Plant factory with artificial light: pros and cons

The extensive environment, especially low temperature and weak lighting in winter and spring, which limits the growth of pepper (Capicum annuum L.) seedlings, the use of plant factory with artificial lighting technology can effectively control the lighting environment to produce high-quality seedlings. In this study, white LED lamps with R:B ratio of 0.7 (L0.7) and 1.5 (L1.5) and red-blue LED lamps with R:B ratio of 3.5 (L3.5) were used to cultivate seedlings of “CAU-24” pepper in the light intensity of 250 μmol/m2·s and photoperiod of 12 h/d, white fluorescent lamps with R:B ratio of 1.7 (F1.7) was used as control. The results showed that plant height, stem diameter, hypocotyl length, biomass accumulation, light energy use efficiency (LUE) and electric energy use efficiency (EUE) of pepper seedling under L1.5 were the highest. After 36 days of sowing, the dry weight of shoot reached 302.8±45.2 mg/plant. Leaf area reached maximum value of 153.5±22.0 cm2 under L0.7. The contents of chlorophyll a, chlorophyll b and total chlorophyll of pepper seedling leaves under all kinds of LED light were greater than F1.7, but there was no significant difference in net photosynthetic rate. The total dry weight with lamp electric power consumption of L1.5 were 3.0 g/(kW·h) which was 1.5, 2, and 3 times greater than that of L3.5, L0.7, and F1.7, respectively. Therefore, compared with fluorescent lamp and other LED lamps, the white LED light quality with R:B ratio of 1.5 is suitable for pepper seedling production in plant factory because of the high LED lighting efficiency, greater LUE and EUE. Keywords: pepper seedlings, LED light quality, R: B ratio, light energy use efficiency (LUE), electric energy use efficiency (EUE) DOI: 10.25165/j.ijabe.20191205.4847 Citation: Liu N, Ji F, Xu L J, He D X. Effects of LED light quality on the growth of pepper seedling in plant factory. Int J Agric & Biol Eng, 2019; 12(5): 44–50.

This perspective paper examines the research and development challenges faced by plant factories with artificial lighting (plant factories hereafter). The global and local challenges facing our planet can be divided into the following four categories: (1) food and agriculture; (2) environment and ecosystems; (3) depletion, uneven distribution, and the overuse of nonrenewable resources; and (4) society, economy, and quality of life. All of the aspects of this four-way deadlock problem must be resolved simultaneously, since solving only one of them could exacerbate one or more of the remaining three. In this paper, the role of plant factories in solving the four-way deadlock problem is discussed from the following perspectives: (1) civilization and culture, (2) participatory science, and (3) the integration of biotechnology and the latest nonbiological technology, such as artificial intelligence (AI). The relationship and interactions between the environment and plant ecosystems are easily observed in the plant factories’ cultivation room. Thus, it is easy to analyze their relationship and interactions. The findings from such observations can also be applied to increase the yield in plant factories, with minimum resource inputs. Moreover, if the electricity generated by renewable energy sources is used, it will become an energy-autonomous plant factory. This means that the plant factory can be operated with the minimum contribution of greenhouse gas emissions to global warming and land area use.

A plant factory is a highly developed product system that can produce higher yields and better quality plants under controlled conditions. However, knowledge of blueberry cultivation in plant factories is limited. This study established an advanced plant factory with artificial lighting (PFAL) and investigated the effects of nutrition supply and light qualities on the growth performance of blueberries. Different nutrition treatments affected the vegetative growth of blueberries in PFAL, especially the new shoot length and number. Exogenous fertilization significantly promoted the uptake of N, P, and K elements, and a nutrition solution with N:P:K = 2:1:1 was suggested to be superior for blueberries in PFAL. Red light facilitated vegetative growth to some degree, and the blue light was conducive to increased chlorophyll and anthocyanin content. The Pn value was significantly enhanced under 60% red plus 40% blue light. Combining red and blue light is more beneficial to blueberry growth and might be a preferential strategy in PFAL. This study is the first to investigate the growth performance of blueberries cultivated in PFAL, which can provide an important theoretical database for blueberry cultivation in a plant factory with artificial lighting.

A Plant Factory With Artificial Lighting (PFAL) consiste em um sistema de horticultura protegido em instalações de ambiente controlado, em combinação com vários níveis de superfície de crescimento e associação de fatores como iluminação, sistema de cultivo, nutrição das culturas e eficiência energética. O objetivo deste estudo foi identificar nos artigos científicos publicados os atuais temas abordados, as potencialidades e desafios identificados e seu posicionamento futuro sobre as PFAL. Trata-se de uma revisão de escopo de 49 artigos publicados em periódicos científicos que davam a resposta à pergunta de investigação, “Quais são os temas abordados em artigos científicos sobre PFAL?”, no período de 2015 a 2022. Os artigos revisados demonstraram como tendência o desenvolvimento de alternativas para os métodos de cultivo, sistemas de iluminação com variação do espectro de luz, sistemas de irrigação e novas tecnologias de cadeia produtiva, visando ao aumento da capacidade produtiva. Também mostraram que, embora a PFAL tenha demonstrado potencial para a produção de diversas culturas, a otimização técnica e econômica requer maior atenção, apontando-se que o desenvolvimento tecnológico e os métodos produtivos são fatores fundamentais para ela se estabelecer como alternativa de produção agrícola em centros urbanos sustentáveis.

Construction of a tomato seedling growth model and economic benefit analysis under different photoperiod strategies in plant factories

Environmental and resource use analysis of plant factories with energy technology options: A case study in Japan

Appropriate growth forms for strawberry production in a plant factory with artificial lighting (PFAL), which is a recently developed production system, remain undetermined. Improving strawberry productivity in a PFAL requires insights into the interplay between production characteristics (growth and photosynthesis) and growth forms, such as plant height and leaf area ( LA ), which are major determinants of crop yield. Growth status, yield, and photosynthetic characteristics of the two cultivars of strawberries ( Fragaria × ananassa Duch. Tochiotome and Koiminori) with different growth forms were examined. ‘Koiminori’ exhibited a 1.9-fold higher yield and a 2.0-fold greater total dry weight of respective organs compared with ‘Tochiotome’. The single-plant photosynthetic rate ( A P ), serving as an index for both cultivars, was 2.2-times higher for Koiminori than for Tochiotome. The photosynthetic rates of a single leaf ( A L ) and LA were also analyzed as important factors that influence the A P . The A L for ‘Koiminori’ surpassed that of ‘Tochiotome’ by 1.4 times. This was attributed to the elevated photosynthetic photon flux density received by the upper leaves of Koiminori, which is a consequence of its higher plant height in proximity to the light source. Evaluation of four photosynthetic capacities, maximum rate of carboxylation, maximum rate of electron transport, photosynthetic rate under saturating light, and light utilization efficiency, which are potential factors that affect A L , revealed no differences in these capacities between cultivars. ‘Koiminori’ exhibited a significantly larger LA (2.3- to 3.1-times) than ‘Tochiotome’, indicating that the former’s higher A P resulted mainly from its higher A L and larger LA . Thus, strawberry production in a PFAL can be improved by growing cultivars with growth forms such as higher plant height and larger LA .

Chapter 23 - Toward commercial production of head vegetables in plant factories with artificial lighting

This paper reviews the reasons why plant factories with artificial light are recently interested in society, requirements for sustainable plant factories, the opportunities and challenges involved in the development of the technology and industry, and types of the plants suitable for plant factories with artificial light. Sustainable plant factories need to be designed and operated for producing high quality plants and transplants with minimum use of resource and minimum emissions of CO2 and environmental pollutants. For this purpose, the concept of closed has been proposed, which is a structure with minimum ventilation, covered with thermally insulated opaque walls, containing multi-tiers (or racks) with artificial light sources. Advantages of this system over the greenhouse include: 1) culture period is shortened by 40-50% with uniform growth and high quality produce, 2) annual production capacity per floor area is 100-fold, and 3) percent reductions in resource consumption are considerable. For example, percent reduction is 100% for pesticide and 95% for irrigation water. Electricity consumption for producing one tomato transplant from a seed is about 300-400 kJ and its cost in Japan is about 1 JPY (0.008 Euro or 1 US cent as of 2011), and is 25 JPY for producing one butter head lettuce from a seed. Methods of developing integrative environmental control and reducing electricity consumption are discussed based mainly on theoretical consideration. Effects of environmental factors on the growth and development are beyond the scope of this paper.

In this study, an experiment was conducted to suggest optimal daytime temperature and light intensity for cucumber scion and rootstock production in a plant factory with artificial light. Plant growth of cucumber scions and rootstocks at a day/night temperature of 26/18 °C and photosynthetic photon fluxes of 50, 120, 190, 260, 330, and 400 μmol·m−2·s−1 was investigated. Plant growth under daytime temperatures of 25/18, 26/18, 27/18, and 28/18 °C at a photosynthetic photon flux of 260 μmol·m−2·s−1 was investigated. As the photosynthetic photon flux increased, hypocotyl length was shortened in cucumber scions and rootstocks, but Dickson quality index, compactness, and Seedling Health Index were improved. As the daytime temperature increased, the hypocotyl length of cucumber scions increased, but the quality of seedlings decreased. The root growth of scions decreased as the daytime temperature increased. As for the correlation between the major growth indicators, Dickson quality index, compactness, and Seedling Health Index showed a high correlation of more than 0.8 in stem diameter, leaf, and root weight. Therefore, it is judged that it is most efficient to maintain the photosynthetic photon flux at 260 μmol·m−2·s−1 throughout the year and adjust the daytime temperature to 25 to 28 °C according to the season for farms and commercial nurseries that produce cucumber seedlings by installing plant factories with artificial light.

Chapter 23 - Automated Technology in Plant Factories with Artificial Lighting

The understanding of the supplementation scheme of red (R) and far-red (FR) light in the cultivation of leafy vegetables in plant factories with artificial lighting (PFALs) is still limited. This study investigated the effects of supplemental R and FR light at different plant growth stages on the morphology, growth characteristics, and nutritional properties of lettuce. Supplemented R + FR throughout the entire growth stages was beneficial for the growth of lettuce, for which the total fresh weight was increased by 53.76%, and it also enhanced the content of soluble sugars by 39.98% and vitamin E by 34.21%. The pre-supplementation of FR light followed by supplementation of R light at various growth stages not only increase the total fresh weight of lettuce by 26.10% but also ensured that most nutritional indices did not decrease, and it even increased the content of soluble sugars by 35.24% while decreasing the nitrate content by 31.52%. The scheme of pre-supplementation of R light followed by the supplementation of FR light promoted a more upright plant architecture in lettuce, which was advantageous for improving the cultivation density of lettuce in plant factories with artificial lighting, thereby enhancing the yield/m2. Moreover, it could increase the vitamin E content of lettuce. The growth and nutritional properties of lettuce exhibit significant effects under different supplementation methods of R and FR light. In PFALs, the selection of different light supplement schemes also requires a careful balance between yield and quality. From an energy-saving perspective, the pre-supplementation of FR light followed by supplementation of R light at various plant growth stages is beneficial for lettuce production in PFALs.

Airflow plays a crucial role in plant growth because it supplies CO2, O2, and energy to plants in a plant factory with artificial light (PFAL). Therefore, understanding how various factors affect airflow in and around a plant canopy is essential. In this study, we developed a computational fluid dynamics (CFD) model with realistic plant structures created using structure-from-motion imaging to investigate airflow in and around a plant canopy. The averages of the absolute percentage errors of simulated air velocity in three conditions were 6.7%, 10.1%, 12.7%, respectively. The simulated and measured air velocities agreed well, confirming the accuracy of the developed CFD model. The effects of inflow velocities and plant canopy structures on the airflow in and around the plant canopy were analysed using the validated CFD model. The inflow velocities significantly decreased stagnant zones (from 62.4% to 7.2%) and increased the airflow uniformity in and around the plant canopy. A staggered layout of the plant canopy slightly decreased stagnant zones (from 16.4% to 13.2%) and increased the airflow uniformity. The airflow in and around the plant canopy was further inhibited by a large plant structure. This CFD model provided a basis for improving the airflow status in and around a plant canopy in a PFAL.

Lettuce (Latuca sativa L.) is a commercially important crop and a good candidate for production in a plant factory with artificial lighting (PFAL). To explore the influence of CO2 enrichment (eCO2) on lettuce growth, light‐use efficiency (LUE) and various aspects of the growth indicators were specifically assessed. Three CO2 concentrations ([CO2]): ambient CO2 (as the control, approximately 400 μmol mol−1), approximately double the ambient (DA‐CO2, 800 ± 50 μmol mol−1), and approximately quadruple the ambient (QA‐CO2, 1600 ± 50 μmol mol−1) were applied for 30 d. The results indicated that plant height, stem diameter, number of leaves, root length, leaf width, and maximum leaf area were all positively related to [CO2], which illustrated that growth was greater in the treatments with eCO2 than under ambient CO2. The daily average assimilation rate (DAAR), the average dry weight growth rate (GRdw), and yield were also greater for plants grown under DA‐CO2 and QA‐CO2 than under ambient CO2 (DAAR increased by 25.45% and 42.27%, GRdw increased by 28.76 and 37.55%, and yield increased by 33.65 and 44.16%, respectively). Light‐use efficiency increased by 28.51 and 41.12% for DA‐CO2 and QA‐CO2 compared with ambient CO2, respectively. We concluded that eCO2 has the potential to enhance production as well as light utilization in PFAL.

Simple SummaryToday, Panax ginseng C. A. Meyer, which has high economic value, is cultivated for the purpose of using the shoot as well as the root, which is better known as the medicinal properties. However, when ginseng is grown outdoors, the quantity and quality of the crop are negatively affected by the climatic environment. In this study, we compared and analyzed the physiological and growth responses of P. ginseng under different LED spectra in a plant factory to achieve continuous and increased productivity. Red and yellow light effectively increased shoot biomass, whereas white light effectively increased root biomass. Furthermore, the intercellular CO2 partial pressure was identified as the most significant physiological variable contributing to root production. Research on light spectra in controlled environments can provide insights into increasing P. ginseng production and contribute to the understanding of the physiological and growth responses of shade-tolerant plants such as P. ginseng.To identify effective light spectra for increasing the productivity of Panax ginseng, we conducted experiments in a controlled environment using a hydroponic cultivation system in a plant factory. We investigated the effect of single LEDs (red, blue, and yellow) and mixed LEDs (red + blue and red + blue + white). The relationships between four light spectra (red, blue, yellow, and white) and physiological responses (net photosynthetic rate, stomata conductance, transpiration rate, and intercellular CO2 partial pressure), as well as growth responses (shoot and root biomass), were analyzed using multivariate statistical analysis. Among the four physiological response variables, shoot biomass was not increased by any pathway, and root biomass was increased only by the intercellular CO2 partial pressure. Red and yellow light increased shoot biomass, whereas white light promoted an increase in the net photosynthetic rate and enhanced root biomass. In contrast, blue light was less effective than the other light spectra in increasing both shoot and root biomass. Therefore, red and yellow light are the most effective light spectra for increasing shoot biomass and white light is effective for increasing root biomass in a plant factory that uses artificial LED lighting. Furthermore, the intercellular CO2 partial pressure is an important physiological variable for increasing the root biomass of P. ginseng.