Jan 17, 2020
Urban Greenhouses and the future of food: A 3 part blog series inspired by this book.
Written By: Michele Butturini
The climate crisis is happening (as for some time already), and agriculture is a key protagonist. As elegantly explained by Nazim Gruda, professor at the Department of Horticultural Science of Bonn University:
“Agriculture/horticulture and climate change have a dual interaction. On the one hand, the environment is affected by activities associated with agricultural food production, which contributes to climate change; on the other, the impacts arising from such activities backfire by changing the environmental conditions, thus affecting agriculture and horticulture.”
Vertical farming is often presented as a revolutionary agricultural system of manifold qualities. It sometimes happens to hear stories of vertical farming vaguely reminiscent of the mythical land of Cockaigne – where no effort was needed to get food since it was falling from the sky (Figure 1).
Will vertical farming break the curse, releasing agriculture from its unsustainable environmental burden?
Figure 1. The Land of Cockaigne - Pieter Bruegel the Elder (1567)
To be sustainable, vertical farming has to prove itself capable of minimizing the emission of green-house gases, such as carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4), per kg of food produced. However, a sustainable food system is more than just low emissions of green-house gases. As reported by Tessa Naus, the HLPE definition of a sustainable food system is: “a food system that delivers food security and nutrition for all in such a way that the economic, social and environmental bases to generate food security and nutrition for future generations are not compromised”. Therefore, the challenge is far more complex than merely reducing green-house gases. In an interview from the book “Urban Greenhouses and the future of food”, Leo Marcelis, head of Horticulture and Product Physiology Chair Group at Wageningen University, suggests that vertical farming can address some of the urgent challenges posed by the climate crisis,“there’s the problem of growing enough fresh, high quality, sustainable food and making it available to the rapidly growing urban populations in our rapidly expanding cities. To answer this, we need ever-higher production rates, and our production has to be highly controlled. […] They (n.d.r. vertical farms) don’t need much space and are indoors, they are not dependent on solar lighting, they’re independent of outdoor conditions, and can produce 365 day a year.”
Meeting the growing demand of fresh produce from the city, is an essential challenge for the sustainable food system we are looking for. As observed by Nona Yehia, CEO at Vertical Harvest “by 2050, 80% of the world’s population will live in cities”. According to Leo Marcelis, vertical farms “can be placed in or near-by urban areas anywhere in the world. [..] you can pick the produce when needed and thereby improve shelf-life: at this moment many vegetables are simply thrown away because they have too short shelf-life”. Indeed, even if just a fraction of this food loss along the supply chain is due to its distribution, ultra-short supply chains could significantly reduce the global fruits and vegetables loss, currently at 42% of kcal wasted. Furthermore, there is evidence that indoor grown leafy vegetables can have a longer shelf life thanks to a higher antioxidant level. However, even if ultra-short supply chains have very little food-miles (Figure 2), they aren’t always necessarily the most sustainable choice. As reported by Nazim Gruda: “Tomatoes imported from Spain can have two to four times lower global warming potential than those produced locally under intense heating in Austria and in the UK”. Being part of a sustainable food systems also implies making efficient use of water and land, and that’s what vertical farming does better than both greenhouse and conventional agriculture (See Figure 2). Thanks to the optimized growing condition and the recirculation of the nutrient solution, not just water, but also fertilizers have the highest use efficiency currently possible for an agricultural system. More in general, the overall use of agrochemicals could be minimized, since pesticides and herbicides are theoretically unnecessary.
Figure 2. (Photo Credit: PlantLab, source “Is vertical farming really sustainable?”)
Yet, from a sustainability perspective, vertical farming has still some significant flaws. Leo Marcelis points out that “Vertical farms do however need large amounts of energy, and this is an area we are currently working on; they will always need electricity in the future. So, energy use is a current pitfall as it mainly comes from fossil fuels”. On a global scale, about 60% of the electric energy is still generated by the burning of fossil fuels, that is a process that generate a huge amount of greenhouse gasses. The intense use of electricity mainly depends on the fact that vertical farms are cultivation systems that use artificial light to grow plants. Thanks to the technological advancement, the photosynthetic efficacy of horticultural LEDs has been rapidly increasing in the last few years and further improvement is to be expected in the future (Figure 3). On the long term, however, LED photosynthetic efficacy will stabilize around 4.7 μmol/J due to intrinsic technological limitations. Nonetheless, addressing the overall energy efficiency of a vertical farm is not just about improving the LED efficacy. A lot will be achieved by developing better cooling and dehumidification technology, minimizing energy losses and breeding new crop varieties specific for vertical farming. Leo Marcelis is convinced: “in the near future, these current pitfalls will fade away – less energy will be needed”.
Figure 3. Progress of photosynthetic efficacy of LED lighting for horticulture over time. Photosynthetic efficacy is the ratio between the “photosynthetic photon flux” and the electrical source power used to create that photosynthetic photon flux (from LED lighting efficacy: Status and directions).
However, on the sustainability front, the intense use of electricity is not the only flaw of vertical farming. First of all, the environmental impact of building a vertical farm is still uninvestigated, nonetheless, it is known that the manufacturing of the construction parts of greenhouses, such as glass, steel, and concrete have high CO2 emissions (should we start thinking about vertical farms made of bamboo?). Moreover, peat and rockwool, which are very commonly used as substrates for hydroponic cultivation, have a high carbon footprint: peat is harvested from peatlands, which are extremely important long-term stores of organic carbon, while the manufacturing of rockwool is energy-intensive. Last but not least, intense and year-round hydroponic production requires fertilization. Even if the fertilizer use efficiency in a vertical farm is extremely high, the use of synthetic nitrogen fertilizers has a significant environmental impact because of the emissions of N2O, NH3, NOx during their manufacturing and application process. To address this issue, a potential solution could be to extract the nutrients that plants need from composted biomass. In Sweden, for example, Bonbio and Ikea are testing a container farm system that grows lettuce using a nutrient solution produced from organic waste
Figure 4. (Photo Credit: IKEA, source “Ikea now grows lettuce in shipping containers at its stores”).
The transition towards sustainable agriculture is urgent. All in all, vertical farming is a good candidate for the creation of a sustainable food system. However, it is not a one-size-fits-all solution. To use the words of Tessa Naus: “ The best way of thinking of vertical farming, is probably as a technology which would be complementary to traditional farming techniques. The sustainable food system envisioned by Tessa Naus could be defined as “Multi-agriculturalism”: a food system that achieves sustainability by using, depending on specific local characteristics, vertical farming, organic agriculture, greenhouse horticulture and the rest of the long tail of sustainable agriculture. The technology behind vertical farming is not yet definitive and a lot can still be gained on the sustainability front: by reducing dependency on mineral fertilizers, by making substrates and construction materials more sustainable and by increasing the overall energy efficiency. To do so more initiative as the one of Bonbio and Ikea must come. We have to transform the way humans interact with planet Earth: let us not underestimate what is at stake.
Acknowledgement:
I thank Sander van Delden (Wageningen University and Research), Mehdi Bisbis (Leibniz Institute) and Luuk Graamans (Wageningen University and Research) for providing very useful information.
Short Bio of the Author
Researcher at the department of Horticulture and Product Physiology, Wageningen University (NL). Passionate about urban farming, vertical farming and controlled environment agriculture.