Chapter 7

Carbon Dioxide in Greenhouses

(draft book excerpts)

In a greenhouse filled with plants, carbon dioxide concentration will closely follow ambient outside concentrations during the day as long as ventilation is needed. Carbon dioxide concentrations rise during the dark period because plants are not using carbon dioxide for photosynthesis and respiration. In the greenhouse, there may be times when carbon dioxide levels fall below outdoor levels and limit plant growth. Carbon dioxide levels can fall quite low in airtight greenhouses when vents are kept closed for extended periods during the winter months. With little air exchange to the outside on cold bright days, photosynthetic rates can be high and deplete indoor carbon dioxide levels below outdoor ambient levels, thus limiting photosynthetic rates. In a tightly closed greenhouse with plants, the carbon dioxide concentration can drop to 150 to 200 ppm; normal ambient level of carbon dioxide is approximately 350 ppm. This concentration is at or close to the carbon dioxide compensation point where plant growth is adversely affected. An option in counteracting potential carbon dioxide drawdown in greenhouses is to supply supplemental carbon dioxide. Many studies have shown that carbon dioxide concentrations (e.g., 800 to 1,000 ppm) well above ambient levels can benefit plant growth. Typically, a three- to four-fold increase in carbon dioxide concentration yields a 10 to 25 percent increase in plant growth. Supplemental carbon dioxide is often referred to as “CO2 fertilization” or “CO2 enrichment.”

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Within This Chapter: Carbon Dioxide in Greenhouses

  • Introduction to Carbon Dioxide in Greenhouses
  • Carbon Dioxide and Plants
  • Carbon Dioxide Concentration
  • Carbon Dioxide Depletion
  • Carbon Dioxide Effect on Plant Growth
  • Carbon Dioxide and Light
  • Carbon Dioxide and Nutrition
  • Carbon Dioxide Supplementation in Greenhouses
  • When to Supplement with Carbon Dioxide
  • Methods of Carbon Dioxide Supplementation
  • Ventilation
  • Carbon Dioxide Supplementation via Combustion
  • Natural Gas Carbon Dioxide Generators
  • Boiler Stack Carbon Dioxide Recovery Systems
  • Liquid Carbon Dioxide Supplementation
  • Control of Carbon Dioxide Levels in the Greenhouse
  • Recommended Greenhouse Carbon Dioxide Concentrations
  • Distribution of Carbon Dioxide in the Greenhouse
  • References