M.J. Verheul, H.F.R. Maessen , S.O. Grimstad
The use of supplementary light is necessary to assure year-round production in northern countries. In Norway the use of artificial light is favored by a long winter season, a mild climate along the coastline and the availability of hydroelectric energy. Earlier experiments and practical experiences have shown that the use of artificial light increased cucumber production from 40 to 180 kg m-2. The goal of this research was to optimize the yield potential of tomato production under supplementary light. In 2003-2004, production potential using artificial light (with a photon flux density of 220 µmol m-2 s-1, provided by 400 W SON-T lamps during 18 hours a day) was investigated using a cropping schedule of three plantings a year with a culture length of 17 weeks each. Planting dates were 10 September 2003, 14 January 2004 and 19 May 2004. Tomato plants (Lycopersicon esculentum Mill. ‘Espero’), with visible flowers on the 1st, 2nd or 3rd truss, were planted at a density of 3.0, 3.5 or 4.0 plants per m2 in two greenhouse compartments at temperature set points of 21/18/22°C or 24/21/25°C (day/night/ventilation temperature). Results showed that higher plant density, the use of older plants at planting and higher growth temperature increased tomato yields. All growing factors should be adjusted with respect to planting date and light intensity in order to give optimum result. A maximum year-round production of 101 kg m-2 of 1st class tomatoes during 33 harvesting weeks was registered. Based on these results, a yield potential of tomato production using artificial light of 125-140 kg m-2 is realistic. We used our experimental results to develop commercial tomato production in Norway, achieving yields over 100 kg m-2 a year.
Verheul, M.J., Maessen , H.F.R. and Grimstad, S.O. 2012. OPTIMIZING A YEAR-ROUND CULTIVATION SYSTEM OF TOMATO UNDER ARTIFICIAL LIGHT. Acta Hort. (ISHS) 956:389-394
Lycopersicon esculentum, cropping schedule, growth temperature, plant age, plant density, yield potential

Acta Horticulturae