Physical principles of row covers and grow tubes with application to small fruit crops

Abstract

Protected cultivation has been used to modify the microclimate to advance maturity, increase yields, and expand areas of production for many horticultural crops. Ancillary benefits of protected cultivation can include reduced numbers of pests and lower disease pressure. This discussion will limit the term “protected cultivation” to row covers, low tunnels, and individual plant shelters (“grow tubes”), addressing their applications in the production of small fruit. The foremost biological response of crops grown under protected cultivation is an increase in growth rate, induced primarily by elevated soil and air temperatures within the shelter and around the plant. The protected environment often has lower vapor pressure deficits between crop and atmosphere, resulting in less plant stress. Although many reports detail the biological responses of crops grown under protected cultivation, few include measurements of environmental variables within plant shelters. Understanding the physical principles governing microclimate modification by row covers and grow tubes is essential for effective use of these materials. The optical properties of a covering material and its porosity largely determine the cover’s influence on plant growth and development. Optical properties and cover porosity will be discussed in terms of heat transfer between the crop and its environment. The benefits of row covers and grow tubes have been most dramatic in cool or maritime climates where their use can extend the growing season or make possible the production of warm-season crops. Technological advancements in plasticulture could lead to ‘prescription’ plastics, where covers with specific optical properties and ventilation characteristics are made available for site- and crop-specific applications, particularly small fruits. © 2001 by The Haworth Press, Inc. All rights reserved.