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Response of Soybeans to Chronic Doses of Ozone Applied as Constant or Proportional Additions to Ambient Air. Allen S. Heagle, Plant pathologist, U.S. Department of Agriculture-Agricultural Research Service, Department of Plant Pathology, North Carolina State University, Raleigh 27695; Virginia M. Lesser(2), John O. Rawlings(3), Walter W. Heck(4), and Robert B. Philbeck(5). (2)Research technician, Department of Plant Pathology, North Carolina State University, Raleigh 27695; (3)Professor of statistics, Department of Statistics, North Carolina State University, Raleigh 27695; (4)Plant physiologist, USDA-ARS, Department of Botany, North Carolina State University, Raleigh 27695; (5)Agricultural engineer, USDA-ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27695. Phytopathology 76:51-56. Accepted for publication 29 July 1985. 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, 1986. DOI: 10.1094/Phyto-76-51.

Field-grown soybeans (Glycine max (L.) Merrill ‘Davis') were exposed to chronic doses of ozone (O₃) for 7 hr/day from shortly after emergence until maturity. The O₃ doses were applied by supplementing the O₃ present in unfiltered air in open-top field chambers. Ozone was added in constant or in variable amounts which were proportional to ambient O₃ concentrations. The two methods of addition gave similar seasonal mean O₃ concentrations but there were greater fluctuations and higher peak concentrations with the proportional method than with the constant-addition method. Regression of yield response on O₃ concentrations showed no significant differences between types of additions and was similar to that obtained for Davis soybean in 1981. Calculated yield reductions at the ambient O₃ concentration of 0.050 ppm (1 ppm v/v = 1 μl/L) by using the Weibull model for the two methods of O₃ addition combined was 10%, assuming 0.025 ppm as the natural O₃ concentration.