Last year Van der Knaap Groep performed two different trials with hydroponic lettuce. Karel de Bruijn: “We used mineral nutrients in one pond and organic in the other. Last year's trial was successful. The filtration system did its job. The membranes ensure the bacteria can't pass through. That's why our nutrient solution is free of bacteria and fungi.”
The trial was successful for both mineral and organic fertilizers. This makes the nutrient solution suitable for a hydroponic system. Karel: "When you dissolve organic fertilizer pellets in water, the water becomes anaerobic. It will start stinking and the pond fills with muck. We use a filtration step in our system, which keeps the water free from anaerobic bacteria. Therefore, it is very suitable for hydroponic systems.”
"The trial has been promoted"
Last year's results showed that the yield is quite good compared to the mineral cultivation. This year, Van der Knaap chose to do trials with four ponds instead of two. "The trial has been promoted to another department. We have two ponds with a lower pH and two ponds with a higher pH. Why do we do that? With the bioreactor, we can control the pH through the bacteria. If we keep the pH between 5.5 and 6 by adding 4.5, the growth rate and production remain good,” says Karel.
The trial started 2 months ago and will last about a year. Karel: "In winter, a cycle of lettuce takes about 3.5 months, in the summer about 4 weeks. We cultivate year-round so we can see everything and rule out eventualities.”
To the question of whether hydroponic lettuce is the future, Karel de Bruijn and Ron van der Knaap replied with a resounding: “Yes!” Karel explains: "The yield per square meter is so much higher and it takes less work than open-field lettuce. All leafy greens such as herbs, lettuce, etc. are perfect for hydroponic systems."
Innovation Center 'De Kas'
In Innovation Center 'De Kas' from Van der Knaap, trials are done with different vegetable crops. This involves various types of substrate and mineral versus organic nutrients.