THE YIELD OF WINTER CEREALS EXPOSED TO SULFUR-DIOXIDE UNDER FIELD CONDITIONS

An open-air fumigation system was used to expose crops of winter barley (Hordeum vulgare L.) and winter wheat (Triticum aestivum L.) to controlled concentrations of sulphur dioxide (SO2) throughout six growing seasons from 1981 to 1987. The fumigation system was designed to achieve uniformity of exposure in the central 9-m-diameter area of a 27-m-diameter fumigation plot. Rates of SO2 release were controlled to follow a predetermined pattern of hourly mean concentrations based upon monitoring data from an ambient site in central England. During each experiment the crops were exposed to four treatments: three plots were fumigated with different levels of SO2 in the range 0.014-0.058-mu-l l-1 and a fourth plot was exposed only to ambient SO2 (0.005-0.011-mu-l l-1). Crop growth and yield were determined on each of these four treatment plots and compared with that on additional untreated companion control plots. During five of the six experiments there were trends for decreased crop dry weight, leaf area and tiller density in the SO2-fumigated plots during the winter and spring, particularly with the highest SO2 treatment. However, these growth depressions disappeared by final harvest during each experiment, except in the medium SO2 plot in 1987. Decreased yield of winter barley was observed with the highest treatment of 0.058-mu-l l-1 SO2 in 1983. This concentration exceeded the current range of annual mean concentrations for urban sites in the U.K. (maximum 0.036-mu-l l-1 SO2). At lower concentrations there were examples of increases in the yield of winter barley (0.023-mu-l l-1 SO2 in 1983) and winter wheat (0.046-mu-l l-1 SO2 in 1984). Within the range of current annual mean concentrations for non-urban sites in the U.K. ( < 0.021-mu-l l-1) there were no significant changes in yield. No consistent pattern was detected in the dose-response of yield to SO2 exposure nor any trend for decreasing yield with increasing SO2 concentration. The responses of growth and yield parameters to SO2 could be related to fungal pathogen occurrence and weather conditions during the seasons.