The study, published in Food and Energy Security, is believed to be the first to fully account for soil emissions from field farming while comparing them to crops grown in a commercial vertical farm in the UK.
Taking a cradle-to-store view of lettuce production, researchers analysed two UK farms – one on mineral soil and one on peat-based soil – and a farm in Spain, which together supply most of the UK’s lettuce. They then compared these with the vertical farm.
Results showed that vertical farms can deliver more than 20 times the yield of field farms – around 97 kilograms per square metre compared with just 3.3 kilograms. Water use is also around eight times lower compared to Spanish land farms, where irrigation demands are high (0.9 m³/kg lettuce in vertical farms compared with up to 7.3 m³/kg in Spain).
However, the greenhouse gas emissions remain higher with vertical farming. Even when powered by renewable electricity, vertically farmed lettuce produced about 0.93 kilograms of greenhouse gases for every kilogram grown, compared with 0.57 kilograms for UK field farms.
Higher carbon cost
Michael Gargaro, Postgraduate Researcher at the University of Surrey’s Centre for Environment and Sustainability and lead author of the study, said: “Vertical farming has the potential to transform food security in the UK, particularly as climate change and seasonal drought place growing pressure on traditional agriculture.
Our research shows that while the technology can bring far higher yields and reduce water use, it currently comes with a higher carbon cost. “The challenge now is to make vertical farming more energy-efficient and better integrated with renewable systems, so that it can become a truly sustainable solution.”
High energy demands
Much of the carbon impact was linked to the high energy demands of vertical systems and jute fibre plugs – fibrous blocks made from jute stems that are used to support and grow the plants instead of soil. Researchers found that switching to alternative materials, such as coconut coir, could cut the land footprint of vertical farms by more than 95 per cent – underscoring clear opportunities to reduce their environmental cost.
Dr Zoe M Harris, Director of the University of Surrey’s Centre for Environment and Sustainability, Co-Director of the Institute for Sustainability and co-author of the study, said: “With around 95 per cent of lettuce imported from Spain during the winter months, advances in novel vertical farming technology have made it possible to secure a year-round supply of fresh produce while freeing up land for restoration, such as peatland and woodland. But to viably compete with field farming, vertical farms must cut their energy use and rethink the materials they rely on.”
Innovations in energy and materials needed
The research highlights that while vertical farming is not yet the most sustainable option for lettuce production, innovations in energy and materials could make it a crucial part of future food security in the UK, particularly as climate change and water scarcity threaten traditional growing regions like Spain.
The study was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the Engineering and Physical Sciences Research Council (EPSRC).
The full paper can be found at: https://onlinelibrary.wiley.com/doi/epdf/10.1002/fes3.70117
