LED technology brings flexibility to cultivation of forest tree seedlings.
In Finland, forest seedlings are mainly cultivated using natural light. Some nurseries use artificial lamps in order to lengthen the natural photoperiod in the spring. This prevents premature cessation of height growth and bud formation.
The development of LED lights and the fall in prices as well as greater knowledge about the effects of different wavelength ranges on plants enable new applications also in nurseries that cultivate forest seedlings.
LED lamps are durable and lightweight, and produce a favourable wavelength distribution for light. The new technologies enable seedlings to be grown even without natural light.
In Sweden, pre-cultivation of seedlings in closed cultivation units using LED technology is being developed. After transplantation, subsequent growth takes place under natural light.
“Pre-cultivating seedlings in a closed area in several layers naturally saves heated space, and the initial development of the seedlings is uniform,” says Johanna Riikonen, a senior scientist at Natural Resources Institute Finland (Luke).
Compared to traditional plastic greenhouse cultivation, this new method brings flexibility to seedling production, as it is even possible to cultivate seedlings all year round.
LEDs enable different wavelengths of light to be used optimally.
Photosynthesis is most efficient at light wavelengths between 400 and 500 nanometres (blue) and from 600 to 700 nanometres (red). The red to far-red radiation ratio (700 to 800 nanometres) affects the morphology, growth rate and growth rhythm of seedlings.
“By increasing the proportion of blue radiation, the height growth of seedlings can be regulated and by decreasing the amount of far-red radiation, the ability of seedlings to withstand dryness can be improved. As a shade-intolerant species, pine is more sensitive than spruce to changes in the quality of light,” Riikonen thinks.
The benefit of LEDs compared to high-pressure sodium lamps is their greater ability to convert electricity into light and their lower heat production. The lamps can be installed closer to the plants, enabling them to utilise light energy more efficiently. This enables multilayer cultivation and inter-lighting, which increases the efficiency of the use of space.
No disadvantages to the use of LED lights have been identified. Cultivation lamps with high levels of blue light can cause a risk of eye damage when the light hits the retina over extended periods of time.
The lamps should be directed away from the field of vision. When cultivation lamps have high levels of blue radiation, employees should use protective eyewear.
“The irrigation routine is somewhat different, as LED lighting does not generate heat in the way that traditional high-pressure sodium (HPS) lamps do. The surface of the peat remains cooler and more moist, allowing lichen and algae growth to develop on top of the cell trays,” Riikonen says.
LED lights are still expensive, however, and for this reason their use has not proliferated. LED technology will increasingly enable production to be moved from greenhouses to closed spaces that can be termed plant factories or closed plant production units.
“LED technology will bring the greatest change by enabling the quality of light to be flexibly modified according to wavelength. In the future, the optimal use of different wavelengths may, among other things, improve seedling stress resistance, lower disease risk and reduce the use of pesticides,” Riikonen envisions.
Text: Aimo Jokela, Luke
Photo on top of the page: Johanna Riikonen, Luke.
Published in Finnish in Maaseudun Tulevaisuus 3 of April 2017.