POTENTIAL ASSESSMENT OF GROWTH AND YIELD OF ORGANIC GREENHOUSE TOMATO USING A GEOTHERMAL SYSTEM

Greenhouse CO₂ enrichment is a significant monetary expense but an increasing growing factor under high solar radiation, therefore construction of semi-closed greenhouses is an interesting option. The use of geothermal energy, when allowed by land conditions, may constitute an economical alternative for growers to dehumidify and cool their greenhouses during the sunny days. Our hypothesis was that the Northern production of organic tomatoes grown in ground can be improved both in terms of fruit quality and yield when using a simple air cooling geothermal system. To test this hypothesis, two experimental greenhouse units (225 m²) owned by a private producer were used, tomato plants of cultivar Macarena grafted on Beaufort were used. The control greenhouse was cooled and dehumidified by natural ventilation while the greenhouse prototype used a fan coil geothermal system. The agronomic impacts of a semi-closed greenhouse on growth, yield and plant health were measured during two consecutive growing seasons. From the first year study, increasing CO₂ level by 50% in the semi-closed greenhouse resulted in a yield increase of 24% while CO₂ concentration was 642 ppm in the greenhouse prototype and 486 ppm in the control greenhouse. Validation of these results at a commercial scale is now going on to clearly state on the economic feasibility of a semi-closed greenhouse under American Northern growing conditions and for soil-grown organic crops.