LIGHT IS THE primary source of energy required for the photosynthetic process and many other physiological processes related to plant growth, biomass and bioactive medicinal compounds. The growth and development of plant morphology such as leaf anatomy, flowering, height, branching as well as natural products like pigments, essential oils and vitamins are influenced by different light environments including intensity, duration of exposure, quality (colour and wavelength of light) and position of light source (Kozai, 2016).
Prototypes of modular plant cultivation units under different LED spectrums.
What this means is that the quality and growth of plants can be controlled through variations in the light environment including the use of an artificial light source. For this purpose, light-emitting diodes (LEDs) have advantages over traditional sources such as fluorescent lights; they produce less heat and therefore conserve more energy, have a longer lifespan and produce no ultraviolet (UV) emissions which can injure the plants.
Plants respond to different light wavelengths via photoreceptors (Higuchi and Hisamatsu, 2016; Gupta and Agarwal, 2017). Generally, plant pigment molecules only absorb light in the photosynthetically-active radiation (PAR) range, which is a wavelength range of 400nm to 700nm. For instance, a blue-red spectrum falling in the range of 450nm and 650nm wavelengths is the chlorophyll-preferred region for plants to carry out photosynthesis to produce food. Each light wavelength within the visible light spectrum – made up of violet, blue, green, yellow and red regions – can bring certain positive responses in plants.
In this sense, LEDs which are available in many light qualities and intensities can be easily controlled according to the requirements of each plant genotype to establish the optimal condition for the total plant growth rate, morphology, metabolism, nutritional quality and total biomass accumulation.
In recent years, there has been increasing interest in using artificial lighting technology to enhance greenhouse and indoor crop production. Verkerke et al. (2014) established an indoor crop production system by using red and blue LEDs for commercial growers to produce plants with more nutritional benefits. Various LED light treatments have been found to improve vitamin C content in leafy vegetables, increase the amount of antioxidants in plants, enhance fruit colour and accelerate the ripening of fruits (Hao et al. 2014; Alcock and Bertling, 2012). This technology similarly improves the profitability of producers, particularly by exploiting the prices of off-season fruits and vegetables.
Furthermore, some interesting reports have recently appeared about the applications of various LED spectrums on the integrated pest management (IPM) system to control plant pathogens, produce disease-resistant plants, develop antibacterial drugs, and reinforce plant cell walls through elevation of lignin concentrations. Greenhouse crops such as tomatoes, cucumbers, strawberries and potatoes are often plagued by physiological disorders such as abnormal outgrowths on the leaf, petiole and stem. The usage of LEDs has also been shown to limit these effects.
Instead of the familiar scene of crops growing in neat rows on hectares of land in the countryside, one can now visualise a sea of plants growing under controlled artificial lighting that is interspersed between stacks of crops in concrete buildings. Commonly known as vertical farming or the indoor farming system, cities around the globe are cultivating greeneries in urban areas inside and on buildings. Plants that are grown indoors obtain constant lighting from LEDs instead of being exposed to natural light cycles and weather patterns. This enhances growth throughout the year while ensuring that supply keeps up with demand.
The Plant Biotechnology-LED research group is led by Prof Dr. Sreeramanan Subramaniam from the School of Biological Sciences (second from right), USM, post-doctoral fellow Dr. Safiah Ahmad Mubbarakh, Yeow Lit Chow and Eyu Chan Hong (PhD candidates) and Chew Hong Lim (MSc candidate).
It is predicted that by 2025, vertical farming on “farm scrapers” will cater to urban dwellers in developing countries in Africa, Asia and Latin America. In comparison to conventional agriculture, crop production on a 100m-high building with a basal area of five acres is almost equivalent to that from a 2,400-acre old-fashioned farm (Baudoin, 2013). Indoor farming also provides consumers with fresh supplies due to the closer geographic proximity to the end-user.
While such facilities require some forethought and planning in terms of facility space, crop type, scale of operation, ease of LED installation and costs, there is an upward trend among growers around the world to fully adopt energy-efficient LED technology for indoor farming. Of course, additional research is still required to analyse the interactive control of environmental conditions while taking into consideration the running costs and efficient use of resources. But as of now, countries are looking to LED lighting for indoor farming as an economical solution to agriculture in urban areas.
Sreeramanan and some of his research team members during a sharing session with Nobel Laureate Prof Shuji Nakamura on “Invention of Blue LEDs and Future Solid-State Lighting” at the Institute of Nano Optoelectronics Research and Technology (INOR), USM.
Penang Island to Join the Vertical Farming Boom
Penang Island encompasses an area of 293km2, with a population density of 2,465.5/km2. Most of the land is allocated for infrastructure, urban and rural planning. According to research by Penang Institute (2018), agricultural land use in Penang for fruit production steadily decreased from 7,149.8 hectares in 2009 to 3,660.2 hectares in 2017. Meanwhile, land allocated by the Penang state for vegetable production increased only minimally from 489.4 to 688.5 hectares between the same years. In order to increase the state’s self-sufficiency level in agricultural products and to encourage sustainable forms of farming, vertical farming has been cited as a method that supports effective land management and crop productivity.
Penang already has ambitions to become the first Malaysian state to have 100% LED street lighting. Therefore, progression from traditional agriculture to adapting next-generation LED-fitted vertical farming is only logical as a cost-effective and sustainable solution, especially when the growing population necessitates more property development, and arable land becomes inevitably scarcer.
Acknowledgement: The authors would like to thank the Collaborative Research in Engineering, Science and Technology Centre (CREST), and Universiti Sains Malaysia (USM) for supporting this research study.
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