Because of all the sunshine, Dutch greenhouse vegetables have grown superbly this year. But the summery weather causes the cucumbers, tomatoes, and bell peppers to consume enormous amounts of water. Luckily, the Dutch growers are using water more and more sparsely. Did you know that to produce one kilo of tomatoes requires ten times less water than the same kilo in Spain?
Tomato grower Rimato is growing honey tomatoes on 14.6 hectare in Honselersdijk, and is officially a 'zero-waster': water that is not used by the plants, is collected in gutters and reused. To prevent waste throughout the year, the grower applies a number of clever tricks. Marcel van der Knaap is responsible and tells us more.
Wet start
Tomato plants are grown on rock wool mats, wrapped in plastic. At the beginning of a new growth, they are filled with water. After a few weeks the roots need air: the water that is not used has to be drained quickly. "We used to cut the mats open, now we make small holes in the plastic. The water is drained more evenly into the gutters, and we prevent overflowing."
Smart filtering
The gutter transports the water to large silos. UV light and a special filter is used to remove dirt and any diseases from the water. "This 'drain water' is then mixed with rainwater, which we collect in three rainwater basins totaling 32,000 m3. It is then returned to the plant with the right recipe of fertilizers."
Leakage
The gutters with rock wool mats are not attached to the ground: in this way the grower can closely monitor if there is any leakage. "We also regularly measure the ground water and ditch water. Do we measure too much fertilizer? We are probably dealing with a leakage, and we can quickly find it."
To the last drop
One time a year all plants and rock wool mats are replaced. To prevent waste of water in the end phase, it is essential to remove these as dry as possible. "Shortly before the end we are already reducing irrigation, and the water we reuse is extra water from the drain water silos. At the end of the growth they are empty, and we can start the new growth with clean water from the rainwater basins."
More can be done
Before this can happen, the greenhouse has to be thoroughly cleaned, which is done with cleansing agents... and lots of water. "Luckily the cleansing agents are getting better and better, so we can save more water. In this way, we keep on making steps towards a clean, sustainable cultivation."
Source: LTO Glaskracht