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Effects of Ozone and Sulfur Dioxide on Yield of Red Clover and Timothy

Boyce Thompson Inst. for Plant Res., Cornell Univ., Tower Road, Ithaca, NY 14853-1801.

^* Corresponding author.

ABSTRACT

Although red clover (Trifolium pratense L.) and timothy (Phleum pratense L.) are important crops in the northeast, little is known about their responses to air pollution in the field. A crop of red clover and timothy was exposed to O₃ and SO₂, both alone and in combination, in open-top chambers to evaluate effects on yield. Ozone treatments were charcoal-filtered air, nonfiltered air, and nonfiltered air to which O₃ was added to maintain concentrations 1.5 and 2.0 times ambient. Sulfur dioxide treatments were ambient and three levels of addition that simulated the concentrations and dynamics of exposures near point sources of the pollutant. Yield was based on the total biomass obtained in two harvests each year. Two studies were conducted in consecutive years. Sulfur dioxide had no effect on yield and there were no interactions between the pollutants in either study. In the first year, O₃ produced no effects on timothy but reduced the yield of clover and, consequently, the yield of the combined species. Red clover was less prevalent in the stand in the second year and O₃ had no detectable impact on the yield of clover or on total yield since the stand was dominated by the O₃-resistant timothy. The two studies indicated that effect of O₃ on yield was a function of both the concentration of the pollutant and the relative O₃-sensitivity and prevalence in the stand of the component species.