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More compact tomato young plants with a broad spectrum – Valoya trial in Sweden

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More compact tomato young plants with a broad spectrum 

Is it possible to get high-quality tomato young plants with LED lights, with fewer energy costs than HPS lights?

At Valoya, research plays an essential role in our business decisions; therefore, trials and their results are crucial for primary data. During winter 2022-2023, we at Valoya have conducted several trials with our customers. In this blog post, we will discuss the results of a test made in Sweden at Göinge Fridhem Trädgårds.

Background of the trial

For this trial, we chose the spectrum Solray385, used for crop production, where artificial light is needed to secure quality and sufficient yield. In the Nordics, the DLI (Daily Light Integral) can be as low as 1 – 5 mol·m-2·d-1 during winter. According to different sources, DLI for young tomato plants is 8 – 18 mol·m−2·d−1, depending on the growth stage. Therefore, supplemental light is essential.

Quite often, LEDs used in greenhouse production are blue and red. The blue and red wavelengths are the most efficient, considering photosynthesis, plant development, and prices. Still, the other wavelengths also have an essential role in plant growth. The wavelength is critical when there is little or almost zero natural light. It is also not comfortable to work under only blue and red LEDs. Their CRI (color rendering index) value can even be zero when sunlight’s CRI is 100. The CRI value of the Solray385 spectrum is 90, which makes working under the broad spectra less uncomfortable for the eyes, and for the worker, it is possible to see the plants as they appear. Such clear visibility is vital for quality control and observing likely insects or diseases in the plants.

Solray385 is a broad spectrum, including all the wavelengths from UV to far-red. Depending on the dosage and wavelength area, UV wavelength can be dangerous to plants. In small dosages, both UV-B and UV-A increase the stress tolerance of the plants. Generally, plants that have grown under ultraviolet light have thicker canopy and stem and, in addition, shorter internodes. Solray385 contains a small amount of UV-A, which is not harmful to plants or humans.

Fig. 1 Solray385 spectra in picture

The start of the trial

The trial started on 18.1.2023 when we transferred the young plants to the greenhouse and installed the LED fixtures. With the owner of the greenhouse, Erik Lerbs, we conducted the trial at Göinge Fridhem Trädgårds’ greenhouse in Sweden, Skåne. After the test, the plants will be moved to their final cultivation area and planted within a few weeks. We had numerous participants in the trial, including HPS and a competitor (X).  The Valoya fixture used was RX325 with two spectra, S2 and Solray 385. X and Valoya S2 are mainly blue and red spectra. They both have a small amount of green for a more pleasing eye appearance. Still, both lights appear very purple.

Fig. 2 Appearance of different spectrums

All the plants were irrigated and fertilized the same way in the whole room during the trial. The grower used Grodan rockwool cubes for the plantation, the most used growing media for young tomato plants. Young plants were the same variety as ‘Tomicia’ from RijkZwaan.

Fifteen plants were chosen for each light treatment for the trial and positioned under as similar intensities as possible. The target light intensity was 110 µmol/m2/s1, and we measured the seedlings’ initial height. We conducted light measurements and installed wireless PAR, temperature, and relative humidity (RH) sensors (Aranet) in every trial area for improved stimulation accuracy and constant follow-up. One sensor was placed on top of the fixtures to measure the light coming from the sun to the greenhouse.

Final measurements 

At the end of trial 8.2.2023, we measured the height and the length of the third real leaf from the plants. Plants under Solray385 were shorter, stronger, and more compact compared to other spectra.

We observed the plants’ color and leaves; they appeared to be darker and more uniform under Solray385. We measured the leaf temperature to be between 21-23 °C in every light treatment. Temperature and RH were maintained at the same level regardless of the trial area.

Fig. 3 The light is comfortable under Solray385

Conclusions based on the trial results

Although the trial time was short, it was evident that the plants under the Solray385 spectrum were more compact and stronger. The energy costs were decreased compared to HPS. Three weeks is a standard time for young tomato plant cultivation. The benefits of stronger plants are:

  • Less plant loss => better profit
  • Plants are easier to handle => less time to move the plants
  • UV-resistant: plants get UV light from the spectrum.
  • More durable cell structure => better resistance to diseases

The plants were transported to the final cultivation site after this trial. The observation will continue during the growing season. The differences between different light treatments will likely become less steep in the greenhouse after a few weeks.

Do you want to learn more and get more information about the trial? Contact our sales:  sales@greenlux.com

The blog posts are written by Valoya’s biologists and engineers. All of the content is original and is aimed at helping growers and researchers get a better understanding of the LED grow light technology.

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