SPECTRAL PROPERTIES OF SELECTED UV-BLOCKING AND UV-TRANSMITTING COVERING MATERIALS WITH APPLICATION FOR PRODUCTION OF HIGH VALUE CROPS IN HIGH TUNNELS

Authors: Krizek, Donald; Clark, Herbert; Mirecki, Roman

Submitted to: Photochemistry and Photobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2005
Publication Date: 8/17/2005
Citation: Krizek, D.T., Clark, H.D., Mirecki, R.M. 2005. Spectral properties of selected UV-blocking and UV-transmitting covering materials with application for production of high value crops in high tunnels. Photochemistry and Photobiology. 81(5):1047-1051.

Interpretive Summary: Various plastic covering materials have been used in the greenhouse production of horticultural crops. There is extensive literature on the chemical and physical properties of many plastics but relatively little has been published on the spectral properties of different greenhouse covering materials. During recent years there has been keen interest in the use of high tunnels for production of tomatoes and other high value crops. While high tunnels lack the sophisticated environmental controls available in most greenhouses, they have the advantage of providing the small farmer with a means of growing produce locally for the fresh market at a lower cost than conventional greenhouses. High tunnels also afford the grower a means of providing modest climate control and of starting crops at least a month earlier in the spring and of extending the growing season by a month in the fall. The objective of the present study was to determine the spectral transmittance of a range of plastic covering materials that might be suitable for covering two high tunnels that were erected at the Beltsville Agricultural Research Center in Beltsville, MD in 2004. The goal was to identify commercially available products that either transmitted or blocked UV wavelengths while at the same time had the characteristics of transmitting high levels of visible light and being stable under ambient solar UV radiation for up to four years. The study focused on evaluating plastic films that either blocked or transmitted UV wavelengths below 380 nm that could be used in high tunnel studies on the effects of UV radiation on comparative growth, yield, and market quality and to provide a tool for integrated pest management (IPM). Comparative measurements were also made on selected glass and plastic materials that have been used in UV exclusion studies to provide investigators with base-line information for selecting suitable filters in future studies.

Technical Abstract: The spectral properties of selected UV-blocking and UV-transmitting covering materials were characterized by means of a UV-VIS spectroradiometer or a UV-VIS spectrometer to provide researchers and growers with guidelines for selecting suitable materials for use in studying the effects of ambient solar UV radiation on the production of tomatoes and other high value crops in high tunnels. A survey was made of a wide range of plastic covering materials to identify commercially available products that had the desired characteristics of transmitting high levels of photosynthetically active radiation and of being stable under ambient solar UV radiation. The study was focused on evaluating films that either blocked or transmitted UV wavelengths below 380 nm to determine comparative growth, yield, and market quality and to provide a tool for integrated pest management (IPM). Based on this survey, two contrasting covering materials of similar thickness (0.152 mm) and durability (4-year polyethylene) were selected and used to cover two high tunnels at Beltsville, MD, one a UV-blocking film and the other a UV-transmitting film. Spectroradiometric measurements were made to determine comparative spectral irradiance in these two high tunnels covered with these materials and under ambient solar UV radiation. Comparative measurements were also made of selected glass and plastic materials that have been used in UV exclusion studies.