Effects of ambient levels of air pollution on grass swards subjected to different defoliation regimes

The urgent need to evaluate effects of air quality on plant growth in the field is discussed in relation to the difficulties which field-based studies pose in the interpretation of data. An initial study is described which aimed to overcome some of these difficulties and the data are discussed within the remaining limitations. The productivity of pure swards of Lolium perenne L. and Dactylis glomerata L., subjected to defoliation at different times of the year, was studied at field sites with different levels of sulphur dioxide pollution, for a period of three years. The field sites and propagation methods were chosen so as to minimise differences in environmental conditions other than the degree of air pollution. At the most polluted site, both species showed signs of visible injury during the first winter and subsequently produced much lower yields than grasses at the other sites. The effects of cutting regimes on the growth of D. glomerata and L. perenne differed for the three years of the study. However, there was a tendency for lower yields with frequent defoliation (every 6.5 weeks), as opposed to the less regular defoliation regimes. It was concluded that air pollution was at least partially responsible for the yield reductions recorded. However, it was considered that sulphur dioxide was not the only pollutant responsible.