The use of LEDs can be promising for greenhouse horticulture, but before it can be put into practice on a large scale more knowledge must be acquired on effects of LED lighting on crops. Furthermore, the growers will have to learn to grow their crops under LEDs and the efficiency of LEDs must increase even more. In order to gain more insight into the influence of LEDs on crop growth and production, an experiment was performed in the Wageningen UR greenhouses with a small Santa type tomato ( Differences in production were small, although the production under all LEDs was lower. There were only small differences in fruit quality. The amount of energy required per kilogram tomato was highest in the LED treatment and hybrid with top LED lighting. This was primarily due to the fact that a higher air temperature was necessary and these LEDs were cooled and the cost of cooling added to the use of energy. The consequences and future perspectives of the different types of supplementary lighting for crop growth and production as well as for crop management practices will be discussed.
INTRODUCTIONThe use of LED assimilation lighting can become an important player in greenhouse horticulture if energy efficient LEDs can increase production in the winter. However, before LEDs can be broadly applied in horticulture, more knowledge is necessary on the effects of LEDs on crops, how to manage crops growing under LEDs and how efficient they really are, not only in terms of light output, but also in relation to crop production. While the energy efficiency of LEDs is the result of technical improvement, knowledge on the effects of various lighting systems with LEDs on greenhouse crops and crop management as well as the efficiency of LED lighting per unit production must result from experimental research. To date, in experiments with LED lighting systems in greenhouses problems with crop growth and physiology have been encountered and are thought to be due to insufficient tuning of crop cultivation to assimilation lighting with LEDs (Nederhoff et al., 2010). These problems seem to focus on plant temperature, plant load and the influence of LED lighting on plant morphology
Heathland is currently being threatened by nitrogenous atmospheric deposition, mainly NH y (NH 3 and NH 4 "). Deschampsiaflexuosa and Calluna vulgaris in monocultures were well able to use NH y for biomass production, although in the case of C. vulgaris only shoot growth was stimulated and C. vulgaris increased its sensitivity to drought and the heather beetle (Lochmaea suturalis). In a mixed culture of C. vulgaris and D.flexuosa, the latter species was the better competitor for NH y • The relation between stimulated biomass production and increased stress sensitivity also applied to several other heathland species.A general effect threshold for adverse effects of NH 3 on plants has been established with a toxicological model: 270 and 8 J.1g m -3 for a daily and annual mean, respectively. Heathland species are relatively sensitive to NHy"
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