Urban crops can have higher yields than conventional farming

A vegetable display © Roots in the City Community Garden, Liverpool

As urban populations boom, urban agriculture is increasingly looked to as a local food source and a way to help combat inequitable food access and food deserts. But little is known about how productive urban agriculture is compared to conventional, rural farming. A new study led by Lancaster University researchers finds urban gardeners and hydroponics can meet and sometimes exceed the yields of rural farms.

“Urban food growing is often dismissed as something that cannot meaningfully contribute to food security”, said Professor Jess Davies, project lead for the Rurban Revolution project that developed this study. “In this work we set out to examine the global evidence base and gather the hard evidence on whether towns and cities can provide good food growing environments?”

The new paper compiles studies on urban agriculture from 53 countries to find out which crops grow well in cities, what growing methods are most effective, and which spaces can be utilised for growing. The researchers find that urban yields for some crops, like cucumbers, tubers and lettuces, are two to four times higher than conventional farming. Many other urban crops studied are produced at similar or higher rates than in rural settings. Cost efficiency remains an open but important question.

Most studies on urban agriculture have focused on green spaces, such as private and community gardens, parks and field growing operations. This paper includes ‘gray’ spaces — places in cities that are already built but could be used for growing, such as rooftops and building facades. In both green and gray spaces, the study examines a suite of crops grown in soils versus hydroponics, horizontal versus vertical farming, and natural versus controlled conditions.

“Surprisingly, there were few differences between overall yields in indoor spaces and outdoor green spaces, but there were clear differences in the suitability of crop types to different gray spaces,” Dr Florian Payen, lead author and researcher from Lancaster Environment Centre says. Certain crops like lettuces, kale and broccoli are more naturally suited to be grown vertically in indoor spaces than others. “You can’t exactly stack up apple trees in a five or ten-layer high growth chamber,” he says, “though we did find one study that managed to grow wheat stacked up like that.”

Other crops, like watery vegetables (e.g., tomatoes) and leafy greens, performed well in hydroponic environments. And crops grown in fully controlled environments can be grown throughout the year, allowing harvests to happen more times per year than in open-air environments, which leads to higher annual yields. But scientists will need to keep studying these systems to plan cost-effective agriculture solutions.

Current estimates suggest that between 5% to 10% of legumes, vegetables and tubers are grown in urban settings, and between 15% to 20% of global food is produced in cities. But getting a handle on just how much food a city could produce for itself is difficult without yield information like the data presented in the study. Dr Payen and his collaborators are part of Rurban Revolution, an interdisciplinary team building evidence and understanding of the value of urban growing for food security, health and the environment.

“”This study is an important piece of the puzzle – our past work has shown that the UK has a lot of urban greenspace that could be put to use in substantially shoring up our precarious fresh fruit and veg supplies,” said Professor Davies. “Florian’s work has now shown that we could produce even more food than previously anticipated from these overlooked spaces.”

“Put together with our other work on the health and ecosystem benefits, the evidence is building for considering food growing in community gardens, urban farms, rooftops, indoor environments, and back gardens as a serious national opportunity for creating a healthier, sustainable, more resilient food supplies, communities and places.”

DOI: 10.1029/2022EF002748

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