As the world's population continues to grow and urbanise, many sustainable development advocates have argued that more holistic urban planning must provide for food production taking place in the towns and cities where people live and eat.

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According to the UN, 80 percent of the world's population will live in urban areas by 2050. The planet is expected to be home to 9 billion people by that time, and finding ways to provide enough food whilst avoiding environmental collapse is proving to be one of the most challenging conundrums currently facing humanity.

Exponents of urban agriculture believe that bringing food production into towns can protect the environment by reducing the land needed for farming, growing on top of buildings and in indoor 'vertical farms', whilst providing more affordable healthy food with a reduced ecological footprint, made possible through cutting transport costs and, in many cases, direct selling.  

In Chicago, pioneers of urban agriculture have taken the challenge of producing food in cities to heart and broken new ground in the 'field'; in March, the world's largest vertical farm opened in the city's suburbs, adding to a diverse range of existing urban growing initiatives, now two interdisciplinary experts from the University of Illinois are investigating the benefits and potential drawbacks of urban agriculture, in a bid to bolster urban growing, a sector with clear potential but which remains in its infancy.

The boom in local food culture has given rise to a number of urban growing schemes in and around Chicago, which University of Illinois' Professor Sam Wortman said has proved a boon for some of the city's restaurants and food stores. "You can't find fresher food anywhere, Chefs are literally picking produce the same day they're cooking it in the restaurants," he enthused.

Professor Wortman and colleague Sarah Taylor Lovell have been investigating the city's Urban growing projects. They are both strong advocates of urban agriculture, but recognise that organisers and growers face challenges, which must be understood and addressed if urban gardens and agriculture initiatives are to become widespread and even profitable. The principal obstacles, according to profs Wortman and Taylor Lovell, are soil contaminants, water availability, and changes to climatic and atmospheric conditions.

Sustainable planning experts address urban ag hurdles

As many urban agriculture projects are on reclaimed land, contaminants can make the ground unsuitable for growing; of these, lead is the most prevalent in Chicago. This means that many areas must use raised beds, or make sure crops are not in contact with potentially contaminated ground. Even so, while they do admit to concern over the possibility of plants taking up lead from soils, According to Prof Wortman, research suggests that they actually absorb very little. "Even in roots, there is still a relatively small amount of lead compared to, for example, what we're exposed to from drinking water," he said.

Nevertheless, direct ingestion of soil is a greater concern, as concentrations of lead are much higher in soil itself – as soil adheres to crops after they're harvested, and spreads around when disturbed, sustainable planner Taylor Lovell recommends educating consumers on the importance of washing food well, and covering soils with mulch to minimise risks.

Finding reliable and safe water sources can also prove difficult for urban farmers. Technologies such as drip irrigation that precisely deliver water where and when it's needed can help conserve water, and many of the pioneering vertical farms operate a 'circular system' to reuse water. Profs Wortman and Taylor Lovell said reusing rainwater and grey water can provide additional water, but that these too must be monitored for contaminants, and may require treatment.

Over the course of their research, the pair also discovered that changes in atmospheric and climate conditions in cities may affect crop health in ways that have not previously been considered. Compared to rural areas, cities have higher temperatures and vapour pressure deficits (VPD – a measure of moisture in the air, and how much moisture air can hold before forming clouds or dew droplets); in some areas this could increase plants' susceptibility to disease.

More extreme temperatures during the day and higher night time temperatures can also inhibit photosynthesis in plants and affect yields. Higher VPD can also impact on plants use of water, creating moisture stress and reducing photosynthesis.

Research underway to examine urban ag projects

To better understand the effects of varying climates and atmospheric states on food production, Wortman and his colleagues have launched an investigative project. They are looking at six sites on a gradient from downtown Chicago to 40 miles west of the city. The sites all have the same, ideal soil conditions allowing the researchers to take soil factors out of the equation.

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"We are trying to isolate the effects of the atmosphere," Wortman explained. "We are monitoring concentrations of carbon dioxide, ozone, temperature, humidity, wind, and other factors across all of the sites."

Although the study is still ongoing, the preliminary results are exciting, according to Wortman. They show crop yields are highly variable at the different sites, with some crops growing better closer to the city centre and others producing higher yields in more rural areas. The variability suggests that the effects of atmospheric conditions on crops are important in development.

The pair are seeking to identify crops that grow well in any given urban environment, which would strengthen current urban growing operations and potentially lead to the development of new crops, specifically adapted to urban conditions. However, Wortman is also keen to examine the effects of cities' higher temperatures, and concentrations of ozone and carbon dioxide, which he believes will provide an advanced snapshot of the effects of climate change on food production.

Thanks to the 'natural laboratory' provided by urban food growing, Wortman and colleagues hope they may be able to discover tools to address some impacts of climate change.

"We're looking at it from a very practical perspective of providing recommendations for urban farmers, but it also has an angle of how these different crops respond to altered environments," said the professor. He added that, as well as optimising production in urban areas, more effort is needed to ensure that food grown in cities is available for all citizens, and not those at a socio-economic advantage.