Vertical farming: a toolbox for securing vegetable yield for the food of the future

Abstract

Agriculture has been a part of much of the history of man and his societies, but the impact of modern agriculture on the environment is undeniable, leading to air and water pollution, soil, water and mineral depletion as well as decreases in biodiversity. By 2022, the agricultural sector alone contributed around one-third of the 54 billion tons of greenhouse gases emitted by humans (Crippa et al., 2023;Ritchie and Roser 2024). Considering such staggering numbers, the agriculture and food sector is called upon to implement urgent and necessary changes (de Carbonnel et al., 2022).To limit the effects of industrial-scale agricultural land use on the global climate, vertical farming (VF) might hold a number of solutions towards more sustainable crop production.VF has its roots in the rudimentary hydroponic systems first developed by the ancient Egyptians (4th century), Chinese (12th century) and Aztec (14th century) civilizations. Vertical farming systems were made possible through the development of modernized greenhouses, artificial lighting and soilless growing techniques. While the term "vertical farming" was coined by geologist Gilbert Ellis Bailey in 1915 (Bomford, 2023), the first truly competitive VF enterprise on the market only emerged in Singapore in 2012.In 2023, the size of the global VF market was estimated at about $7 billion and is expected to grow by another 20 percent by 2030 (Grand View Research, 2017). As the effects of our changing climate are becoming more evident, this growth is mainly attributable to the increasing interest in more sustainable production systems and models. It is therefore no coincidence that in 2023, VF start-ups raised about $50 million, representing a 65 % increase from 2022. In early 2024, the world's largest vertical farm covering about 14,500 cultivable square meters opened in Lydney, Gloucestershire, UK. Despite Europe dominating the VF market in terms of sales and with a share of more than 30 percent, European agricultural policies have shown only modest support in new and more innovative agricultural production systems. Conversely, federal policies in the United States fund the development of indoor agriculture much more generously. However, in both the EU and the US, produce grown in vertical farming systems is not labeled as organic as it does not comply with the definition of organic food due to the complete absence of soil (Kumar et al., 2023).Today almost 60% of the world's population lives in urban and peri-urban areas (Dagar et al., 2023). This number is set to grow to 68%by 2050; not to mention that by the same year the world's population is projected to reach 9 billion (Bahar et al., 2020). The greatest demand for food will therefore come from people living in urbanized areas. Crop production via vertical farming systems could significantly increase in importance as rapid urban population growth will inevitably come up against price and production volatility, seasonality, and poorly functioning supply chains, aspects that will limit, both in physical and economic terms, the availability of fresh vegetables (Pinstrup-Andersen, 2018). Vegetable production via VF would also guarantee greater resilience to catastrophic events that threaten supply chains, including future pandemics, extreme weather events, etc.Open field crop production, too, is more negatively affected by uncertainties and risks directly associated with abiotic and biotic stressors and the effects of climate change compared to vertical farming systems. As the impacts from climate change worsen, the benefits from indoor cultivation may provide higher food security for future generations (Van Delden, 2021). The massive use of pesticides and fertilizers as a tool to ensure food security in open field production is also not sustainable considering the effects on both human health and the environment (Devi et al., 2022). Vegetable production through VF does not require pesticides and herbicides as growing conditions (day and night temperature, humidity, and light quantity and quality) are fully controlled. Water consumption, too, is greatly reduced, with VF producing the same amount of vegetables but using only 5% of the water (Pinstrup-Andersen, 2018). For example, the integration of high-efficiency hydroponic systems allows for the application of only those macro-and micro-nutrients and water strictly necessary for plant growth. This limits water contamination, carbon dioxide emissions and reduces the economic costs associated with fertilizer production and use. The integration of techniques to biofortify vegetables with essential micronutrients beneficial for humans (iodine, selenium, zinc, and iron) would also be possible through the meticulous control of plant nutrition (Avnee et al., 2023).It is further estimated that more than a quarter of the world's population suffers from micronutrient deficiencies, so the ability to produce vegetables at a lower cost is a crucial step towards improving the health of people, particularly those with limited means and access to fresh produce. Building vertical farms in urban centers would also significantly shorten the supply chain, reducing transport-related carbon dioxide emissions and minimize the time between harvest and consumption, ensuring maximum freshness of the product for the consumer.Notwithstanding all the advantages, even the most ardent supporters of VF admit that the enormous use of energy presents a serious obstacle toward the successful implementation of such production systems, particularly in parts of the world where access to reliable energy sources is not guaranteed. It is estimated that VF occupies only 30 of the world's 500,000 hectares of land devoted to protected cultivation (Terazono, 2020). Currently, we cannot yet produce large amounts of energy without impacting the environment, therefore the "energy problem" for VF must not be neglected (Stanghellini & Katzin, 2024). Although renewable energy sources, such as photovoltaic panels can become part of the solution, the environmental and financial costs associated with their production, transportation, installation and disposal are often overlooked. In general, the overall supply of "green" electricity remains insufficient.Another challenge links to the lack of social acceptance toward the implementation of vertical farms. Consumers consider more technological production methods as 'unnatural' and potentially harmful to human health. This misconception is the result of a lack of information about the concepts behind soilless cultivation. It is therefore paramount to improve communication with consumers, clearly explaining the advantages and disadvantages of indoor cultivation (Van Gerrewey et al., 2021).Vertical farms should be understood as facilities that are able to produce horticultural species even and especially there where external environmental conditions are highly controlled (extreme temperatures, polluted soils, unavailable and/or poor quality irrigation water, etc.).Especially in these contexts, growing crops completely untethered from external conditions would prove to be a benefit that would outweigh the associated energy costs.