Articles
VENTILATION FOR SUPPLYING BEAN AND TOMATO PLANTS WITH CO2
The importance of air exchange rises with the increasing photosynthetic capacity of the plant canopy.
This also rises while increasingly sealing the greenhouse in order to conserve energy.
To investigate effects of ventilation on plants, a special dewpoint-conditioned chamber for measuring the CO2 gas-exchange of a plant stand (1.60 m2) of beans and tomatoes under natural light conditions was developed.
A ventilating set-up supplies plants in the chamber with a constant air-mass flow rate.
From daily course of photosynthesis the effect of less ventilation could be observed.
The CO2 concentration decreased to below 150 ppm.
Another effect was that the plants were light-saturated earlier than if there had been more ventilation.
A saturating curve whose course varies with plant age is formed when the photosynthetic rate is plotted as a function of ventilation.
The results obtained were utilized for determining the ventilation requirement in greenhouses.
In order to get a 95% production capacity in a bean canopy (LAI=3) as compared with a canopy under natural CO2-conditions, a ventilation rate of 150 m3/m2h should be needed.
If vents remain closed at times of high photosynthetic activity, this plant stand would only produce 12% of the maximum production capacity.