News - July 5, 2017

Cultivating lettuce on polystyrene

Didi de Vries

If you think that lettuce can only be cultivated on soil, you might want to think again. It can also be done on rivers and lakes, thanks to islands made of polystyrene. Wageningen Plant Research in Lelystad is experimenting with this method of cultivating crops.

© Sören Knittel

Cultivating vegetables on floating material might offer a solution for areas that flood regularly. ‘Or for agricultural land that is used for water storage during high water’, says Marcel Vijn, researcher Urban-Rural Relations at WUR. He is studying the possibilities of cultivating crops on floating polystyrene.

Stichting Drijvende Eilanden (‘Floating Islands Foundation’) and Wageningen Plant Research are conducting trials with a test island in Lelystad. They wrap blocks of polystyrene in plastic film and bind them together using nets, thus creating rafts of two by three metres in size. The whole floats in a specially designed basin. Cylindrical holes have been put in the polystyrene, in which lettuce, spinach and tomato plants have been suspended. The roots are in direct contact with the water, allowing them to absorb water and the nutrients it contains.

Water levels
With the polystyrene crops, the foundation wants to make use of high water levels. Vijn explains: ‘Bulb cultivators can temporarily flood their land in their fight against roundworms, but that also forces them to stop production. With options for floating cultivation, they could have a non-zero production.’ Besides, there are areas in the Netherlands that are flooded during high water and could be used for ‘Floating Food Farms’.

When you are in the greenhouse, you don’t realise you are floating on water, because you are standing on a solid floor.

The concept is not entirely new. Some farmers already use polystyrene sheets to cultivate vegetable on. But this is only on racks in greenhouses and not directly in open water. Another floating variation is a greenhouse for demonstrations near Naaldwijk in Westland. That greenhouse was built in 2005 and entirely on floating materials, because the area stores water in times of heavy rain. ‘When you are in the greenhouse, you don’t realise you are floating on water, because you are standing on a solid floor.’ This differs from the initiative of Stichting Drijvende Eilanden, in which the plants float directly on the water surface and the farmer walks through the water or over a floating bridge to reach them.

© Sören Knittel

The Floating Food Farms are not only interesting for farmers. Innovative restaurants are also a target group of the foundation. A dinner with fresh home-grown lettuce is appealing. ‘Think of a city like Singapore, where there is very little agricultural land and where the prices of agricultural products are high’, says Vijn.

Floating Food Farms could also provide a new source of income in poor areas with rivers and lakes. Better yet, floating cultivation grounds are already produced using water hyacinths in Bangladesh. Farmers rake together the rampant water plant and use it to create a mattress that sticks out of the water. On top of that surface, they lay soil in which they can cultivate vegetables. The hyacinths slowly rot, thus providing the crops with a proper nutritious soil to grow on. The drawback of the rotting is that farmers constantly need to create new cultivating mattresses. A time-consuming job that could be prevented with polystyrene islands.

According to Vijn, replacing the organic material with a product of crude oil is not necessarily a problem. ‘Polystyrene mainly consists of air and a little bit of oil, and can technically be recycled’, he says. ‘It becomes a problem when people start discarding the polystyrene everywhere. If you prevent it from getting into the environment, it doesn’t have to be so bad.’