A CO2 control system for a greenhouse with a high ventilation rate

A Simple CO2 control system was developed for a greenhouse with a high natural or forced ventilation rate. This CO2 control system maintains the difference in CO2 concentration between inside and outside the greenhouse, Delta C, during daytime being small (ca. 5 mu mol mol(-1)), by supplying a variable amount Of CO2 gas with time. Results showed that this system worked satisfactorily, while the CO2 concentration outside the greenhouse varied with time in a range between 350 and 450 mu mol mol(-1) with an average of 380 mu mol mol(-1). In this system, the CO2 supply rate was determined based on the time course of Delta C only, and does not consider any physical or physiological mechanisms Of CO2 balance in the greenhouse. Theoretically, the CO2 Supply rate is equal to the net photosynthetic rate of greenhouse crops (Pn), if both rates of CO2 emitted from the substrate/floor and CO2 exchange between inside and outside the greenhouse are negligibly small. Hence, this CO2 control system will be useful not only for monitoring and increasing the Pn in a greenhouse with a high ventilation rate, but also as a diagnosis tool for monitoring the physiological status of greenhouse crops.