Using Photosynthesis to Make Supplemental Lighting and Shade Curtain Management Decisions
Dr. John Erwin, University of Minnesota, $20,000, 1 year project
Executive SummaryPlants use light, water and carbon dioxide to synthesize carbohydrates to provide energy for growth. Light levels in greenhouses are commonly increased with supplemental lighting in northern climates or reduced by pulling shading curtains over plants in southern climates. Although significant resources are spent on equipment and energy to alter light levels in greenhouses, we have little data on which to base decisions. Such information is critical when determining whether lights should be turned on or off or whether shade cloth should be opened or closed. We believe growers regularly under-light, over-light or over-shade greenhouse crops which results in reduced growth, crop quality and/or unnecessary energy usage, and decreased profits.
This proposal outlines research that will define the effect of light intensity (irradiance), carbon dioxide and temperature on photosynthesis on seed-propagated and vegetatively-propagated bedding plants species, and potted plant species and integrates that information into a usable form.
Preliminary data shows existing shade cloth systems reduce light too much in North America. In addition, our preliminary data also demonstrates that 1) photosynthesis is maximized on pansy and New Guinea impatiens at 600-800 umol s-1 m-2 (approx. 3000-4000 footcandles), and that 2) the maximum rate of photosynthesis on those species is greatly reduced when plants are exposed to a short 2-3 hour high temperature (95oF; common in greenhouses) exposure.
Our data also suggests that it can take three days for plants to recover from a single-short term high temperature exposure.The benefits of information acquired from research identified in this proposal are many. With more and more growers lighting, and the cost of electricity increasing, these data would directly impact the profitability of a business. For instance, this information will allow growers to answer lighting/shading management questions such as: When should you close a light reduction curtain? Should you close it all the way? Are fans a better investment than light reduction curtains? How much is too much poly fading? When is it, and is it not, better to have an open roof greenhouse? Do you need a light reduction curtain in an open roof greenhouse? When should we turn on lights? When should lights be turned off? Does it make more sense to close a light reduction curtain on cloudy days to save heating costs and turn lights on under blankets? We are sure that results from experiments outlined here will have a significant impact on the industry. We are requesting partial funding for the cost of equipment and software development costs. The single-leafed photosynthesis unit has been purchased and we will pay labor costs and other laboratory equipment costs (computers, etc.). The equipment will be available for other floriculture faculty (see later section) in the U.S. to use. Some have already expressed interest.
For further information contact Dr. John Eriwn at erwin001@umn.edu
