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Disease Detection and Losses

Dispensing and Monitoring Ozone in Open-Top Field Chambers for Plant-Effects Studies. A. S. Heagle, Plant pathologist, Southern Region, Science and Education Administration, U.S. Department of Agriculture, Plant Pathology Department, North Carolina State University, Raleigh, NC 27650; R. B. Philbeck(2), H. H. Rogers(3), and M. B. Letchworth(4). (2)(4)Agricultural engineer, and research assistant, respectively, Southern Region, Science and Education Administration, U.S. Department of Agriculture, Plant Pathology Department, North Carolina State University, Raleigh, NC 27650; (3)Plant physiologist, Southern Region, Science and Education Administration, U.S. Department of Agriculture, Botany Department, North Carolina State University, Raleigh, NC 27650. Phytopathology 69:15-20. Accepted for publication 24 July 1978. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1979. DOI: 10.1094/Phyto-69-15.

The design and function of a system that dispenses and monitors ozone (O₃) in multiple field chambers are reported. The air velocity, O₃ distribution, temperature, light, and plant response in open-top chambers were determined. Once initial dispensing rates were set, the system automatically dispensed and monitored O₃ for set periods each day. The open-top chambers provided a mean air velocity of 2.5 km/hr in the plant growth area. Mean photosynthetic photon flux density (400–700 nm) in the chambers was 88% of ambient. Mean temperature during daylight hours was 0.71 C above ambient. The horizontal variation in O₃ concentration was less than 6, 12, and 14% of the mean, at heights of 30, 120, and 180 cm, respectively. The vertical variation in O₃ concentration was less than 6% of the mean between 30 and 120 cm and less than 19% of the mean between 120 and 180 cm. Studies with field corn (Zea mays) and spinach (Spinacia oleracea) showed that chambers affected plant growth and that plant growth in one portion of a chamber could differ from growth in another portion. When effects of O₃ on injury, growth, or yield were significant, however, there were no interactions between chamber position and the magnitude of these effects.