Sulfur dioxide effects on yield and seed quality in field-grown soybeans.

Field plots of soybeans were periodically exposed to elevated levels of sulfur dioxide with an open-air fumigation system which minimized disruption of the normal crop environment. Although visible injury was observed in only two plots, yield at harvest was reduced in every fumigated plot compared to nearby unfumigated control plots. These yield decreases ranged from 5% to 48% and were somewhat greater than might have been expected from previous studies. Yield reductions seemed to be due to decreases in both the mean weight per seed and the number of seeds per plant. Seed quality was affected less than seed yield, although at the higher exposure levels protein content decreased slightly and concentrations of some mineral elements were altered.