Tomato yield in a closed greenhouse and comparison with simulated yields in closed and conventional greenhouses

In 2002 tomato was cultivated in a closed venlo-type greenhouse to investigate the influence of cooling with forced air movement along heat-exchangers combined with high CO2 level under summer light conditions on production and quality. Transpiration in the closed greenhouse with forced air movement was, comared to a conventional greenhouse, higher at low light levels (2 instead of 1 kg/m(2)) and lower at high light levels kg/m(2) (4 instead of 5 kg.m(2)). Comparison of the observed yield with crop yields predicted with TOMSIM showed that yield was increased by 22% from 46.2 to 56.2 kg/m(2) compared to a conventional greenhouse with CO2 concentration always above 500 ppm. The higher CO2 concentration in the closed greenhouse (always 1000 ppm) could explain only a 9% yield increase.