Synergistic effect on field-grown soybeans from combinations of sulfur dioxide and nitrogen dioxide

Gaseous air pollutants are frequently present together in the environment downwind from industrial developments and thus have the potential to cause interactive effects on biological receptors. Accordingly, an investigation was conducted to determine how combinations of the gaseous pollutants, sulfur dioxide (SO2) and nitrogen dioxide (NO2) affect a major crop. Open-air field plots of soybeans (Glycine max L.) were exposed to eight different dose levels of SO2 and NO2, alone and in combination, in the presence of ambient ozone (O3) during 1980 and 1981. The soybean plots were fumigated on 10 occasions in both years of the study during the pod-filling period for an average exposure time during fumigation of approximately 3 h. Mean concentrations during fumigation periods ranged from 0.13 to 0.42 ppm SO2 and 0.06 to 0.40 ppm NO2. Premature senescence, as measured by chlorophyll degradation, was observed in the combined pollutant plots in both years of the experiment. Fumigations with NO2 alone had no effect on seed yields in either year. Exposures with SO2 alone had no effect on yields in 1980 and decreased yields by up to 6% in 1981, possibly as a result of greater concentration peaks. Combinations of SO2 and NO2 had a synergistic effect in both years of the study and resulted in yield decreases ranging from 9 to 25%, depending on pollutant dose.