Urban Agriculture
The urbanization of the planet is drawing agriculture and small farms into city centers in both low-income and industrialized economies. Catering to this trend requires more effective use of space, urban-waste recycling and in some cases sophisticated technology, such as that used in vertical farming.
Urban agriculture is nothing new. Travelers arriving in Babylon at the beginning of the second millennium B.C.E. described the orchards, vegetable gardens and cultivated fields in the suburbs of the immense Mesopotamian city. Overhead there were the “hanging gardens”, one of the Seven Wonders of the Ancient World, producing fruit for the court of Nebuchadnezzar and offerings for the gods.
In more recent times, the industrial revolution brought about the creation of “allotments”, first in England, then in continental Europe. These often carried with them a certain moral aspect, encouraging the working class to maintain rural and family values in the heart of the city with its many temptations.
Today, innovation and research on agriculture in urban environments are being spurred by the global population growth and rapid urbanization expected over the next decades. Ideas range from micro-gardening targeting the most disadvantaged populations in Africa and South America to highly futuristic vertical farming operations in Japan and North America1.
A Reality in Developing Economies
The Food and Agriculture Organization of the United Nations (F.A.O.) defines urban and peri‑urban agriculture (UPA) as the growing of plants and the raising of animals within and around cities2. UPA already provides for the needs of a quarter of the world’s city-dwellers. Further development of UPA is essential given the growing urban population, which has increased at a rate almost twice that of the overall population in only ten years. According to the F.A.O., more than half of all inhabitants of developing economies, or 3.5 billion people, will be concentrated in cities by 2025.
To feed these new residents, it will be necessary to maintain agricultural zones in peri-urban areas to slow down deforestation and reduce energy costs incurred by the cold chain and transportation from producer to consumer regions. The F.A.O. funds programs that encourage disadvantaged urban populations to grow micro-gardens for their own consumption and also as a source of extra income. With the right care, a one-square-meter micro-garden in a tropical climate can produce either 30 kilograms of tomatoes per year, 36 heads of lettuce every 60 days, 10 cabbages every 90 days or 100 onions every 120 days. This same square meter requires three liters of water per day, which, in certain climates, can be supplied by collecting and storing rainwater off a ten-square-meter roof. According to the F.A.O., kitchen gardens can be up to 15 times more productive than rural farms.
Of course, urban agriculture has obstacles to overcome, such as poor soil quality, air pollution, inappropriate use of pesticides and fertilizers that contaminate water, and biodiversity management.
25: The number of lettuce harvests per year in a high-tech vertical farm.
New Vertical Farms
In high-income economies, two methods have emerged for bringing agricultural production closer to cities. The simpler of the two is to use building rooftops and streamline collection and recycling of household waste. The second and more sophisticated method, deployed in countries such as Japan, South Korea, Singapore, the United States, and Canada, is soil-free vertical farming, which requires much less space.
There are two main forms of soil-free farming:
Hydroponics, the older of the two techniques, in which plants take root in an inert substrate, such as pumice, and are watered with a liquid nutrient solution containing mineral salts rich in nitrogen, phosphates, and potassium.
Aeroponics, in which plants are grown in plastic structures with their roots hanging in the air and exposed to vaporized nutrient solutions.
A variety of systems ensure closed-circuit water use, constant ventilation and exposure to natural or artificial light. The ability to control humidity and temperature ensures that plants grow four- to six times faster than they would using conventional farming techniques.
In the U.S. state of New Jersey, AeroFarms has developed farms where a head of lettuce can be grown in two weeks. Water recycling means the company consumes 95% less of the resource than field farms. Vegetables are grown without the use of any pesticides or herbicides, watched over by employees in cleanroom suits.
In Singapore, where limited space means that almost all food products must be imported, hundreds of nine-meter-high aluminum frames have been installed, around which plants rotate up toward the light, then down into troughs of rainwater.
Urban and peri-urban agriculture already provides for the needs of a quarter of the world’s urban population.
In Japan, which has six-times less farmland than France but double the population, large industrial companies are investing in vertical farming. For example, Toshiba has started a farm near Tokyo that produces 3 million bags of lettuce and spinach a year. The success of this type of agriculture is partly due to the Fukushima nuclear disaster, which led to concerns about vegetables being exposed to radiation. Some restaurants even offer greens grown before the customer’s eyes in miniature greenhouses.
Vertical farming has two drawbacks. First, because plants are grown on vertical shelves, there is an emphasis on smaller species, with grain farming excluded at this stage. Second, energy costs are high due to investment, equipment operations, and lighting.