The supply of extra carbon dioxide is an often applied method to increase the yield of greenhouse crops. The amount of carbon dioxide in the outside air is, depending on your location, 350 parts per million. This amount is sufficient for plants to grow, however when placing a lot of plants together in a greenhouse, the carbon dioxide levels drop as all plants are using carbon dioxide for photosynthesis. By adding CO2 (CO2 enrichment), it is possible to increase the photosynthesis potential of the crops, especially on sunny days.
CO2 enrichment can be achieved with different methods:
- The supply of pure (liquid CO2)
- Combustion of fossil fuel with Air Heaters
- Combustion of fuels with a central burner, in combination with a heat storage tank
Supplying CO2 may lead to local variations in CO2 concentration throughout the greenhouse because the concentration declines from source to sink. Horizontal, and vertical gradients in environmental conditions are disadvantageous, but inevitable. Most importantly is to prevent a decrease of homogeneity of plant growth an crop production.
For instance with a distribution net, a high CO2 concentration is found near the distribution tubes and a low level close to the ridge, or near the opened ventilation windows. In Dutch greenhouses the distribution lines of CO2 are placed underneath the growing gutter, near the crops. With the natural diffusation of the carbon dioxide to the top of the greenhouse, the plants are sure to benefit from the CO2 enrichment.
The most common method of CO2 enrichment for greenhouse application is the combustion of fossil fuel. The flue gases that are used are not to contain dangerous amounts of injurious componets. Therefore the most used fuel for CO2 enrichment in Dutch greenhouses is natural gas. With the combustion of 1 m3 of natural gas, approximately 1.8 kg CO2 is generated.