Carbon Dioxide Enrichment in Greenhouses
Carbon Dioxide Enrichment in Greenhouse Crop Production
During particular times of the year in new greenhouses, and especially in double-glazed structures that have reduced air exchange rates, the carbon dioxide levels can easily drop below 340 ppm which has a significant negative effect on the crop. Ventilation during the day can raise the carbon dioxide levels closer to ambient but never back to ambient levels of 340 ppm. Supplementation of carbon dioxide is seen as the only method to overcome this deficiency and increasing the level above 340 ppm is beneficial for most crops. In general, carbon dioxide supplementation is the process of adding more carbon dioxide in the greenhouse, which increases photosynthesis in a plant. Carbon dioxide supplementation is also called carbon dioxide enrichment or carbon dioxide fertilization. Although benefits of high carbon dioxide concentration have long been recognized, advances in new technologies and automation in the greenhouse industry has dramatically increased the need for supplemental carbon dioxide. With the development of improved lighting systems, environmental controls and balanced nutrients, the amount of carbon dioxide is the only limiting factor for maximum growth of plants.
Advantages and Disadvantages
Depending on the crop variety cultivated, an additional supply of carbon dioxide can have several beneficial effects including earlier flowering, higher fruit yields, improved stem strength, and flower size. Supplementing carbon dioxide at an early age reduces the number of days to maturity and plants can be harvested earlier. In flower production, supplemental carbon dioxide increases the number and size of flowers, which increase the sales value because of higher product quality.
When to Supplement with Carbon Dioxide
In general, carbon dioxide enrichment systems should be turned on during sunrise, and turned off several hours before sunset; however, additional carbon dioxide enrichment may be needed if supplemental lighting is used is used at night to insure adequate levels. In general, crop production times from late fall through early spring increases the potential need for carbon dioxide enrichment as it coincides with reduced ventilation rates due to colder outdoor air temperatures.
Recommended Carbon Dioxide Concentrations
The level to which the carbon dioxide concentration should be raised depends on the crop, light intensity, temperature, ventilation, stage of the crop growth and the economics of the crop. For most crops the saturation point will be reached at about 1,000 to 1,300 ppm under ideal circumstances. Carbon dioxide levels exceeding this range have little additional positive effects, and levels exceeding 1,500 ppm may hinder plant growth
Determining the Production Increase in Plant Growth from Carbon Dioxide Supplementation
The effect of carbon dioxide on plant growth and production is somewhat different for different crops, but it is possible to generalize the relative effect of carbon dioxide on production as a carbon dioxide rule of thumb. The rule of thumb has been determined based on the experiments on vegetable crops using a base concentration of 350 ppm, but in principle they are valid for almost all crops. A rule of thumb is obviously not quite precise, but it is simple and generally applicable. This rule of thumb is expressed as follows:
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