A tomato flat: growing vegetables in the city

Urbanization is increasing worldwide. To supply the growing populations in cities with fresh vegetables, Wageningen horticultural specialists are conducting research into vertical farming. With this technique, crops are grown indoors year-round with the help of LED light and in layers on top of each other. Land and water use decline enormously, and pesticides and shipping over far distances are a thing of the past. The researchers are looking at how vertical farming can be more energy efficient, and the vegetables even more nutritious and tastier. Is a tomato flat a good idea?

Vertical farming takes place in buildings – the crops are grown on top of each other in several layers. “In a high-rise building – on a surface area about the size of a soccer field – you can grow enough vegetables for 100,000 people who each eat 250 grams of vegetables a day. You have complete control over the production process, so you are not dependent on the weather, the temperature, the daylight and the season. This makes vertical farming possible everywhere – also in infertile areas, in the desert or on Mars”, says Leo Marcelis, professor of Horticulture.

“Vertical farming will not solve food shortages. It does not lend itself to rice and cereal production, but it is good for healthy, fresh vegetables, packed with fibre and vitamin C, and grown without contamination by pesticides or harmful microorganisms. That makes vertical farming one of the solutions to the global food issue”, says Marcelis.

“If we coordinate the amount, colour and duration of light from the LED lamps, the amount of water and the temperature and composition of the air very precisely, we can give the crops much more nutritional value. In addition, we can also improve taste and shelf life.”

Vertically grown vegetables can make do with much less water. “We can recycle all the water and recover most of the water that the plants evaporate. As a result, we only need two to four litres of water to grow a kilo of tomatoes, whereas we use 17 litres of water in a Dutch greenhouse and in theory at least 60 litres for soil cultivation in for example southern Europe, and in practice often 200 litres,” says Marcelis. In the closed cultivation system, nutrients such as nitrates and phosphates are also retained, while outside cultivation they end up in the soil, groundwater and surface water.

Is LED light healthy for plants? Surely there is nothing better than sunlight? Marcelis is regularly asked that question. “If we adjust the amount, colour and duration of the light, the amount of water and the temperature and composition of the air very precisely, we can give the crops much more nutritional value. I am absolutely convinced of that; there is already evidence that these factors influence nutritional value. In addition, we can also improve taste and shelf life.”

Energy usage
However, vertical farming also has disadvantages, and that is mainly due to the relatively high energy consumption. “Even though LED lamps are economical, a quarter of the costs goes to energy consumption. If you can make substantial savings on this, the investment will become more affordable,” says Marcelis. Together with colleagues, he is studying options for reducing energy consumption. “We want to ensure that the light is used more efficiently by the plant. If we can optimize the temperature, humidity, concentration of carbon dioxide and availability of water and fertilizers and can determine the optimum intensity and colour of the light for every moment of the day, we can produce much more per unit of light,” says Marcelis. He also wants to improve the efficiency of climate control technologies.

Read more at Wageningen University & Research

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