On bright days optimum greenhouse production requires the best possible use of the photosynthesis potential. Strategic use of CO2 dosing is an important instrument to achieve this.
Wageningen UR Greenhouse Horticulture has, upon request of the Sweet pepper crop commission, developed a simulation tool for CO2 dosing: the “CO2-viewer”. This programme shows the effects of the dosing strategy chosen by the grower. For instance, with the CO2-viewer one can evaluate whether on a particular day CO2 dosing around midday is better or whether dosing in the morning is to be preferred. The computational results of such an evaluation take all relevant greenhouse building characteristics and climate controller settings into account.
Strategic use of CO2
Clean fuel (natural gas) and good equipment enable growers to increase the CO2 concentration of greenhouse air by using flue gases from boilers and combined heat and power installations. The average maximum dosing capacity amounts to about 200 kg per ha per hour but due to limited storage capacity of het associated heat in the buffer tank, dosing is often restricted. Thus the buffer capacity is determinative of the maximum amount that can be given per day.
This restriction means that CO2 dosing with flue gases cannot simply be switched on in the morning and turned off at sunset. If the maximum dose would be applied in the morning, the CO2 budget for a day would already have been used around midday. This is of course an undesirable situation so a strategy must be applied on the use of the scarcely available CO2. The most common way to comply with such a strategy is a buffer filling curve and some delay on the start of the dosing period. The “CO2-viewer” enables the grower to examine the effects of these strategies on daily photosynthesis. This makes it possible to determine e.g. whether it would on a particular day be better to dose CO2 especially around midday or to do so in the morning, when ventilation outputs are smaller. Shifting CO2 dosing from the morning to the afternoon is meaningful if the benefit of such a ‘shifted kilogramme’ in the afternoon is higher than the loss of benefit in the morning.
Each last kilogramme the same effect
Proper distribution of CO2 over the day requires information about the effect of CO2 dosing on photosynthesis at each moment of the day. This effect is determined by the combination of CO2 concentration increase, greenhouse air temperature and light intensity, and cannot easily be calculated. The new simulation model enables calculation of the effect of each last kg CO2 for each hour of the day, taking into account outdoor conditions, heating and ventilation temperature, and dosing strategy. The available CO2 is optimally used if the value of each last kg of supplied CO2 is about the same throughout the day.