Positive effects of carbon dioxide for plant growth
Posted On July 1, 2023
Many articles have been written about the negative effects of carbon dioxide. Sick Building Syndrome, loss of concentration from high levels of carbon dioxide, suffocation in breweries or warehouses, all these things come to mind when we hear the magic phrase carbon dioxide. However, perhaps today, when Venus passes in front of the Sun, we should remember that our original atmosphere consisted of nitrogen and carbon dioxide. Free oxygen is something that isn’t really possible chemically. However, we have it as a result of plant life photosynthesising and converting carbon dioxide to oxygen during daylight hours. This is the original use of solar energy!
Plants require carbon dioxide to grow and why not help them by increasing the level of carbon dioxide? Normally this is undesirable, since carbon dioxide is the original greenhouse gas, as our neighboring planet Venus can attest. But in a genuine, controlled greenhouse environment, there’s no real reason why the carbon dioxide level shouldn’t increase in some way.
In fact, tests have shown that increasing the carbon dioxide level in a greenhouse to 550ppm will speed up plant growth by 30-40%. The natural level of carbon dioxide in the atmosphere is around 450 ppm, having increased from around 250 ppm in the last ice age, so this slight increase may not seem significant at first glance. The point of the matter is that the carbon dioxide level in the average greenhouse with the ventilation system closed will drop sharply due to absorption by the plants and will be around 150 – 200 ppm if nothing is done about it. In summer, the ventilation system will be open, and the circulation of fresh air will increase the level by a useful degree. But what about those long, cold, dark northern winters? Most commercial greenhouses will have lighting and heating systems to encourage plant growth, but you still can’t open up the vents and allow cold outside air into your heated greenhouse without losing all those early crops. The only real solution is to increase the natural level of carbon dioxide in some way. When using it, the general rule of thumb is to increase by about 1000 ppm when the sun is shining (or all the lights are on!) and keep the level around 400 ppm during times of darkness. This will require monitoring as there are many variable factors involved and a simple control unit using an infrared sensor will be able to keep the gas concentration constant at all times.
The rate of consumption varies depending on the crop, light intensity, temperature, stage of crop development, and nutrient level. It is estimated that an average consumption level is between 0.12 and 0.24 kg/h/100 m2 of greenhouse surface. The higher rate reflects typical use for sunny days and a fully developed crop. This equates to approximately 150 liters of carbon dioxide per hour.
There are many processes that naturally and unavoidably produce carbon dioxide: fermentation and combustion are two classic examples. In temperate zones it is necessary to heat a greenhouse (glasshouse is another word for the same thing), and this heating will almost always involve burning fossil fuels, producing carbon dioxide. This leads to the natural need to recirculate the exhaust gases from the heating system to the greenhouse and thus achieve a double advantage for the plants. This will require careful monitoring of the flue gases to ensure that, at most, only trace amounts of carbon monoxide pass into the greenhouse. This is not only bad for the plants but also potentially lethal for the people who work there! Such technology is available with gas monitors that will continuously measure carbon monoxide concentration and have analog outputs that can be used to regulate the burners or operate a switch to shut down the unit in the event of problems. The combination of breweries with greenhouse systems is also a serious matter in some areas. In general, these methods should be approved and really should be worthy of government support. They are not only producing crops, but they are also removing a pollutant that would otherwise be released into the atmosphere.
However, control of added carbon dioxide is essential, as high concentrations of carbon dioxide can cause dizziness or even unconsciousness of personnel. Some plants will require higher levels of nutrients to compensate for some of the changes that occur. In particular, tomatoes and violets are sensitive to high levels of carbon dioxide, hence the need for constant monitoring of the environmental concentration.