Humanity continues its rapid advance towards 3D high-rise living (United Nations 2018), while continuing to rely on a 2D landscape of conventional agriculture. In this context, vertical farming has grown in importance. Hydroponics dominates, but plenty of solid research indicates that the role of soil is overlooked in vertical farming.
In general, soil-based agriculture offers numerous benefits, including better nutrient retention and a versatility that enables the growth of an unrivalled variety of crops when compared to any other growth medium. Healthy soil also has the potential to store up to 1.5 gigatons of carbon per year, equivalent to the annual emissions of the global transportation sector (Lal, 2018, 2020). Soil sequestration can help mitigate climate change effects, and soil-based vertical farming could play a crucial role in these efforts.
However, water usage is a concern in soil-based agriculture, particularly in areas with limited water resources. Hydroponics is typically seen as being much more water-efficient. Few peopel realize, though, that olla irrigation—an ancient soil-based irrigation method employing unglazed clay pots filled with water—can reduce water usage by up to 70% compared to conventional irrigation methods (Mollison, 1991). It remains the most water-efficient soil irrigation method to this day, far surpassing drip irrigation, for example.
In other words, olla irrigation carries the water-efficiency of hydroponics, without the waste associated with constant connectivity and the production and transportation of nutrient solutions. In fact, ollas are so water efficient that they are directly comparable to hydroponics.
Studies routinely find that soil-grown plants have better taste and higher nutritional content than hydroponic or aeroponic counterparts (Lester and Eischen 1993; Giuffrida, F., Leonardi, C., & Rapisarda, P. 2003; Dorais, M., Ehret, D. L., & Papadopoulos, A. P. 2008; Treftz and Omaye 2015). Soil-grown plants exhibit a more diverse and robust microbial community, which plays a crucial role in enhancing plant growth, health, and resilience against pests and diseases (Mendes et al., 2013; Trivedi et al., 2020).
The complex interactions between plants and their associated microorganisms in the soil contribute to improved nutrient uptake, making soil-based systems a valuable component of sustainable agriculture (Bender et al., 2016; Williams & Marco, 2014).). Soil has the clear advantage of fostering a diverse and healthy microbiome that can improve plant health and resilience to diseases.
These complex microbial interactions can help plants access essential nutrients, strengthen their immune systems, and even protect them from harmful pathogens (Bender et al., 2016). Furthermore, soil-based agriculture promotes the conservation of essential soil biodiversity, which is crucial for maintaining long-term soil fertility and supporting sustainable agriculture (Barrios, 2007).
By contrast, in hydroponic systems, the circulation of nutrient-rich water can create favorable conditions for the growth and spread of waterborne pathogens, leading to rapid plant disease outbreaks (Savidov & Brooks, 2004). This leads to a need for constant connectivity and concomitant energy consumption in a non-stop struggle to optimise all variables to mitigate these risks.
Speaking of waste, even hydroponic or non-hydroponic food marketed as "local produce" generates emissions associated with, for example, packaging, or actually getting the produce into consumers hands, and then from their hands to their homes. Vertical farming should be placing a greater emphasis on consumer-friendly solutions to accelerate our transition towards genuinely local food production, straight from consumers' homes.
On top of this, the absence of a diverse microbial community in hydroponic systems can make plants more vulnerable to opportunistic pathogens (Berg, 2009). Soil-based systems with olla irrigation promote a healthier, more diverse microbial community that can help suppress plant pathogens and reduce disease risk (Compant et al., 2010).
Furthermore, the slow release of water from ollas minimizes standing water and damp conditions, which can deter the growth of harmful microorganisms and reduce the risk of human diseases associated with contaminated water (Stikkelman & Bainbridge, 2010). While hydroponics systems might work in a high-tech lab environment, this suggests that they might be less well-suited for the home.
Unsurprisingly, over the course of evolution, the soil-based microbes associated with traditional agricultural methods have entered into a symbiotic relationship with humans, affecting even our mood and psychology, as discussed in our blog post, here. The list of benefits of soil interaction and soil-based crops goes on, which is also unsurprising. After all, we do call this place "the Earth".
By utilizing soil-based farming methods in vertical farming, we can preserve valuable soil ecosystems and promote healthier, more resilient plant growth. Garden Stack combines soil and olla irrigation in its unique vertical farming system, providing the benefits of soil-based agriculture while reducing water usage and enhancing plant growth, matching or surpassing the benefits of hydroponic alternatives. This approach suggests that vertical farming may be neglecting soil-based solutions, which doubtless have a role to play in the future of vertical farming and the construction of sustainable and environmentally-friendly urban agricultural systems.
Sources:
Barrios, E. (2007). Soil biota, ecosystem services, and land productivity. Ecological Economics, 64(2), 269-285.
Bender, S. F., Wagg, C., & van der Heijden, M. G. (2016). An underground revolution: biodiversity and soil ecological engineering for agricultural sustainability. Trends in Ecology & Evolution, 31(6), 440-452.
Berg, G. (2009). Plant-microbe interactions promoting plant growth and health: perspectives for controlled use of microorganisms in agriculture. Applied Microbiology and Biotechnology, 84(1), 11-18.
Compant, S., Clément, C., & Sessitsch, A. (2010). Plant growth-promoting bacteria in the rhizo- and endosphere of plants: Their role, colonization, mechanisms involved and prospects for utilization. Soil Biology and Biochemistry, 42(5), 669-678.
Dorais, M., Ehret, D. L., & Papadopoulos, A. P. (2008). Tomato (Solanum lycopersicum) health components: from the seed to the consumer. Phytochemistry Reviews, 7(2), 231-250.
Giuffrida, F., Leonardi, C., & Rapisarda, P. (2003). Influence of different soilless growing systems and media on yield and quality of greenhouse tomato. Journal of Food, Agriculture & Environment, 1(2), 76-79.
Lal, R. (2018). Digging deeper: A holistic perspective of factors affecting soil organic carbon sequestration in agroecosystems. Global Change Biology, 24(8), 3285-3301. https://doi.org/10.1111/gcb.14054
Lal, Rattan. "Home gardening and urban agriculture for advancing food and nutritional security in response to the COVID-19 pandemic." Food Security 12, no. 4 (2020): 871-876.
Mollison, Bill. "The Use of Ollas in Irrigation." The Permaculture Activist, no. 22, 1991.
Mendes, R., Garbeva, P., & Raaijmakers, J.M. (2013). The rhizosphere microbiome: significance of plant beneficial, plant pathogenic, and human pathogenic microorganisms. FEMS Microbiology Reviews, 37(5), 634-663.
Lester, G. E., & Eischen, F. A. (1993). Beta-carotene content of postharvest orange-fleshed muskmelon fruit: Effect of cultivar, growing location, and fruit size. Journal of the American Society for Horticultural Science, 118(1), 129-133.
Savidov, N., & Brooks, A. (2004). Evaluation and development of aquaponics production and product market capabilities in Alberta. Retrieved from https://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/sag6299
Stikkelman, R., & Bainbridge, D.A. (2010). A field study of the feasibility of clay pot irrigation in San Diego County. Journal of Arid Environments, 74(11), 1477-1483.
Treftz, C., & Omaye, S. T. (2015). Nutrient analysis of soil and soilless strawberries and raspberries grown in a greenhouse. Food and Nutrition Sciences, 6(11), 805-815.
Trivedi, P., Leach, J.E., Tringe, S.G., Sa, T., & Singh, B.K. (2020). Plant–microbiome interactions: from community assembly to plant health. Nature Reviews Microbiology, 18(11), 607-621.
United Nations, Department of Economic and Social Affairs, Population Division. (2018). World Urbanization Prospects: The 2018 Revision. Retrieved from https://population.un.org/wup/Publications/Files/WUP2018-Report.pdf
Williams, T. R., & Marco, M. L. (2014). Phyllosphere microbiota composition and microbial community transplantation on lettuce plants grown indoors. mBio, 5(4), e01564-14.
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