Gases and Control of the Greenhouse Atmosphere
Measurement and Control of Gas Composition in the Greenhouse Atmosphere
Carbon Dioxide and Oxygen Balance — CO2 and O2
Production with Carbon Sequestration - some large commercial greenhouses have power plants onsite which (1) sell excess electricity to the grid; (2) store and release heat into the greenhouse during cooler nocturnal hours; and, (3) capture Carbon Dioxide (CO2) from the energy production and release it into the greenhouse for increased production.
Capturing Carbon Dioxide from greenhouse boilers is not a new practice.Plants remove Carbon Dioxide with, and produce Oxygen from, their photosynthetic parts; and, in the greenhouse atmosphere the gas balance can reach undesirable proportions for the plants. Plants respire and require adequate Oxygen levels. Soil Oxygen and soil aeration are important considerations for the substrate. Poor drainage and poor soil aeration can lead to stunted plant growth, or worse, an undesirable anaerobic condition. With greenhouse hydroponic production, growers want to assure that the liquid media has sufficient levels of dissolved Oxygen for root growth and greenhouse crop production.
CO2 Fertilization. Air is a mixture of gases, two of which are Oxygen and Carbon Dioxide. Greenhouse managers do not need to replicate the external air composition. It may even be beneficial to add Carbon Dioxide through Carbon Dioxide injection, aka CO2 fertilization or supplemental CO2, above average atmospheric levels. Carbon Dioxide fertilization is a common practice among greenhouse growers of both food crops and ornamentals and can lead to significant yield increases. CO2 depletion is most acute during winter months when ventilation is poor, algae is growing on the glass, and lighting is sufficient or better. Carbon Dioxide released during decomposition of compost can be used to supplement levels of Carbon Dioxide. Organic greenhouse operations should strive to foster gas exchange between composting areas and crop production zones.
Harmful Gases and Air Pollutants
Harmful gases such as propane gas, methane, fluorine, ethylene and various air pollutants can also impair greenhouse production. In the summer a more natural air composition is often realized by opening vents or glass and allowing wind to bring in the outside air into the greenhouse. It is often during the winter in temperate climates that various air pollutants and harmful gases can accumulate to undesirable levels of toxicity where they might stunt plant growth or cause greenhouse crop damage. The harmful gases can accumulate due to: improper ventilation, heating equipment, a hot water boiler's flue gases or other exhaust gases, fumigants, anaerobic soil conditions, excess use of certain fertilizers or growing media, tubing or container leaks, etc. An astute grower wants to ameliorate the situation by detecting, monitoring, and reducing greenhouse air pollutants.