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The Importance of Carbon Dioxide (Co2)
for Healthy Plant Growth
Most of the applied research on greenhouse crops has dealt with effects of environmental conditions on plant growth. Factors such as water, light, temperature and nutrients are more easily controlled for optimum growth. It is now possible to also control and accurately measure Carbon Dioxide concentrations in greenhouse and Controlled Environment Garden (CEG) atmospheres.
Carbon Dioxide (CO2) contributes to plant growth as part of the miracle of nature known as photosynthesis. This enables plants to combine Carbon Dioxide and water with the aid of light energy to form sugar. Some of these sugars are converted into complex compounds that increase dry solid plant substances for continued growth to final maturity. However, when the supply of carbon dioxide is cut off, or reduced, the complex plant cell structure cannot utilize the sun's energy fully and growth or development is curtailed.
Although carbon dioxide is one of three main components which combine to produce the products necessary for plant growth, the amount of carbon dioxide in the air is only 0.03% (250 to 330 parts per million). This compares to 78% nitrogen, 21% oxygen and 0.97% trace gases in normal air. Numerous tests have proven that during the winter months carbon dioxide concentrations inside greenhouses is invariably much lower than in outside air. This same phenomenon has been shown in controlled environment gardens.
CARBON DIOXIDE (CO2)
IMPROVES PLANT GROWTH AND QUALITY
Research has shown that in most cases rate of plant growth under otherwise identical growing conditions is directly related to carbon dioxide concentration.
The amount of carbon dioxide a plant requires to grow may vary from plant to plant, but tests show that most plants will stop growing when the CO2 level decreases below 150 ppm. Even at 220 ppm, a slow-down in plant growth is significantly noticeable.
Colorado State University conducted tests with carnations and other flowers in controlled CO2 atmospheres ranging from 200 to 550 ppm. The higher CO2 concentrations significantly increased the rate of formation of dry plant matter, total flower yield and market value.
CARBON DIOXIDE (CO2)
CUT OPERATING COSTS
WHILE INCREASING PRODUCTION
During the winter months, plants near the middle of greenhouse beds generally do not grow as rapidly as plants at the edge. Tests have shown CO2 concentration lower in the center of greenhouses than near the outer walls. Outside air leaking in through small openings around windows carries enough carbon dioxide to satisfy requirements of plants at the edge of beds. The lack of adequate CO2 lowers the average plant yield quality and market value.
Costly methods of stimulating plant growth, in order to market them at optimum profit, are presently being used. One of these is extra heat (with open vents). This, however, increases operating costs and decreases profit. On the other hand, growers using CO2 are cutting their heating costs as much as 50% while realizing extra profit from increased crop production.
SAMPLE RESULTS FROM CO2 ENRICHMENT STUDIES
BIBB LETTUCE
By adding CO2 to the atmosphere around the plant, a 40% crop increase was achieved. Whereas previous crops averaged 22 heads per basket, lettuce grown in the increased CO2 atmosphere (550 ppm) averaged 16 heads of better quality per basket.
CARNATIONS
CO2 levels to 550 ppm produced an obvious increase in yield (over 30%), but the greatest benefits were earlier flowering (up to 2 weeks) with an increased percentage of dry matter.
ROSES
The addition of controlled carbon dioxide provided a remarkable improvement in blossom quality, number and yield. Plants consistently produced many more flowers with 24 to 30 inch stems. Average yield was increased by 39.7%.
TOMATOES
Work in experimental stations has shown that crop increases of as much as 29% have been obtained by increasing the CO2 concentration. More desirable firmness and more uniform ripening are also observed.
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