Effect of NO/sub 2/ and SO/sub 2/ alone and in combination on the productivity of field-grown soybeans

Investigations of effects on plants from single pollutants are numerous and provide useful determinations of phytoxicity levels; however, pollutants rarely occur alone, and field investigations of pollutant combinations are limited. Combustion processes which generate sulfur dioxide (SO/sub 2/) usually produce a mixture of nitrogen oxides (NO/sub x/), as demonstrated by ambient air monitoring data. In order to determine the effects of pollutant combinations on crop plants, field investigations were conducted in 1980 and 1981 using soybeans (Glycine max L.) exposed to SO/sub 2/ and NO/sub 2/ alone and in combination, in the presence of ambient ozone (O/sub 3/). Open-air field plots of soybeans were fumigated with SO/sub 2/ and NO/sub 2/ through a system of aluminum pipes suspended above the plant canopy, utilizing the ZAPS (Zonal Air Pollution System) design. After being released from the pipe, the pollutant gas concentrations decreased with distance downwind from the pipe as a result of normal turbulent dispersion. In both years of the study, the soybean plots were fumigated on 10 occasions during the pod-filling period for an average exposure time during fumigation of 3 hours. Mean concentrations during fumigation periods ranged from 0.13 to 0.42 ppM of SO/sub 2/ and 0.06 to 0.40more » ppM of NO/sub 2/. Results from both years of the experiment indicated that fumigations with NO/sub 2/ alone had no effect on seed yields. Exposures with SO/sub 2/ alone had no effect on yields in 1980 and decreased yields up to 6% in 1981. Combinations of SO/sub 2/ and NO/sub 2/ had a synergistic effect both years of the study and resulted in yield decreases ranging from 9 to 25%.« less