Response of Soybeans to Chronic Doses of Ozone Applied as Constant or Proportional Additions to Ambient Air

Abstract

Field-grown soybenas (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 proportion 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 .mu.l/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.