Just a few miles north of Columbia University in Yonkers, the Science Barge floats on the Hudson River, demonstrating a fully functioning system of renewable energy based sustainable food production. The barge cum 1300-square-foot greenhouse is a model urban farm powered by solar, wind, and biofuel, whose crops are irrigated by recycled rainwater and river water. And despite its river setting, the Science Barge is, in fact, a prototype for rooftop gardening.
Traditional agriculture relies heavily on fossil fuel based fertilizers and is responsible for about 10 to 12% of estimated global GHG emissions each year. With the continuing erosion of one third of the world’s cropland, a looming water crisis, soaring food demand, and half the global population now living in cities, there is an urgent need today to develop and implement sustainable ways of growing food in urban settings.
The Science Barge is capable of growing as much as one acre of land—and has produced 35 tons of tomatoes in just 3% of the space that would be needed for traditional farming. Last week, the first harvest of the season yielded 50 lbs of produce— every two weeks, the harvest is donated to a local food pantry.
Promoting high-yield, safe, and sustainable urban food production, the Science Barge educates students of all ages about how it is done. It was constructed and originally operated by New York Sun Works. In 2008, the Barge was acquired by Groundwork Hudson Valley, the local arm of Groundwork USA that promotes environmental, economic and social well-being through working with communities. Students from New York, New Jersey, and Connecticut visit the Science Barge, and other organizations and groups are welcome as well. On weekends, it is open to the public.
The centerpiece of the Science Barge is its recirculating hydroponic system called the Nutrient Film Technique (NFT). Plants are grown in a substrate (growing medium), placed in long plastic piping with holes cut into it, and nourished with a small stream of water that carries all the nutrients plants need directly to their roots. As a result, the plants do not need to expend energy creating the kind of root systems they would need in soil, and can grow more quickly in less space.
Rainwater collected in 1200-gallon drums, and river water desalinated (since the Hudson is a tidal estuary where saltwater from the sea mixes with freshwater) by a small reverse osmosis system is used to irrigate the plants, and all water is recycled. The excess water is saved and stored in a collecting bin where it is tested daily for nutrient content and pH before being reused. NFT uses only 10% of the water that growing the crops in soil would require.
Seedlings for leafy vegetables such as lettuce, arugula, chard, and herbs are started in chunks of a substrate called rockwool, made from rocks and sand, which holds large quantities of water. After two weeks, the plants are moved to the nursery rows of the NFT, and then after two more weeks, to the finishing rows where they grow to maturity for another two weeks. They are constantly monitored for insects, which are dealt with through integrated pest management involving prevention, observation and intervention. Gwen Hill, greenhouse manager and director of education, explained that when pests are discovered, they are identified, and then appropriate predatory insects are brought in to feed on them.
Fruit-bearing vine crops such as tomatoes, cucumbers, melons, and peas are grown vertically in Dutch or Bato Buckets made of plastic and containing small reservoirs of water. They also use the NFT recirculating hydroponic system. However, vine crops are allowed to climb up cords and encouraged to grow both up and around, so that, for example, tomatoes can grow to be 25 to 30 feet tall!
The Barge’s experimental aquaponics system combines fish culture with hydroponics. Fish live in a tank, are fed worms and compost tea (the drainage from the composters), and their wastewater is piped up into a growing container to nourish the plants’ roots. Gwen explained that the system is not quite working yet because they don’t have enough fish to provide the nutrients, or the beneficial bacteria needed to break down the waste.
On deck, a section is set aside for 10 species of wetlands plants that demonstrate how wetlands naturally purify water. Wastewater from the NFT system and other dirty water is drained into the wetlands area, and once cleansed, is recycled. In addition, two different style composters inhabited by communities of red wiggler worms turn food and crop waste into rich fertilizer.
The whole operation runs on renewable energy with zero carbon emissions. Two photovoltaic solar arrays, incorporating a passive tracking system, produce 2.5 kWh of electricity. A gas called R134A in the frame reacts when the sun heats it, expanding and moving to the other side of the array; the weight change causes the photovoltaic array to tilt to track the heat of the sun, enabling it to produce 20% more electricity than a fixed system would. In addition, the Barge’s five small wind turbines produce 2kWH that power the hydroponic systems. A furnace that runs on vegetable oil heats the greenhouse in winter.
Urban farms akin to the Science Barge are already popping up in New York and elsewhere. Gotham Greens, a 15,000-square-foot greenhouse on a Brooklyn rooftop that will produce over 80 tons of produce yearly for restaurants and retail outlets, is scheduled to begin harvesting in June. BrightFarms, a company that designs, finances, develops and manages hydroponic rooftop greenhouses, is designing a demo greenhouse for Whole Foods in Millburn, NJ, a greenhouse for the Cypress Hills Community School in Brooklyn, and a 10,000-square-foot rooftop farm for an affordable housing complex in the South Bronx. And San Francisco based Sky Vegetables is planning a one-acre rooftop greenhouse on top of an old shoe factory in Brockton, Massachusetts.
Of course, a substantial initial investment is required to construct a hydroponic greenhouse, and it’s too soon to tell if rooftop farming will prove economically competitive with traditional farming. But if you consider their ecological benefits, urban farms— that cultivate unused rooftops and harvest safe fresh produce, while eliminating fertilizers, pesticides, and food miles, cutting carbon emissions, and saving water—just might be the answer to some of our global problems.