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Corn+Soybean Digest

Searching for an Ozone-Tolerant Soybean

A ring of horizontal pipes 70 ft. in diameter seem to hover over a soybean field on the South Farms at the University of Illinois (U of I). The pipes release ozone into the wind as it blows across the soybean plot simulating the higher concentration of ozone that could be a reality for our atmosphere in the year 2050. "In the northern hemisphere, ozone levels in industrial countries are rising at a rate of 1-2% a year and this trend is predicted to continue," said Randall Nelson, one of several USDA-ARS and U of I scientists who have been using this outdoor-air laboratory to study how Illinois crops will fare in the future.

Approximately 1 lb. of ozone is released into each ring per day. This amount exposes the growing soybeans to a level approximately 20% higher than the level found in the air outside of the ring.

The increased ozone levels result in a significant decrease in soybean yield, but not for all soybean varieties.

Nelson said that the most sensitive varieties yielded over 30% less under the elevated ozone concentration compared to normal conditions. The average yield reduction of the 22 varieties tested was 19%. But, a few varieties were quite tolerant of the elevated ozone with yield reductions of approximately 5%.

"We tested varieties that were grown in Illinois more than 50 years ago as well as current varieties," said Nelson. "Ozone-sensitive and ozone-tolerant varieties were found within both groups. There are genetic differences among our current varieties for ozone tolerance, but ozone levels are not sufficiently consistent for soybean breeders to select for ozone tolerance under natural conditions."

As the group continues to test varieties, Nelson believes that even more tolerant lines will be found to exist within the USDA Soybean Germplasm Collection at the University of Illinois.

"The capacity of the SoyFACE [Soybean Free Air Concentration Enrichment] facility permits us to currently evaluate only 22 varieties per year," Nelson said. "We are working to develop procedures that will allow us to more extensively evaluate ozone tolerance. It's important to identify those varieties that are most likely yielding at less than full potential under current conditions and to identify more highly tolerant germplasm for developing future varieties."

Ozone exists in two places. Ozone forms a protective barrier from the sun's ultraviolet rays in the stratosphere about 15 miles above the earth. In recent years, the depletion of this ozone has been making news. The decline increases the ultraviolet radiation that reaches the earth and may increase the incidence of skin cancer and cause other problems.

At the same time that the stratosphere ozone is decreasing, surface ozone is increasing. This ozone is a secondary pollutant. Nitrogen oxides and volatile hydrocarbons are products of burning fuels. With the aid of sunlight, these compounds combine to produce ozone. Because sunlight is critical, ozone pollution is principally a daytime problem in the summer. Because ozone is a secondary pollutant, concentrations can be high in rural areas far removed from the original sources of pollution.

The problems of surface ozone changes are regional, depending in part on proximity to urban and industrial areas. Illinois is likely to be among the soybean-producing areas with the highest ozone exposure. Concentrations for central Illinois have exceeded thresholds for soybean yield reduction in recent years.

The research for this project is funded by the State of Illinois through the Illinois Council on Food and Agriculture Research (C-FAR) Sentinel Program. The entire SoyFACE project coordinator is Steve Long, a Robert Emerson Professor in the Department of Crop Sciences at U of I. Graduate student Kevin Hollis has been instrumental in the day-to-day data collection and assessment. For more information, visit

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