Injury and Yield Responses of Soybean to Chronic Doses of Ozone and Sulfur Dioxide in the Field

Abstract

Beginning 14 days after emergence, Dare soybean plants were covered by chambers and exposed for 6 h per day to ozone (O/sub 3/), sulfur dioxide (SO/sub 2/) and a mixture of these gases. The chamber treatments were carbon filtered air (CF), 5 pphm O/sub 3/ (low O/sub 3/), 10 pphm O/sub 3/ (high O/sub 3/), 10 pphm SO/sub 2/ (SO/sub 2/), and 10 pphm O/sub 3/ + 10 pphm SO/sub 2/ (mix). Plants were also grown outside in ambient air (AA), Injury, growth, and yield of plants were evaluated 43, 92, and 133 days after exposures began. Sulfur dioxide alone or in the mix did not significantly affect these responses. Low O/sub 3/ caused injury and defoliation but did not significantly reduce growth or yield. High O/sub 3/ and the mix caused injury and defoliation and reduced growth and yield. Injury was usually somewhat greater, and yield somewhat less, in the mix than in the high O/sub 3/, but these differences were not statistically significant. The results show that soybean can sustain some ozone injury without loss of yield. The results suggest that, unless acute episodes occur which cause extensive foliar injury, soybean yield will not be reduced in areasmore » with seasonal daily 6-h averages of less than 5 pphm O/sub 3/ or 10 pphm SO/sub 2/. 20 references, 1 figure, 1 table.« less