| Summary: | Rit LbhÍ nr. 40 Final report of the research project „Effects of lighting time and light intensity on growth, yield and quality of greenhouse tomato“ 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 ...
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