Enabling Year-round Cultivation in the Nordics-Agrivoltaics and Adaptive LED Lighting Control of Daily Light Integral

High efficacy LED lamps combined with adaptive lighting control and greenhouse integrated photovoltaics (PV) could enable the concept of year-round cultivation. This concept can be especially useful for increasing the production in the Nordic countries of crops like herbaceous perennials, forest seedlings, and other potted plants not native of the region, which are grown more than one season in this harsh climate. Meteorological satellite data of this region was analyzed in a parametric study to evaluate the potential of these technologies. The generated maps showed monthly average temperatures fluctuating from −20 °C to 20 °C throughout the year. The natural photoperiod and light intensity also changed drastically, resulting in monthly average daily light integral (DLI) levels ranging from 45–50 mol·m−2·d−1 in summer and contrasting with 0–5 mol·m−2·d−1 during winter. To compensate, growth room cultivation that is independent of outdoor conditions could be used in winter. Depending on the efficacy of the lamps, the electricity required for sole-source lighting at an intensity of 300 µmol·m−2·s−1 for 16 h would be between 1.4 and 2.4 kWh·m−2·d−1. Greenhouses with supplementary lighting could help start the cultivation earlier in spring and extend it further into autumn. The energy required for lighting highly depends on several factors such as the natural light transmittance, the light threshold settings, and the lighting control protocol, resulting in electric demands between 0.6 and 2.4 kWh·m−2·d−1. Integrating PV on the roof or wall structures of the greenhouse could offset some of this electricity, with specific energy yields ranging from 400 to 1120 kWh·kW−1·yr−1 depending on the region and system design.

Effect of various LED lighting on the growth and development of garden strawberry Fragariaxananassa Duch. and groundcover rose Rosa hybrida L. at greenhouse conditions

The purpose of this study was to determine the role of various LED (light-emitting diode) light units in ensuring high-quality growth and development of plants, as well as to obtain high-quality seedlings of strawberries and ground cover rose. We studied the physiological reactions of garden strawberry (“Melga” variety) and ground cover rose (“Fairy” variety) plants under controlled conditions and obtained the data on the effect of light quality on plant biological productivity, dynamics of growth processes, photosynthesis rate and transpiration. Regardless of the type of studied crops, the tallest plants were obtained under conditions of supplementary lighting by the lamp with blue/green/red ratio in the spectrum 17/29/54 % (option 1) and the lamp with ratio 18/45/37 % (option 2). At the same time, the dry weight of leaves and roots, as well as the biological productivity of strawberry plants in experimental options 1 and 2 exceeded by 41% than in the control plants (under high pressure sodium lamp). For garden strawberry we recommend the LED in the option 2, for the ground cover rose optimal is the option 1.

Supplementary Light with Increased Blue Fraction Accelerates Emergence and Improves Development of the Inflorescence in Aechmea, Guzmania and Vriesea

In protected cultivation, increasing the light level via supplementary lighting (SL) is critical to improve external quality, especially in periods with low light availability. Despite wide applications, the effect of light quality remains understated. In this study, the effect of SL quality and nutrient solution electrical conductivity (EC) on growth and flowering of three bromeliad species was investigated. Treatments included solar light, and this supplemented with R90B10 [90% red (R) and 10% blue (B)], R80B20 (80% R and 20% B), and R70B30 (70% R and 30% B). These were combined with an EC of 1 and 2 dS m-l. Irrespective of the light treatment, the higher EC promoted growth, inflorescence emergence, and development in Aechmea fasciata (Lindl.) Baker, whereas adverse effects were noted in Guzmania and Vriesea. The higher EC-induced negative effect in Guzmania and Vriesea was slightly alleviated by SL. With few notable exceptions, SL exerted limited effects on photosynthetic functionality. Depending on the species, SL improved external quality traits. In all species, SL increased root and inflorescence weight and stimulated biomass allocation to generative organs. It also accelerated inflorescence emergence and promoted inflorescence development. In this way, the time to commercial development stage was considerably shortened. These effects were more prominent at R80B20 and R70B30. Under those conditions, for instance, inflorescence emergence occurred 3–5 weeks earlier than in the control, depending on the species. In conclusion, SL with increased B proportion leads to shorter production period owing to faster emergence and improved development of the inflorescence and is recommended for commercial use.

Enabling Year-round Cultivation in the Nordics - Agrivoltaics and Adaptive LED Lighting Control of Daily Light Integral

High efficacy LED lamps combined with adaptive lighting control and greenhouse integrated photovoltaics (PV) could enable the concept of year-round cultivation and become a feasible option even in the harsh climate of the Nordic countries. Meteorological satellite data of this region was analyzed in a parametric study to evaluate the potential of these technologies. The generated maps showed monthly average temperatures fluctuating from -20°C to 20°C throughout the year. The natural photoperiod and light intensity also changed drastically, resulting in monthly average daily light integral (DLI) levels ranging from 45-50 mol·m-2·d-1 in summer and contrasting with 0-5 mol·m-2·d-1 during winter. To compensate, growth room cultivation independent from outdoor conditions could be used in winter. Depending on the efficacy of the lamps, the electricity required for sole-source lighting at 300 µmol·m-2·s-1 for 16 hours would be between 1.4 and 2.4 kWh·m-2·d-1. Greenhouses with supplementary lighting could help start the cultivation earlier in spring and extend it further into autumn. The energy required for lighting highly depends on several factors such as the natural light transmittance, the light threshold settings and the lighting control protocol, resulting in electric demands between 0.6 and 2.4 kWh·m-2·d-1. Integrating PV on the roof or wall structures of the greenhouse could offset some of this electricity, with specific energy yields ranging from 400 to 1120 kWh·kWp-2·yr-1 depending on the region and system design.

Applications and Development of LEDs as Supplementary Lighting for Tomato at Different Latitudes

High-tech greenhouses and artificial light applications aim to improve food production, in line with one of the sustainable development goals of the UN Agenda 2030, namely, “zero hunger”. In the past, the incandescent lamps have been used for supplementary lighting (SL) at higher latitudes to increase greenhouse production during the dark season. Light-emitting diodes (LED) have been replacing gas discharge and incandescent lamps, and their development is expanding SL applications in different agricultural scenarios (e.g., urban farming, middle latitudes). In fact, recent research on LED applications in Mediterranean greenhouses have produced encouraging results. Since middle latitudes have a higher daily light integral (DLI) than higher latitudes in the dark season and climate conditions influence the installed power load of greenhouses, LED installation and management in Mediterranean greenhouses should be different and less expensive in terms of investment and energy consumption. Accordingly, the aim of this review is to outline the state of the art in LED applications and development, with a focus on latitude-related requirements. Tomato was used as a representative crop.

Effects of LED and HPS lighting on the growth, seedling morphology and yield of greenhouse tomatoes and cucumbers

In an experiment with tomato and cucumber transplants, light units equipped with purpose-built LED arrays were compared with HPS sodium lamps with a power of 600 W and a voltage of 230 V. For both the LED and HPS lamps, the same PAR radiation level was used at the plant height, which was about 70–80 μmol/m2/s in conditions without daylight. The supplementary lighting was carried out for 8 to 24 hours and was switched on during the day when the solar radiation outside the greenhouse was lower than 200 W/m2. The supplementary lighting with the LED and HPS lamps did not have a significant impact on the growth of the tomato and cucumber seedlings and the fresh and dry mass of the tomato and cucumber plants. The plants grown without the additional artificial lighting were significantly smaller in height, had fewer leaves, a smaller spread and produced lower fresh and dry weights. The tomato and cucumber plants grown under the LED lamps had a higher chlorophyll index than those grown under the HPS lamps and without any lighting. The supplementary lighting with the LED lamps increased the early yield of the tomatoes compared to the HPS and control plants but has no effect on the early yield of the cucumbers. Both the LED and HPS lighting significantly increased the total and marketable yield of the tomatoes and cucumbers.

Light and Temperature Control for Greenhouse Plant Growth

Introduction. The article deals with the conditions for growing greenhouse plants. Supplementary lighting supports the process of plant photosynthesis and the microclimate in the greenhouse. The authors suggest the ways to reduce energy consumption in greenhouses by controlling the microclimate and process of supplementary lighting in greenhouses. Materials and Methods. Special lighting and temperature are required for growing greenhouse plants. A method of efficient plant growing is light and temperature control. The development of a control algorithm requires the mathematical models that relate the process of photosynthesis to the microclimate parameters. There are given the mathematical models based on the experimental data. Results. The control system and algorithm to control plant-growing conditions have been developed to maintain the greenhouse microclimate. LED lamps are used to control the lighting process. The authors present the developed block diagram of the control system, which contains four channels responsible for the main energy-intensive microclimate factors. The description of the algorithm of the greenhouse light-temperature control is given. Discussion and Conclusion. In conclusion, the need to maintain the greenhouse microclimate and supplementary lighting with the different radiation spectrum for the efficient cultivation of greenhouse plants is shown. The developed structure and control algorithm for the supplementary plant lighting process and greenhouse illumination through using LED lamps help reduce energy consumption.

Acclimation to Ex Vitro Conditions in Ninebark

Acclimation is the final phase of micropropagation and often decisive for its economic output. The aim of the experiments was to evaluate the effect of abscisic acid (ABA) and supplementary light on acclimation and leaf anatomy of the in vitro-rooted plants of ninebark (Physocarpus opulifolius L.). The initial material came from 8–10-week-old in vitro cultures on ½MS supplemented with 1 mg·L−1 IBA. After potting, plantlets were sprayed with ABA solutions or distilled water and were grown either under natural daylight or under supplemental sodium light at 230 μmol·m−2·s−1 between 2 and 9 p.m. All measurements and anatomical observations were done after eight weeks in the greenhouse. Supplementary lighting significantly increased the percentage of acclimatized plants, plant height and the internode number. Plant growth was also positively affected by 1 mg·L−1 ABA. During acclimation, the photosynthesis rate increased while the transpiration and stomatal conductance dropped. The assimilation pigment contents increased under supplemental lighting while ABA had no detectable effect. However, relative to water controls, ABA increased photosynthesis, reduced transpiration, and stomatal conductance in plants growing under both light conditions. Leaves from the in vitro plants were about two times thinner than those from plants growing in soil, with only a single layer of the palisade parenchyma, hence with lower proportion in relation to the spongy parenchyma. Supplementary light during acclimation increased leaf thickness but only in the water control while it decreased it in the ABA-treated plants. ABA increased the mesophyll thickness but only in plants growing under natural light. In conclusion, supplementary light and treatment with ABA enhance acclimation of micropropagated ninebark plants.