| Summary: | 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 increasing yield are not yet in place for tomato production and need to be developed. The objective of this study was to test if interplanting, deleafing and pruning the clusters are affecting growth, yield and quality of tomatoes and to evaluate the profit margin. Two experiments with grafted tomatoes (Lycopersicon esculentum Mill. cv. Encore) were conducted, the first (A) from October to the middle of January and the second (B) from the middle of January to the middle of June 2014, in the experimental greenhouse of the Agricultural University of Iceland at Reykir. Tomatoes were grown in pumice in four replicates with 2,66 tops/m2 with two tops per plant under high pressure vapour sodium lamps (HPS, 240 W/m2) for a maximum of 18 hours light. The daytemperature was 21,5°C and the night tempera ture 18°C, CO 2 800 ppm. Tomatoes received standard nutrition through drip irrigation. In part A was the effect of pruning the clusters and deleafing tested and the profit margin calculated, in part B was the effect of interplanting and deleafing tested and the profit margin calculated. Pruning of the clusters had an effect on marketable yield, the harvest was 10 % less. The average fruit weight was higher with pruning the clusters, but the amount of harvested fruits was lower. More fruits were classified as first class fruits after pruning the clusters and too small fruits were decreased. Fruits from the treatment without interplanting were harvested about one week earlier and with longer growing period increased the yield (35 kg/m2) more than with interplanting (30 kg/m2), which was a significant difference. But, without interplanting could no fruits be harved during the time the old plants were moved out of the greenhouse and the new plants started to give the first harvest, which was about 8 weeks without ...
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