SWITZERLAND IS taking the concept of rooftop food production a step further with a new 'aquaponics' system that could revolutionise urban farming.
With seven billion to feed, human agriculture exerts a tremendous toll on the planet, from water and air pollution to energy use and habitat loss. But with every great challenge comes the possibility of great sustainable solutions. With land at a premium and population rising, could urban farming be one of them?
Rooftop farms provide a new experience by revolutionising the idea of fresh produce. When food is grown directly on the roof, just a few steps away, consumers can see, smell, and taste the difference.
What’s more, rooftop farms enable businesses to monetise vacant real estate assets and reduce their environmental impact. Urban rooftop farms save energy, water and natural resources. They’re also scalable: farming vegetables and fish on rooftops without fossil-fuel-based fertilisers, chemical pesticides or antibiotics can be done as a small home-based system, a large supermarket-based one – and anything in between.
By growing what is needed, near where it’s needed, food miles are also cut. It’s the freshest produce money can buy, and there’s no excuse not to eat in season. The question is: what’s not to like about urban farming and why isn’t there more of it about?
The concept of growing food in cities isn’t new. In the postwar period the allotment offered many city residents a necessary complement to their weekly supplies.
And there’s a growing army of small-scale farmers today. The Swiss Family Gardener Association, for instance, has 25,000 members making use of 640 hectares of land. This might only be 0.2% of the total arable land in Switzerland, but nearly 5% of the vegetable crops are grown in that space.
But with more people comes the need for more buildings. Green space in cities is being hoovered up, with backyards shrinking or disappearing. But that has forced the world’s urban gardeners and farmers to look at the world in a different way. Specifically, they’ve looked up.
Rooftop farms belong to a special category of food production and cannot be compared with the conventional greenhouse plants that we find not far from city centres. Roof farms in urban areas aim to supply local markets and take advantage of the short transport distances.
Freshness and enjoyment are the two trump cards for today’s growing army of urban farmers. Growing salads such as salanova (a modern type of lettuce), tomatoes with different flavours, microgreens and herbs can provide a very good basis for gourmet restaurants.
These are not competition for professional vegetable farms – they are an additional supply stream. And it’s not just carrots
and peas that are sprouting up on rooftops either.
Aquaponics is the combination of aquaculture (fish) and hydroponic cultivation of plants without soil. The technology works as a closed-loop system that reduces consumption of fresh water compared with conventional monocultures; meanwhile, the nutrients excreted by the fish are passed through a biofilter and used as fertiliser.
This marriage of age-old techniques and cutting-edge technology makes the system unmistakably Swiss, and the first 260-square-metre professional pilot plant was completed just over a year ago in the Dreispitz area of Basel.
The farm can produce about 0.8 tonnes of fish and five tonnes of vegetables – small fry in output terms, but it’s a pretty small roof. Replicate it and the numbers become a lot more impressive.
Basel has an estimated 2m square metres of vacant rooftop space and researchers at the Zurich University of Applied Sciences have calculated that if just 5% of that space (100,000 square metres) was used for aquaponic production, 40,000 people could be fed. This means that theoretically the city’s entire population of 170,000 could be fed if just 20% of the vacant roof space was converted into aquaponic farms.
Local restaurants support the idea of more rooftop farming systems and have been busy buying the products – some chefs even helped with harvesting. They have also given the researchers a wish list, including speciality foods that they spend a fortune importing from miles away.
This type of technology doesn’t come cheap either, though. The production costs of a rooftop farm are eight times higher than that of a large greenhouse, not least because of existing building regulations – the fish basins need a load capacity of about one tonne per square metre – and the requirements for heating, ventilation, shading and energy. Scale helps – a rooftop of more than a thousand square metres makes a big difference.
So could UK farmers follow their Swiss counterparts up the stairs to the rooftops? Existing farmers would certainly like to learn more about the possibilities of systems using aquaponics, especially to produce speciality crops that attract high prices from restaurants and premium catering operations.
However, more research is needed, especially into reducing energy use, nutrient use and the best use of space. I’m working very closely with the Urban Farming Company and a farmer in Cupar, Fife, to develop the systems in the UK.
There is much work to be done, but so much potential to produce good food in our cities. Could the waste heat from buildings be used to heat greenhouses, for instance? Or perhaps the carbon dioxide rich air being belched out of buildings could be fed directly to plants?
The options are almost limitless. I’m in no doubt that aquaponics can help bring food security within the next few decades. The beauty is that we’ll be feeding people using land that we are already using to house them and protect them.
Valentini Pappa is a specialist agriculture- environment researcher at Scotland’s Rural College