HYDROPONIC GREENHOUSE LETTUCE PRODUCTION IN SUBARCTIC CONDITIONS USING GEOTHERMAL HEAT AND POWER
Geothermal energy has made year round greenhouse lettuce production feasible in the far north at Chena Hot Springs Resort (latitude 65°3N, longitude 146°3W), 96 km outside Fairbanks, Alaska, USA. Lettuce is grown year-round using heat and power generated from geothermal resources. The unique high latitude seasonal conditions with large natural variations in day lengths, light intensities and temperatures pose challenges for greenhouse production. Annual outside temperatures vary from 50°C to +35°C. The shortest day between sunrise and sunset is 3 hours and 33 minutes, and civil twilight extends the day to 24 hours from May 15 through July 27. Continuous adjustments managing the greenhouse environment are therefore necessary to produce lettuce year-round effectively. Commercially available lettuce types and cultivars suitable for long or short days are rotated throughout the year in the nutrient film production system. Long day lettuce selections are usually developed in areas with several hours of definite darkness each day. Growth and development may be acceptable for these long day lettuce types under prolonged twilight and continuous summer light, but not optimal. Short days and limited natural light during the winter half of the year demand supplemental lighting. Metal halide lamps are used to supplement irradiance and extend the day. Various combinations of lighting protocols, timing and qualities are under evaluation to establish the most advantageous and cost-effective growing environment supporting high latitude hydroponic lettuce production.
Karlsson, M.G. and Werner, J.W. (2009). HYDROPONIC GREENHOUSE LETTUCE PRODUCTION IN SUBARCTIC CONDITIONS USING GEOTHERMAL HEAT AND POWER. Acta Hortic. 843, 275-282
Lactuca sativa, alternative energy, nutrient film technique, high latitude, enterprise budget