Hydroponic lettuce and circular tomatoes

There are always trials in progress at 'de Kas'. The team of R&D specialists and laboratory technicians perform various trials and analyses in the twelve trial sections in the greenhouse, outdoors and in the extensive laboratory. Their work delivers valuable knowledge and experience of different crops and cultivation systems, so van der Knaap can support its customers by providing the right products and appropriate advice.

Hydroponic lettuce
Van der Knaap have been conducting trials growing lettuce in a hydroponic system for a number of years. Until recently, the company only used a trial set-up with water basins; the deep float system. Van der Knaap sow the lettuce in Obturo plugs and grow the plants themselves.

© Van der Knaap Diensten BV

After the rooting phase, the plants are transferred to the water basins. Up until now, the main goal was to compare the effect of the standard mineral nutrient solution with the organic nutrient solution from the bioreactor - the organic water system (OWS). Van der Knaap can now inform that this nutrient is effective. The results are similar to those of conventional fertilizers which means the trials will continue exclusively using the organic nutrient solution.

Obturo
Obturo® is an extremely versatile plug with a unique composition. The plugs have a high germination rate due to the excellent air-water ratio and contain a balanced nutrient composition for a good start. In addition, they minimize contamination in the system and their dimensional stability makes them ideal for automatic handling systems.

Gutter cultivation system
Growing in cultivation gutters is becoming increasingly common. To widen the experience and knowledge of this system, van der Knaap have been running trials with lettuce on a gutter system since 2024. The PB-TEC system, in collaboration with VH Systems, consists of gutters and extra-long paperpots made to fit the system. The trial demonstrates the possibilities of using the nutrient solution from the OWS. Van der Knaap are also focusing on developing the right combination of substrate and paper to grow lettuce in a hydroponic system.

Circular tomatoes
There is a rising demand for more sustainable cultivation methods. To investigate the possibilities, van der Knaap set up a trial in 2023 using materials that could be composted after cultivation. After the trial, the (cultivation) material was industrially composted - in tunnels - at a specialised company. The materials were composted without being chopped or ground first. The twine proved to be fully compostable and the film for approximately 95%. Treating the materials before composting is expected to improve this percentage to 100%.

During the trial, researchers noticed that some tears appeared in the film along fold lines. This indicated potential for improvement so they planned a follow-up trial in 2024 which used an improved version of the degradable film. This follow-up examined aspects including the aging rate of the film. The substrate (coco) and the twine (supplied by Hortiware) were both circular products. Researchers also added circular CaNO3 produced by the organic water system (OWS) and used biological pest control. Although these trials aim to reveal new insights into the various possibilities, the cultivation process and yield are just as important. PLFA analyses were therefore used to identify the differences in soil life.

New trial
A new trial with tomatoes is scheduled in 'de Kas' this year too. The main focus will be researching the substrate. Forteco Optimum coarse is a new type of coco substrate growbag, distinguished by the addition of finer chips to the mixture. The researchers expect this to result in faster rooting. To date, the root system has been developing well in this substrate. Researchers replaced the conventional liquid calcium nitrate by circular calcium nitrate (HNCN) produced by Van der Knaap.