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Lesson from tests with new LED fixture: Graph for absolute humidity must be on

"Ary, you're in the greenhouse again, aren't you?" Ary de Jong of HortiTech has regularly received comments like these over the past eighteen months. People are surprised that he has returned to doing cultivation tests in the greenhouse after transferring from Demokwekerij Westland to HortiTech.

The reason is simple: Climalux, which is launching a new LED fixture on the market, wanted to do some tests, and HortiTech can help. COVID-19, however, threw HortiTech's plans into disarray. Turning 'managers into horticultural entrepreneurs' and providing remote global guidance to new horticultural companies was temporarily hampered, creating extra hurdles on the way. However, newcomer Ary turned out to be the perfect man to jump over these hurdles.

Ary de Jong of HortiTech and Laura Frijters of 2Grow in the cucumber trial with the Climalux fixtures

Absolute moisture
The Climalux fixture is equipped with a fan and appears to require a new way of growing. Sensors, including 2Grow's sap flow sensors, are an important tool in this, as they provide real-time insight into the absolute moisture content. In fact, Ary managed a summer crop of cucumbers almost entirely on the basis of this 'new line to play with'.

"I have to admit that I've never actually looked at the absolute moisture content before. And I'm not the only one, I know from experience," Ary laughs. He has now done three crops with the new lamp, in addition to the current cucumber crop and a winter crop of tomatoes and cucumbers. A fourth crop is on the way. 

The Climalux fixture is a light fixture that is equipped with a fan that helps cool the lamp and pushes the air vertically from top to bottom, creating a constant air movement in the greenhouse. "That is different from the traditional way of growing that you often see nowadays." Moreover, it is possible to create an airflow that blows warm air down, but also to introduce heat to the top. Ary calls it 'an extra steering possibility'.  

Understanding plant activity
Ary's inexperience with the new way of growing means that the 'new' data is of great help. The sap flow sensor from 2Grow, and cultivation guidance from service manager Laura Frijters, help him with this. Laura: "One of the shortcomings of LED lighting is the lack of heat in the top, making it more difficult to get the plant sufficiently active. However, this is difficult for growers to see with the naked eye, let alone to see it quickly. We can make this visible in real-time by placing sap flow sensors at the bottom of the plant."

In search of the optimum
Ary and Laura have very intensive contact during the trials. Ary: "There have been many occasions when I thought I was making good adjustments using my experience, only for Laura to say: 'What are you doing?' Then it turned out that she could already see from the sap flow data what I was doing, without looking into the greenhouse. It turned out I was dehumidifying too much at night, without being able to see the effect on the crop. How long and how much I have to chill now, that's what the figure on absolute humidity tells me."

An earlier cucumber trial with the Climalux fixtures in 2020.

Of course, it is not (yet) the case that when the figure for absolute humidity starts to move, it is immediately clear what's 'wrong'. "That would sure be something, if the new line in my climate control system immediately showed me where I had to adjust something," Ary laughs. "However, I am certain that if I see that the relative moisture content is 'good', but the absolute moisture content is not, that there is a production gain to be had."

For more information:
Ary de Jong 
[email protected] 

Laura Frijters
2Grow bvba 
[email protected]  


[email protected] 

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