There will be an expansion of the multi-layer strawberry cultivation trial at Research Centre Hoogstraten. Currently, the last winter cultivation harvest is in full swing. After the harvest, researchers will lay out the design of the next trial. Although there is no exact setup yet, the next trial will certainly have 18 rows of 3/4 layers (instead of 6 rows).

This cultivation setup has been in the greenhouse complex since 2019. This bright pink LED-lit strawberry 'stack' will be visible from the road near the greenhouse complex from late January onwards. This winter, researchers will harvest the Sonata variety (which was planted in October.) Aside from winter cultivation, June-bearers were already tested in the system throughout all seasons. Everbearers have not yet been tested.

Stef Laurijssen explains: "From all earlier cultivations, We have learned that real winter cultivation works best thanks to the LEDs which allow for maximal control. "Some seasons are more suitable for our multi-layer cultivation than others. Lower layers perform less well when there is a lot of natural light. It can,, for example,, lead to fruit deformation".


The 4-layer strawberry cultivation at the start of week 5

Lighting
Initially, researchers had some difficulty with finding the right LED lighting for the multi-layer cultivation trial system. However, nowadays, lighting is well-managed, and the trial space is split into two parts. One of these is equipped with Luminaid fixtures with a maximum of 300 micromol/(m2.s). The other part is equipped with MechaTronix fixtures with a maximum of 340 micromol/(m2.s). Both fixtures are dimmable.

"The spectra for the two different parts are nearly the same," says Stef. Both fixtures are far-red as far-red strips were added to the Luminaid fixtures (far-red was already in the MechaTronix lighting). Another difference is the beam angle. "Whereas Mechatronix has a 120-degree angle, Luminaid fixtures have one of 90 degrees. The advantage of the larger angle is that the fruits in the adjacent row also receive lighting. That helps with the fruit's coloring process."

The second row from below with red, ripe strawberries on the left.

The RH challenge
The coloring of the strawberries is not an issue in January. This is especially visible in the rows that are not yet harvested, which have many ripe red strawberries. Maybe even a little too much, Stef admits.

At the top, we find vertical fans which according to Stef are "a try".These were left-over fans from another compartment, and we wondered whether these could be useful in this setup. Unfortunately, they are not: the plants in the top row are affected too much by the air movement."

The vertical fans are used to reduce the relative humidity (RH) at the bottom of the system. In multi-layer cultivation, RH is a true challenge because RH increase at the bottom can cause fruit rot. "Last growing season, we worked with vertical fans and an air hose. This is not common for a horizontal application, but this way, we managed to achieve a more homogeneous climate in the different rows."


The vertical fan produces too much air movement at the highest row. In 2023, trunks were more effective.

Optimal lighting
Further, the cards with numbers stand out. The researchers have divided the gutters into research objects, during the current winter cultivation they examine various cultivation strategies. The target is to find out how energy savings can best be achieved.

A winter crop with Sonata (planted in October) has a total light requirement of 1900 mol/m2. Using a lighting table, the light sum is distributed over the different stages of the cultivation. When the plant is in full production, this can be up to a maximum of 18 moles per square meter per day. The researchers also take into account the incidence of natural light.

In the 4-layer system, the light incidence quickly decreases. Only 35% remains on layer 3. "We initially thought it would be 50%, but we soon found out that it was even less." For layer 2, 10% remains, and for layer 4, only 5%. For this reason, the researchers choose to have more lights in the bottom rows."


The gutters are divided into different research objects. The research is concerned with energy savings.

Strategies for energy saving
For the energy savings research, researchers are testing various strategies this winter within the Opti-Energie project (VLAIO LA project). When it comes to electricity, the most expensive hours are usually between 7-11 a.m. and 5-7 p.m. During these hours, the lights go off in the cultivation setup. "We are investigating how electricity cost-savings affect plant growth." Another strategy is to reduce the number of mills from 1900 to 1800 ( or even 1600). It could also be an option to reduce the number of lighting hours per day. Maybe 14 hours of exposure (rather than the more common 16) is also possible.

After this ongoing winter cultivation, the researchers can share their results. During 2024's follow-up trial, researchers will also consider active dehumidification. In 2025, they hope to start a new cultivation round in this more extensive setup.

By then, the test center will also have a department where daylight-free starting material for strawberries will be grown. "Will cover a section of a greenhouse with sandwich panels," says Stef.

In addition, there are plans for an expansion. During our visit to the test center in Meerle, an old greenhouse had just been demolished. It will be replaced by 1.4 hectares of new greenhouse. The researchers are still holding co-creation sessions with growers and technology parties. During these sessions, they discuss the exact design of the new greenhouse. "We hope to plant strawberries in that greenhouse in mid-August."


Research Centre Hoogstraten gets a new greenhouse.

For more information:
Stef Laurijssen
Research Centre Hoogstraten
stef.laurijssen@proefcentrum.be
www.proefcentrum.be