Author
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Frantz, Jonathan |
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Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/19/2011 Publication Date: N/A Citation: N/A Interpretive Summary: When greenhouses are heated in the cooler months, greenhouse managers attempt to minimize air leakage by sealing up gap and holes in the structure. Greenhouses that are sealed well can result in rapid CO2 decrease and negatively influence plant growth. Growers can opt to counteract the low CO2 by supplementing with CO2 during the day. However, it is unknown how the use of supplemental CO2 fits within the framework of sustainable production in greenhouses. In this study, the use of supplemental CO2 was explored in combination with reduced air temperatures to evaluate the feasibility of maintaining or boosting productivity of lettuce compared to a traditionally maintained, well-sealed greenhouse without supplemental CO2. Simulations utilizing Virtual Grower software compared fuel cost, fuel use, and carbon consumed due to heating and CO2 supplementation. It was found, and verified by simple modeling, that in well sealed greenhouses, CO2 quickly decreased to below 300 ppm in traditionally maintained production spaces. Supplemental CO2 boosted growth of lettuce even though temperatures were maintained 3°F lower in that environment compared to the warmer, traditional management scenario. Maintaining a cooler greenhouse but adding CO2 decreased total C consumed by 8% during the 45 day production period and by 7% during the 3 month season that required a well-sealed greenhouse. Additionally, the cost of adding CO2, including tank rental, liquid CO2, and monitoring/control system, was paid for by the fuel savings due to lower temperature set points. These results illustrate that it is possible to save money, heating energy, and carbon from heating when CO2 supplementation is used in certain situations. The use of CO2 enrichment should, therefore, be considered in sustainable systems when its use can counteract the reduced plant growth brought on by lowered temperatures. Technical Abstract: When greenhouses are heated in the cooler months, growers attempt to minimize gaps to reduce air infiltration. Greenhouses that are well sealed can result in CO2 drawdown to the detriment of plant growth. Growers can opt to counteract the low CO2 by supplementing with CO2. However, it is unknown how the use of supplemental CO2 fits within the framework of sustainable controlled agriculture. In this study, the use of supplemental CO2 was explored in combination with reduced temperatures to evaluate the feasibility of maintaining or boosting productivity of lettuce (Latuca sativa L.cv. Grand Rapids) compared to a traditionally maintained, warmer, and well insulated greenhouse without supplemental CO2. Simulations utilizing Virtual Grower software compared fuel cost, fuel use, and carbon (C) consumed due to heating and CO2 supplementation. It was found, and verified by simple modeling, that in a well-sealed commercial greenhouse, CO2 quickly decreased to below 300 ppm. Supplemental CO2 boosted yield and development (total leaf number) of lettuce even though temperatures were maintained 3 deg F lower in elevated CO2 than in the traditional management scenario. Maintaining a cooler greenhouse but adding CO2 decreased total C consumed by 8% during the 45 day production period and by 7% during the 3 month season that required a well-sealed greenhouse. Additionally, the cost of adding CO2, including tank rental, liquid CO2, and CO2 monitoring/control system, was paid for by the fuel savings due to lower temperature set points. These results illustrate that it is possible to save money, heating energy, and carbon from heating when supplemental CO2 is used in certain situations. The use of CO2 enrichment should, therefore, be considered as a tool in sustainable systems when its use can counteract the plant growth and development effects brought on by lowered temperatures. |
