Influence of the Photochemical Air Pollutant, Ozone, on Grass-Clover Plots Using an Open Air Fumigation System

Fumigation of perennial ryegrass-white clover (Lolirim perenne - Trifolium repens) plots with moderate ozone (03) concentrations caused a decline in the clover content and a reduction in total seasonal yield of the swards. There was no significant interaction between defoliation treatment and 03 fumigation. The ryegrass population benefited from the reduction in competition from the clover in 03-treated plots. These results, obtained from an open air field fumigation system confirm the findings of other experiments which used different grass-legume mixtures grown in open-top chambers or in controlled environments. Fumigation with 03 in summer caused a significant reduction in stolon intercept counts by the end of the growing season. This adverse effect persisted through the winter and into the spring of the following year.