Vertical farming - smart urban agriculture for enhancing resilience and sustainability in food security

ABSTRACT

Global food security has been significantly threatened by the Covid-19 pandemic and several prolonged challenges such as climate change, population increases, shortage of natural resources, energy crisis, and rapid urbanisation worldwide. Although numerous attempts have been made to secure resilience in the food system, many countries are suffering from hunger and malnutrition, particularly in African and some Asian countries. This review paper presents one of the sustainable farming practices – vertical farming that could play a key role in mitigating global food security in the current uncertain world. It addresses the recent development of vertical farming with advanced precision monitoring and controlling system by the Internet of Things (IoT) applications. It also provides information about the opportunities and challenges of vertical-urban agriculture and how urban agriculture meets economic, social and educational needs.

KEYWORDS:

• Vertical farming
• smart farming
• urban agriculture
• hydroponic
• aeroponic

Introduction

Global food security has been significantly threatened by the Covid-19 Pandemic along with the prolonged drivers of food insecurity including climate change, shortage of agricultural resources, an energy crisis, an increase in population, and urbanisation (Oh et al., 2021). Land/soil degradation is a particularly serious issue for global food security highly affecting the scarcity of arable land for crop production. Reduction in the global land area will require a 50 to 100% increase in food production per unit hectare on existing land by 2050 (Searchinger et al., 2018). Many countries depending on imports for their food supplies are struggling to afford food and there are less choices for healthy food due to their higher prices and insecurity of accessibility (Hardy et al., 2021). Therefore, we urgently need to rethink the way we farm.

Vertical farming is a modern agricultural practice of growing crops, stacked vertically in a protected indoor environment, which mainly utilises a hydroponic or aeroponic cultivation system. Vertical farming offers numerous potential benefits, including more efficient uses of space, reduced water usage, shorter growing times, reduced need for pesticides/herbicides, and shelter from extreme weather. In addition, since vertical farms can be set up practically anywhere, even underground, they could enable hyper-localised production, thus shortening food supply chains and providing fresh and nutritious local foods all year around (Eldridge et al., 2020; Shamshiri et al., 2018).

This review paper aims to review the recent development of vertical farming-smart urban agriculture. The objectives are to (i) present the current development of vertical farming and urban agriculture worldwide; (ii) determine state-of-the-art of vertical farming with modern and precision technologies; and (iii) identify current challenges and opportunities of vertical farming for food security.

Vertical farming: mitigation for food security

Urbanisation has continuously increased worldwide and 55% of the world’s population inhabits urban areas. Whilst the population of rural areas residents is expected to drop by 11% in 2030, the number of urban settlements will be continuously increased (United Nations [UN], 2018). As the demand for food supply in city residents has increased, smart urban-vertical farming has been highlighted. Urban agriculture mitigates societal, environmental and economic challenges related to food security owing to controlled and optimal growing conditions such as temperature, humidity, CO₂ and lighting conditions. It eventually contributes to shortening the growing cycle and increasing plant density and enhancing harvest yield (Khan et al., 2020; Treftz & Omaye, 2016). Owing to urban accessibility, urban agriculture alleviates energy and expenses for transportation, distribution and storage management, and enables the reduction of the carbon footprint of food crops (Avgoustaki & Xydis, 2020b).

According to Armanda et al. (2019), several countries in Europe and Asia and the United States of America have been practising commercialised vertical farming systems. Unlike conventional controlled environmental agriculture such as glasshouse cultivation with natural sunlight, indoor vertical farming is based on fully controlling and monitoring the growing condition including artificial light sources with a high yield in less space. Farms vary in location, such as underground, in abandoned areas or on rooftops, reflecting that each farm applies distinctive technologies for specific microenvironments. Overall, urban agricultural farms focus on growing leafy vegetables with a high annual food production (Armanda et al., 2019). Vertical farming has been widely employed in East and Southeast Asian countries, including China (e.g. Smart farm in Fujian Province), Japan (e.g. Nuvege Plant Factory), Singapore (e.g. Sky Green Farms) and South Korea (e.g. NextOn) (Shamshiri et al., 2018). In North America, the USA and Canada feature several urban farm projects (e.g. AeroFarms). The AeroFarms is based in New Jersey and it is one of the largest indoor vertical farms in the world with 8400 square metres of growing space using an aeroponic growing system (Hardy et al., 2021).

Because of the significant rate of urbanisation, urban agriculture is rapidly developing and practised in Asian countries. However, there are several challenges to its implementation in Asia. For instance, there is a lack of arable areas in urban or peri-urban regions and significant requirements for residential areas as opposed to urban farms. Varying legislation and regulations in different regions also hinder the urban agriculture development (Akaeze & Nandwani, 2020). Although urban agriculture faces several challenges, numerous examples have shown that urban agriculture not only delivers food crops successfully but also provides socioeconomic benefits, including environmental (e.g. provision of biodiversity and sustainability in urban areas) and socioeconomic benefits (e.g. leisure, education and reduction of transportation for food crops) (Akaeze & Nandwani, 2020).

In European countries, urban agriculture is expected to handle the societal transformations of both urban and rural areas, such as ageing and generational renewal in the agriculture (Piorr et al., 2018). There are several successful commercialised urban farms in Northwest European countries including Belgium (e.g. BIGH Farms), France (e.g. Agricool and La Caverne), Germany (e.g. InFarm), the Netherlands (e.g. RotterZwam), Sweden (e.g. Urban Oasis), and the United Kingdom (e.g. Zero Carbon Food Ltd/Growing-Underground, Intelligent Growth Solutions Ltd., Jones Food Company and Fischer Farms (Armanda et al., 2019; Shamshiri et al., 2018; Figure 1).

Figure 1. Indoor vertical farming with the automated controlled system in the UK. (a) via a unique modular and scalable system called total controlled environmental agriculture (TECA), Intelligent Growth Solutions Ltd. use 50% of less energy required by comparable systems for growing vegetables (photo provided by Intelligent Growth Solutions company). (b) Growing-Underground is the first commercial hydroponic farm of Zero Carbon Food Ltd. which utilised the discarded underground shelter in the UK (photo provided by Zero Carbon Food Ltd/Growing-Underground).

The importance of urban agriculture/vertical farming is significant in low- and low-middle-income countries such as in sub-Saharan Africa and parts of Southern Asia. Unlike in high- or high-middle-income countries, urban agriculture has greatly impacted small growers since it is practised for the purpose of self-sufficiency in low- and low-middle-income countries. Therefore, there are relatively few urban agriculture projects on a large scale, such as at the community or national level. However, recent urban agricultural programmes have attempted to enhance food security and mitigate the adverse effects on the environment based on an understanding of the current barriers to urban agriculture, including formal settlement issues, rights of property and distance from urban farms to food retailers (Davies et al., 2020; FAO, 2012).

Vertical farming technologies

There are controversies about the efficiency of vertical farming due to the high initial costs and high maintenance requirements in urban areas. However, by removing the seasonality of growing fresh vegetables, it would be possible to increase yield and profits in vertical farming (Beacham et al., 2019). According to Kozai et al. (2015), indoor vertical farming shows 100 times higher productivity in leafy lettuce compared to conventional cultivation and 15 times that of glasshouse cultivation (Kozai et al., 2015). Vertical farming creates economic benefits not only by increasing yield but also decreasing the expenses for transportation or storage (Van Gerrewey et al., 2022). Farmers in turn will benefit from reduced crop losses, improved yields and more secure supply chains as well as reduced environmental impact and improved agricultural sustainability. Soilless cultivation systems have been improved by subsystem upgrading such as utilising an ultrasonic atomisation system in aeroponics which enables more precise and effective control of the supply of nutrient solution than does the use of water pumps in hydroponic systems. Within the droplet size range (1–5 µm), the ultrasonic atomisation method is significantly impacted by the aeroponic flow rate and temperature of the root zone (e.g. nutrient solution) (Niam & Sucahyo, 2020).

Known as ‘Aeroponic 2.0”, fogponic has been highlighted as a high-energy efficient cultivation system as operates like aeroponics. In the fogponic systems, ultrasonic fog generates fine foggy mist ranging from 5 to 30 μm and it guarantees sufficient oxygen availability for plants by circulating nutrient fog within the air conditioner. Compared to conventional hydroponic and aeroponic systems, fogponics reduces water and fertiliser usage by up to 50% to 60% respectively (Rakib Uddin & Suliaman, 2021; Venkatesh et al., 2020).

Methods of growing plants without soil and soilless cultivation have been widely used in protected agriculture and horticulture and reduced sources of both water and nutrients since the initial application of these approaches. Along with the subsystem development, numerous research articles have been published highlighting technology developments in the optimum growing conditions for indoor vertical farming. The plant grown in vertical farming is primarily based on artificial lights such as light-emitting diodes (LEDs) sources instead of natural sunlight (Figure 2). Therefore, light conditions, such as light intensity and spectral quality, greatly influence plant growth and development by improving crop nutritive value along with the regulation of the proton motive force (Pocock, 2015). LEDs constitute the most promising artificial lighting source within controlled environmental horticulture as supplementary or a single source of illumination due to their stable output, durability, applicability in specific light spectrum, manageability, and cost efficiency (Avgoustaki & Xydis, 2020; Shamshiri et al., 2018; Zhang et al., 2020). LED light has high photon-use efficiency because it emits specifically targeted wavelengths with a narrow-waveband monochromic light (Lu & Grundy, 2017). Based on LEDs’ characteristics, various attempts have been made to understand the effect of different light compositions, intensities and photoperiods on crops grown in indoor vertical farming including far-red, red, green, blue and UV light respectively and in the combination of different light spectrums (Wong et al., 2020). For instance, moderate LED light application during their production stage could significantly enhance plant growth and metabolism by enhancing the nutritional level and reducing nitrate content in food crops (Bian et al., 2018; Table 1).

Figure 2. Vertical farming with LED lights technology. (a) LED lights for the shipping container farming in Nottingham Trent University. The effect of different light quality and intensity on plant quality has been investigated. (b) Data interpretation with optimal LED light systems in growing-underground farm (photo provided by Zero Carbon Food Ltd/Growing-Underground).

Table 1. The state-of-the-art technologies in vertical farming/urban farming (2017–2022).

Materials	Cultivation method	Technology	Key findings and performances	References
Spinach	Aeroponic	IoT for online and automated monitoring	Based on the real-time and online system, IoT system allows monitoring following key parameters including relative humidity, root temperature and light intensity. Within the system, it was possible to control for ideal temperature for spinach in an aeroponic system.	Jamhari et al. (2020)
Lettuce (Lactuca sativa)	Aquaponic	Centre for hydroponic and aquaponics technology (CHAT)	Centre for hydroponic and aquaponics technology (CHAT) are based on the data which are evaluated and validated by the automated monitoring and controlling system. The real-time data was collected regarding pH and temperature of nutrient solution. Automated pH controller enables to maintain the optimal condition for hydroponic system indicating well growth of lettuce.	Lizbeth and Rico (2019)
Plants	Hydroponic	IoT for smart irrigation system with real-time hardware	Smart irrigation system based on the real-time analysis, so called ThinkSpeak IoT platform, monitor and control the follows parameters including the rate of water flow, temperature and humidity. Furthermore, compared to conventional irrigation system, smart irrigation system enhances crop yield with high efficiency.	Lakshmiprabha and Govindaraju (2019)
Plants	Hydroponic	Wireless sensor and actuator networks (WSAN)	The wireless sensor and actuator networks (WSAN) were utilised to control the environmental condition of two hydroponic chambers. The system obtained heterogeneous data from hydroponic source and send the data to monitoring centre.	Stefan et al. (2019)
Plants	Hydroponic	Smart hardware	Smart system allows to control humidification with optimal temperature for plant and to monitor water temperature, pH level and nutrient level in water tank by utilising micro-controller and further sensor.	Supriyanto and Fathurrahmanim (2019)
Pakcoy (Brassica rapa)	Aquaponic	IoT system within the smartphone mobile	Owing to automagical control and monitor system, the following parameters were successfully evaluated within small error results which are temperature, water level, pH, ammonia gas within the sensor. The accurate IoT system and smartphone application allows produce better quality of crops.	Zaini et al. (2018)
Mustard greens (Brassica juncea)	Hydroponic	IoT to monitor and control	Utilising device called Raspberry Pi allows to monitor and to control the environmental parameters including pH, temperature, humidity and circulation of water effectively based on the real time data. The plant grown with IoT controlling and monitoring system shows better growth performance.	Nurhasan et al. (2018)
Lettuce (Lactuca sativa)	Hydroponic	Smart farming system	The overall quality of lettuce grown in smart system present better growth performance than normal growing system. The smart system analyses optimal practices for hydroponic lettuce within effective system for temperature control and automatic preparation of nutrient solution.	Changmai et al. (2018)
Vegetable crops	Hydroponic	IoT application for smart farming	Smart farming system is combined with the remote sensing system and data which are collected from water module and environment testing towards decision tree algorithm. A decision support system will produce for growers to optimal management of plants with remote monitoring system.	Thakare et al. (2018)
Stevia (Stevia rebaudiana)	Hydroponic	Prototype using Arduino IDE	It is greatly critical for growing Stevia to consider the relative humidity. Within the integrated monitoring and controlling system, Stevia is grown. In order to carry reliable measurements, further developed system are required within the various adjustments.	Ossa et al. (2018)
Vegetable crops	Hydroponic	NI LabVIEW and AVR microcontroller	Combined system with NI Lab VIEW and AVR microcontroller system is an automated based on the real time data. The smart system suggests very successful implementation indicating great stability and control actions which is a user-friendly system without human intervention neither monitoring.	Adhau et al. (2018)

Automation and precision urban farming

One of the major concerns in vertical farming is variability in food crops which is possibly caused by unequal growing conditions such as temperature or light (Beacham et al., 2019). However, controlled environment growing systems in vertical farming allows monitoring and controlling of the growing conditions precisely by real-time based sensors. For instance, big data and the Internet of Things (IoT) technology can lead to advanced knowledge and future smart ‘intelligent’crop production with the application of software or firmware (e.g. LED lights and nutrient recipes). Big data analytics in agricultural databases will be extremely useful for precision farming development. To achieve optimal crop growth, resource use efficiency (e.g. energy, water, nutrients), reduce costs and ultimately move towards growing crops with higher quality, further continuous monitoring and control systems are required based on the measurement of plant physiological traits and microenvironmental conditions that creates precise and timely proprietary big data, generated against multiple inputs/ingredients from the Vertical Farming growing environment. Primary parameters include light, nutrient solution, plant phenotyping and environment (e.g. temperature, relative humidity, CO₂ concentration in the air and oxygenation level of the water) (Stefan et al., 2019). The data can be transmitted through a wireless solution, and then be presented in a cloud-hosted monitoring and control platform that offers real-time data, remote management of robotics (to ensure optimum conditions are maintained), an end-user dashboard and alerts. All data can be stored in the wireless sensor and actuator networks, to be utilised by data scientists/vertical farming specialists to develop an algorithm including deep learning and AI approaches to calculate optimum growing recipes for nutritionally dense crops and ensure optimum energy/resource efficiency (Kozai et al., 2018; Mohmed et al., 2022).

An automated system would be an excellent alternative for indoor vertical farming in combination with real-time data from an IoT system allowing the enhancement of cost-efficacy monitoring and control systems and the reduction of human interaction, along with smartphone applications (Adhau et al., 2018). Additionally, smart growing systems with automation enable growers to customise the environmental conditions for functional foods. Automated urban farming constitutes one of the most promising techniques that offset the high initial installation costs of vertical farming by utilising low-cost sensors and reducing extra labour inputs.

Discussion - overall opportunities and challenges

Vertical farming takes traditional farming to new levels. Unlike conventional soil-based farming and horizontal crop growth on a single level, vertical farming implements soilless cultivation into vertical growth on multiple levels in a protected indoor environment (e.g. glasshouse, buildings). This allows growers to provide fresh, safe and nutritious food year-round whilst promoting crop yield and profitability without interference from soil-borne pathogens (Treftz & Omaye, 2016). Vertical farming and urban farming significantly increase plant productivity per unit of area compared to horizontal hydroponic culture (Kalantari et al., 2018; Touliatos et al., 2016). Automatic monitoring and control systems allow growers to plan flexible growing schedules and nurture crops by securing optimal environmental conditions and nutrient solutions based on precise calculations.

Furthermore, resource use can be highly efficient in terms of water, CO₂ and fertiliser with minimum adverse environmental pollution (Kozai et al., 2015). Vertical farming permits enhanced efficiency in the use of resources, including land, water, light energy, electrical energy and inorganic fertiliser. Agriculture currently uses 70% of all water consumed globally, vertical farming can help prevent water scarcity (closed-loop water systems). A reduction in unsustainable global demand for land and water for arable use could attract investment for industrial-scale farms to become commercially viable (Kalantari et al., 2018; Kozai et al., 2018).

Although vertical farming and urban agriculture are promising sustainable mitigation for food security, several challenges remain. First, the high initial expense of infrastructure is one of the major challenges for vertical farming. To offset the high costs, it is necessary for modern vertical farming to enhance resource efficiency to improve crop yield and quality along with the installation of an intelligent automated controlling system to enhance labour and energy efficiency (Kalantari et al., 2018). Also, the complexity of the system requires teamwork and optimally designed tasks and processes. Secondly, there is controversy regarding energy-intensive use, including light, temperature, and humidity that needs to be controlled (Kozai et al., 2015). Kozai et al. (2015) suggested several ways to reduce electricity costs in vertical farming by; i) a new cheap and energy-efficient LED lighting usage; ii) installing a well-designed light system to match spectral characteristics with plant type and physiology for greatly increased yield; and iii) using renewable energy (e.g. solar energy wind-based or geothermal based energy), waste heat, which would reduce energy expenses and increase energy use efficiency (Avgoustaki & Xydis 2020; Kozai et al., 2015).

Thirdly, there is a limited range of crops that is suitable for this business model (Nin et al., 2018). Technically vertical farming allows the cultivation of all kinds of vegetables, including leafy greens, herbs, medicinal plants, fruiting crops, root vegetables, and grains. At present, the variety of crops grown commercially in vertical farming is typically limited to leafy vegetables and microgreens. However, in addition to the crops mentioned above, vertical farming can also grow functional foods from medicinal plants and micronutrient fortification in food crops that have high value and profit. For instance, previous studies found that several cereal crops and tuber crops could grow well in vertical cultivation with controlled environmental conditions including the strawberry (Wortman et al., 2016) potato (Čížek & Komárková, 2022), bean (Stoochnoff et al., 2022), and wheat (Asseng et al., 2020). Further advanced technologies are needed to facilitate the growing various crops vertically.

Conclusions

There are significant challenges that hinder the prevalence of vertical farming including high initial expenses, shortage of expertise, and requirement for a controlled growing system. However, vertical farming is rapidly becoming more appealing to the world due to its ability to deliver reliable and sustainable food. It can reduce water consumption and land degradation, lower pesticide/fertiliser use, and shorten the food supply chain. Therefore, we suggest that more research and collaboration are important to bring together the current technological practices to increase sustainability. Furthermore, it is expected to optimise product quality in vertical farming and urban agriculture for new capabilities in the agricultural and horticultural industries.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials.