prepared using the same three water sources at one third strength. For both of the experiments, seeds of pac choi ‘Tokyo Bekana’, ‘Mei Qing Choi’, and ‘Rosie’ (Brassica rapa var. chinensis) and leaf lettuce ‘Tropicana’ (Lactuca sativa) were sown and were grown in a growth chamber. Two weeks after sowing, seedlings were transplanted to the NFT systems. Expt. 1 was conducted from 19 April to 19 May 2016 and Expt. 2 from 6 September to 12 October 2016. In Expt. 1, nitrate (NO₃⁻) and phosphorus (P) levels in the tanks decreased, and potassium (K⁺) levels reached almost zero at the end of the experiment when supplemented with RO or tap water. However, calcium (Ca²⁺), magnesium (Mg²⁺), and sulfate (SO₄²⁻) either did not decrease or increased over time. Supplementing water type did not affect the growth of leaf lettuce and ‘Mei Qing Choi’ pac choi; however, fresh weight of ‘Rosie’ pac choi and both fresh and dry weight of ‘Tokyo Bekana’ pac choi were reduced when supplemented with RO water. Leaf sap NO₃⁻ was reduced in ‘Tokyo Bekana’ pac choi, but not in other varieties, when supplemented with RO or tap water. Leaf sap K⁺ decreased in ‘Tokyo Bekana’, but not in other varieties. The supplementing water type did not impact leaf sap Ca²⁺, regardless of vegetable varieties. In Expt. 2, NO₃⁻ in all of the treatments, P in RO water, and K⁺ in RO or tap water decreased in the last week of the experiment. Other macronutrients did not change substantially over time. The addition of NaCl significantly reduced the growth of all the vegetables. ‘Tropicana’ leaf lettuce was the least tolerant to NaCl, followed by ‘Rosie’ pac choi. Water source did not affect leaf Ca²⁺, K⁺, P, SO₄²⁻, and Mg²⁺ except for ‘Tokyo Bekana’ where NaCl addition decreased Ca²⁺ and Mg²⁺. Our results indicated that the tested leafy vegetables differed in response to various types of water used as supplementing or as source water. N, P, and especially K, should be supplemented in the late stage of the experiment, while replacing the whole tank nutrient solution is only necessary when Na⁺ and/Cl⁻ build up to harmful levels. Full article

A greenhouse study was conducted to evaluate the growth and development of poinsettia ‘Prestige Red’ (Euphorbia pulcherrima) grown in a commercial peat-based potting mix (Sunshine Mix #1) amended with biochar at 0%, 20%, 40%, 60%, 80%, or 100% (by volume) at four different fertigation regimes: F1: 100 to 200 mg·L⁻¹ nitrogen (N), F2: 200 to 300 mg·L⁻¹ N (control), F3: 300 to 400 mg·L⁻¹ N, or F4: 400 to 500 mg·L⁻¹ N. The experiment was a two-factor factorial design with 10 replications for each combination of biochar by fertigation. As the percentage of biochar increased, root substrate pore space and bulk density increased, while container capacity decreased. Root rot and red bract necrosis only occurred in F4 combined with 100% biochar. Plants grown in 40% biochar had a similar growth and development to those in 0% biochar. Up to 80% biochar, plants exhibited no significant change, except in terms of dry weight, which decreased at higher biochar percentages (60% and 80%). In summary, at a fertigation rate of 100 mg·L⁻¹ N to 400 mg·L⁻¹ N, up to 80% biochar could be used as an amendment to peat-based root substrate with acceptable growth reduction and no changes in quality. Full article

In recent years, consumption of herb products has increased in daily diets, contributing to the prevention of cardiovascular diseases, chronic diseases, and certain types of cancer owing to high concentrations of phytonutrients such as essential oils and phenolic compounds. To meet the increasing demand for high quality herbs, controlled environment agriculture is an alternative and a supplement to field production. Light is one of the most important environmental factors influencing herb quality including phytonutrient content, in addition to effects on growth and development. The recent development and adoption of light-emitting diodes provides opportunities for targeted regulation of growth and phytonutrient accumulation by herbs to optimize productivity and quality under controlled environments. For most herb species, red light supplemented with blue light significantly increased plant yield. However, plant yield decreased when the blue light proportion (BP) reached a threshold, which varied among species. Research has also shown that red, blue, and ultraviolet (UV) light enhanced the concentration of essential oils and phenolic compounds in various herbs and improved antioxidant capacities of herbs compared with white light or sunlight, yet these improvement effects varied among species, compounds, and light treatments. In addition to red and blue light, other light spectra within the photosynthetically active region—such as cyan, green, yellow, orange, and far-red light—are absorbed by photosynthetic pigments and utilized in leaves. However, only a few selected ranges of light spectra have been investigated, and the effects of light quality (spectrum distribution of light sources) on herb production are not fully understood. This paper reviews how light quality affected the growth and phytonutrient accumulation of both culinary and medicinal herbs under controlled environments, and discusses future research opportunities to produce high quantity and quality herbs. Full article