Energiezuinige full-LED-tomatenteelt zonder wankleur

Cultivation continues through week 17, but after three years of research, the results of a major study in illuminated tomato cultivation were already shared in early April. One of the conclusions: it is entirely possible to grow healthy tomatoes under full LED lighting with a 50% lower heat input. Positive news for growers in practice, although one of the growers present at the panel discussion on Wednesday rightly added a caveat.

Grower Jan-Willem Bolle of Noordhuys sees a danger in drawing conclusions too easily from research in response to the energy crisis of 2021-2022. Policymakers in The Hague are reading along too, and they could easily miss the much-needed nuance that accompanies such a striking conclusion. The tomato grower with 11.5 hectares of LED cultivation, for example, points out that there is no cost associated with the realized crop. He also notes that while the researchers were able to push the boundaries—for instance regarding fertilization—practical growers cannot take those risks. If something does go wrong, the financial damage on sometimes tens of hectares can easily run into the hundreds of thousands. Copying research to practice is not a simple matter.

Practical Tools
The researchers and those present in the room acknowledge the practical concerns of the tomato grower. Under the leadership of Signify and Grodan, research was therefore set up three years ago specifically to provide growers with practical tools derived from the research to optimize full-LED cultivation.

Cherry tomatoes were grown in the study during the first two years. In the third year, at the request of the industry, a large truss tomato was grown: the Macxize variety from Axia. Also new in the third year of the study is special attention to color defects, and the introduction of interlighting is also new. On Wednesday morning, participants were first able to visit Botany to view the trial, and also to smell and feel the tomatoes in the trial. In the afternoon, results were shared in more detail by various speakers. The program included presentations on light and climate, as well as on irrigation and the nutrient strategy.

A look inside the 256-square-meter greenhouse at Botany. The 30-week cultivation started in week 39 and runs through week 17. The Macxize variety from Axia was grown on 3.73 stems, maintaining five fruits per truss.

Distortion and light utilization efficiency
Concluding the event was the panel discussion. In addition to grower Jan-Willem, the panel included trial leader Bram Rongen from Botany, Evelien Rossiers from the Research Station for Vegetable Cultivation in Sint-Katelijne-Waver, and cultivation advisor Willem Valstar from Stargrow Consultancy. Based on questions from moderator Matthijs van den Beukel, the bridge from research to practice was built.

Matthijs, who, like myself, joined the program halfway through, immediately noticed that the topic resonated strongly with the attendees. Upon entering the Graaf ter Horst conference venue in Horst, attendees were busily writing in notebooks, typing along on smartphones, and asking plenty of questions during the presentations.

During the panel discussion, current points of attention such as discoloration and light utilization efficiency under LED were addressed. It is striking that the researchers have been able to reduce problems with discoloration in their cultivation using low heat input.

Adjusted nutrition strategy

Moreover, an adjusted nutrition strategy has contributed to maintaining high-quality large truss tomatoes. In winter cultivation under LED, an approach was found not only to understand green spots and discoloration, but also to predict and prevent them. By focusing on factors such as a higher potassium/nitrate ratio and a lower EC, both production and quality remain guaranteed, as demonstrated by Ruud Kaarsemaker of Normec. In the study, extensive measurements were taken using sensors from Wireless Value and Grodan, among others.

Interlighting
Technically, the use of interlighting alongside overhead lighting stands out. Two light treatments were tested in greenhouses containing Ridder screens. One treatment involved only 350 micromol Philips top lights, and the other treatment consisted of 247 micromol overhead lighting and 103 micromol Philips interlighting.

With the latter light treatment, a production increase of 5-7% could be achieved. According to commercial growers, this is not yet enough to justify the investment in their greenhouses, but it may well be a reason for new research. For example, it would be interesting to compare the use of interlighting with the use of an extra grow tube higher up in the crop. In terms of investment, that extra grow tube is currently the easiest to implement, but what if even more production increase is possible with interlighting?

Dehumidification

Automatically, the panel discussion also touches upon policy—which must be stable for growers to be able to invest, Evelien emphasizes—and upon crop protection, providing fodder for at least another hour of discussion. That is not the direction things are heading on Wednesday. The focus remains on energy-efficient tomato cultivation under full LED lighting. According to cultivation advisor Willem, dehumidification has become a must in this regard. The researchers also had this at their disposal in the Botany greenhouses. The Air&Energy system was used, which also allowed for the creation of air movement.

The results of the study were shared with a Dutch-speaking audience on Wednesday. Philips and Grodan will also share the results with an international audience during GreenTech Amsterdam. Furthermore, they will share additional research results, including figures, once the entire cultivation period is completed after week 17.