Vinsamlegast notið þetta auðkenni þegar þið vitnið til verksins eða tengið í það: http://hdl.handle.net/1946/23208
In Iceland, winter production of greenhouse crops is totally dependent on supplementary lighting and has the potential to extend seasonal limits and replace imports during the winter months. Adequate guidelines for the most adequate lighting strategy (timing of lighting and light intensity) are not yet in place for tomato production and need to be developed.
An experiment with tomato (Lycopersicon esculentum Mill. cv. Encore, 2,5 plants/m2) was conducted from 13.09.2010-16.03.2011 in the experimental greenhouse of the Agricultural University of Iceland at Reykir. Plants in four replicates were grown under HPS lamps for top lighting with 300 W/m2 in one cabinet and with 240 W/m2 in three cabinets. Light was provided for max. 18 hours. During the time of high electrical costs for time dependent tariffs (November - February) one cabinet with the lower light intensity got supplemental light during the night as well during the whole weekend, whereas during the other months it was uniformly provided from 04-22 h as in the other cabinets, all the time. One cabinet received a daily integral of 100 J/cm2/plant and in addition per cluster 100 J/cm2 with 240 W/m2 supplemental light and natural light.
Temperature was kept at 22-23 ° C / 18-19 ° C (day / night) for cabinets with 240 W/m2, but 24-25 ° C / 20 ° C (day / night) for the cabinet with 300 W/m2. Carbon dioxide was provided (800 ppm CO2). Tomatoes received standard nutrition through drip irrigation. The influence of light intensity and of lighting at cheaper times on growth, yield and quality of tomato was tested and the profit margin calculated. At the end of 2010 plants showed zinc deficiency. It was decided to shorten the growth period from the cabinet with the highest light intensity. The accumulated marketable yield of tomatoes that received light during nights and weekends was lower compared to the normal lighting time. Also, when normal lighting time had been restored, the yield did not approach the yield obtained at normal lighting time with final yields amounting to about 15 % less yield. The yield decrease was mainly attributed to less fruits. Less light at the early stage of transplanting and lighting according to solar irradiation resulted in yield that was comparable to the traditional lighting system. Marketable yield was 94-97 % of total yield and was lower with the highest light intensity due to a high amount of cracked fruits. It seems that fruits with blossom end rot were increased at the highest light intensity and at lighting during nights and weekends.
There was no influence of the lighting regime on height, number of clusters, distance between internodes, DM yield of leaves, cumulative DM yield (yield of fruits, leaves, shoots) and N uptake by plants. However, if results from the cabinet with the higher light intensity were also included, the distance between internodes was there tendentially decreased and dry substance of fruits tendentially increased compared to the other cabinets.
The energy costs could be only slightly decreased with supplemental light during nights and weekends, whereas lighting according to the number of clusters and solar irradiation saved about 6 % of the energy costs. This resulted in an about 9 % higher profit compared to the traditional lighting system, while the profit with light during nights and weekends was about 18 % lower compared to normal lighting times. Possible recommendations for saving costs other than lowering the electricity costs are discussed. From the economic side it seems to be recommended to provide light at normal lighting times and not during nights and weekends. Energy costs could be decreased, when lights would be turned on for fewer hours at the early stage after transplanting and if supplemental lighting is done in accordance with the solar irradiation.