During the 2015/2016 indoor growing season, the Greenhouse Horticulture business unit of Wageningen University & Research grew tomatoes under LED lamps with additional far-red light. This resulted in increased production and provided enough evidence to begin practical testing. Two weeks ago, far-red lamps went into use at Prominent I and the first effects can already be seen in the crops.
During the study, which was performed in the previous indoor growing season by the Greenhouse Horticulture business unit and Philips, a grafted/topped tomato plant (Komeet variety) was grown under 185 µmol/m²/s LED light. There were two additional treatments, in which 30 and 55 µmol/m²/s far-red light was added. This resulted in a 6% increase in production when 30 µmol/m²/s far-red light was used and a 15% increase when 55 µmol/m²/s far-red light was used. This production increase was primarily due to a higher average fruit weight.
Testing on a practical scale
For the tomato producers who visited this testing site a number of times, these results provided sufficient reason to want to see testing on a practical scale, where far-red light was used in addition to SON-T lamps. For this reason, in November 2016, practical testing was begun at Prominent I in which four testing boxes, each 25 metres in size, were set up in the greenhouse. One of the boxes is lit with 30 µmol/m²/s far-red LEDs placed above the plants, while in another, the same light intensity is used, but between the plants. For Kas als Energiebron (Greenhouse as an Energy Source), it is important to look at the extent to which low-intensity far-red light could replace assimilation light in order to save electricity. For this reason, a box was also set up in which 10 µmol/m²/s far-red lamps were placed between the plants. The fourth testing box serves as the control, so no far-red LEDs were used.
Measuring the effects
In the months to come, the effect of the far-red light on the plants should be demonstrated. Based on the results from last year, we expect that the crop will grow higher and the leaves will be less green. However, the tomatoes that are harvested will also be heavier. We will have to wait and see whether this will be the case. In the test, the plant length and leaf length is measured weekly. This has shown that after the first week, the plants under the far-red light were a centimetre longer than those without additional far-red light. This means that the far-red light, in conjunction with SON-T, has an effect on the plant. How this will play out will become clear in the months to come.
This project is funded by the producer associations Harvest House, Prominent, Tasty Tom, Lang, RedStar, and The Tomato Company, as well as the Kas als Energiebron programme. This is the innovation and action programme of LTO Glaskracht Nederland and the Ministry of Economic Affairs. Ω
Posted 20 December 2016