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United States Department of Agriculture

Agricultural Research Service

Title: Greenhouse Environment: Heat and Light

Author
item Frantz, Jonathan

Submitted to: Michigan State University Extension
Publication Type: Popular Publication
Publication Acceptance Date: December 10, 2005
Publication Date: December 10, 2005
Repository URL: http://www.ars.usda.gov/sp2UserFiles/Place/36071000/Publications/Frantz187999_2005_GrnHseEnv.pdf
Citation: Frantz, J. 2005. Greenhouse environment: heat and light. Michigan State University Extension Bulletin.

Interpretive Summary: To maximize productivity, the genetics of a plant must “match” an optimized environment, much like getting the most out of an automobile relies on the car’s make and model and fuel, upkeep, roads, and road conditions. How much light and how warm crops should be grown depend, however, on the genetics and the grower’s goals. In terms of maximising yield, increasing light is an easy, albeit potentially expensive, way to improve yield. To measure light, I would encourage growers to measure light early and often in as many places as they can to get a feel for the amount of light a crop receives with a quantum meter. Remember to measure light at the surface of your crops. Leaf emergence and leaf expansion rates are greatly influenced by temperature so increasing temperature is an indirect way to improve light capture and yield. Ultimately, the largest determinant of yield potential may be what you can afford to grow. The optimum environmental settings will not match the optimum economic cost setting. Growers must walk a fine line between optimised environments for plant productivity and optimized for affordable, profitable crop production.

Technical Abstract: To maximize productivity, the genetics of a plant must “match” an optimized environment. How much light and how warm crops should be grown depend, however, on the genetics and the grower’s goals. For example, lettuce is typically grown in “lower” light than most crops, often between 300 and 400 micromoles m-2 s-1, in order to improve quality. In terms of maximising yield, increasing light is an easy, albeit potentially expensive, way to improve yield. Yield can increase up to and probably beyond 1000 micromoles m-2 s-1 if other environmental parameters are optimised as well. This does not mean that growers should spend a fortune on electric lamps to squeeze a few extra micromoles of light in their greenhouses, but it does mean that growers should not be averse to allowing light (and temperature) to rise in the day for fear of saturating photosynthesis or photobleaching leaves, provided other environmental and management issues are optimised. To measure light, I would encourage growers to measure light early and often in as many places as they can to get a feel for the amount of light a crop receives with a quantum meter. Remember to measure light at the surface of your crops. Leaf emergence and leaf expansion rates are greatly influenced by temperature so increasing temperature is an indirect way to improve light capture. Photosynthesis, and thus yield, is strongly correlated to ground cover and light capture regardless of temperature. Ultimately, the largest determinant of yield potential may be what you can afford to grow. The optimum environmental settings will not match the optimum economic cost setting. The actual setting should be somewhere in the middle. Growers must walk a fine line between rapid growth and reduced quality or higher energy costs.

Last Modified: 12/19/2014
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