Estimates of soybean [Glycine max (L) Merr.] yield losses induced by ambient concentrations of air pollutants are ambiguous, but such estimates are frequently requested and reported. The objectives and justification of this field experiment were to answer the questions: 1) What soybean yield losses are attributable to air pollution and 2) Do open-top chambers properly estimate the impact of air pollution on soybean yields? An experiment including cylindrical open-top field chambers was established in 1973 at Queenstown, Md., on a Mattapex (Typic hapludults) silt loam and repeated in 1974 and 1975 to estimate seed yields of soybean cultivars 'York', 'Dare', 'Cutler', and 'Clark'. Yields were compared for plants growing in chambers (3 m diam and 2,4 m height) equipped to provide carbon-filtered air or unfiltered air, and in no-chamber plots. Treatments were arrayed as four replications of a randomized complete block design with quadrants and cultivars forming a 4 x 4 Latin square as a split-plot for each environment. Concentrations of photochemical oxidants at the experimental site varied by year and within years, but were comparable to concentrations measured near Washington, D.C. During the 3 years, there was no significant cultivar x environment interaction. Mean seed yields from plants grown in nonfiltered air chambers (24.0 quintals/ha) were significantly lower than those grown in either carbon-filtered air chambers (30.0 quintals/ha) or in no-chamber plots (30.2 quintals/ha). The authors could not demonstrate that carbon-filtered air would significantly improve soybean yields over yields of commercially field grown soybeans in this 3-year test. The 20% yield difference between yields of plants grown in carbon-filtered air and in nonfiltered air may be an artifact of the chambers and not a true estimate for air pollution induced soybean yield losses. Soybean seed sizes were significantly increased by drought and by carbon-filtered air.
