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Effects of Daily Ozone Exposure Duration and Concentration Fluctuation on Yield of Tobacco. Allen S. Heagle, Plant pathologist, USDA-ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27650; W. W. Heck(2), V. M. Lesser(3), and J. O. Rawlings(4). (2)Plant physiologist, USDA-ARS, Department of Botany, North Carolina State University, Raleigh 27650; (3)Statistician, Department of Statistics, North Carolina State University, Raleigh 27650; (4)Professor of statistics, Department of Statistics, North Carolina State University, Raleigh 27650. Phytopathology 77:856-862. Accepted for publication 3 December 1986. 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, 1987. DOI: 10.1094/Phyto-77-856.

Flue-cured tobacco (Nicotiana tabacum ‘McNair 944’) was exposed to chronic doses of ozone (O3) in open-top field chambers to determine the influence of frequency and magnitude of peak O3 concentrations and daily exposure duration on tobacco yield response. The treatments were established by adding O3 in amounts that were proportional to ambient O3 concentrations or in constant amounts. The frequency of occurrence and level of peak O3 concentrations were greater for each proportional-addition treatment than for the corresponding constant-addition treatments. However, the seasonal mean O3 concentrations were nearly identical, and the yield response to O3 was similar for both types of O3 addition. Yield in plots receiving proportional addition of O3 for 12 hr/day (1000 to 2200 hours EDT) was 10% less (three treatment levels combined) than in those receiving proportional addition for 7 hr/day (1000 to 1700 hours EDT). If other important crop species have a similar response to O3 late in the afternoon, previous national crop loss estimates based on seasonal 7-hr/day O3 exposures may be low.

Additional keywords: air pollution, yield effects.