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Productivity of Field-Grown Soybeans Exposed to Acid Rain and Sulfur Dioxide Alone and in Combination¹

ABSTRACT

Sulfur dioxide (SO₂)-fumigated and unfumigated field plots of soybeans (Glycine max cv. Wells) were exposed to acid (pH 3.1) or control (pH 5.3) precipitation simulants to determine effects on growth and productivity. The precipitation simulants were applied at approximately 5-day intervals in July and August with a total of 3.4 cm applied in 1977 and 4.5 cm in 1978. Sulfur dioxide fumigations of 4-hour durations were performed 24 times in 1977 and 17 times in 1978, resulting in an average fumigation concentration of 0.79 ppm (89.6 ppm · hour dose) SO₂ the 1st year and 0.19 ppm (13.$ ppm · hour) the 2nd. The acid precipitation simulant produced no statistically significant effect on seed yield in either year and a 4% increase in seed size in 1978. The simulated acid rain may have contributed to the nutritional requirements of soybeans by providing S and N during the critical pod-filling stage. Sulfur dioxide exposure decreased seed yields in both 1977 and 1978 by > 35 and 12%, respectively. Aceelerated senescence, as suggested by increased leaf fall, may be responsible for the decreased yield in the SO₂-exposed plants.

The SO₂ exposure appeared to negate the positive acid rain effect on seed size observed in 1978, when the two treatments were combined. Acid precipitation apparently increased the reduction in seed weight resulting from SO₂ exposure in 1977. Although visible injury was induced by acid rain exposure in a chamber study, only a small percentage (< 1%) of tissue was affected and there was no apparent effect on plant growth. The results of these studies suggest that the possibility for harmful effects on soybean yield from acid precipitation of a magnitude used in this study are minimal; however, soybean yields may be decreased by SO₂ exposures > 13.5 ppm · hour occurring during the growing season.

Key Words: air pollution • acidic deposition • Glycine max

¹ Work performed under the auspices of the U.S. Environmental Protection Agency. This research was performed to fulfill, in part, the requirements of the senior author for the Doctor of Philosophy Degree at the University of Wisconsin-Milwaukee.

² Assistant Ecologist and Ecologist, Ecological Sciences Section, Radiological and Environ. Res. Div., Argonne Natl. Lab., Argonne, IL 60439.

Received for publication February 10, 1981.