Tomato Yields from CO2-enrichment in Unventilated and Conventionally Ventilated Greenhouses1

The yield of 2 crops of tomatoes ( Lycopersicon esculentum Mill. cv. Tropic) was determined in CO 2 enriched, unventilated and conventionally ventilated greenhouses. The “ventilated” control house was cooled at 26.5°C with conventional ventilation fans and wetted pads. The “unventilated” houses were cooled at 26.5° by recirculating the greenhouse air through direct-contact heat exchanger pads sprayed with water from evaporative cooling towers and also under severely humid conditions by ventilating at 29.5°. For the first spring crop, the ventilated control house at ambient CO 2 yielded 8.58 kg/plant (0.35 m 2 /plant). Unventilated houses enriched with 650 and 1000 μl CO 2 /liter air had 17 and 48% greater yields than the control. An unventilated, unenriched house suffered a 13% yield decrease. For the second winter crop, the control house yielded 8.48 and 9.70 kg/plant at standard and high nutrient levels, respectively. At the standard nutrient level, unventilated houses yielded 64 and 63% greater than the control at 1000 and 1350 μl CO 2 /liter, respectively. At the high nutrient level, they yielded 35 and 37% greater. A ventilated house enriched to 1000 μl/liter whenever cooling was not required yielded 8 and 10% greater than the control at the standard and high nutrient levels, respectively.