EFFECTS OF GROWTH MEDIA, FERTILIZER RATE AND HOUR AND SEASON OF EXPOSURE ON SENSITIVITY OF 4 SOYBEAN CULTIVARS TO OZONE

The sensitivity of four cultivars of soybean Glycine max (L.) Merr. exposed when 21 days old for 1·5 to 0·60 ppm v/v (1,176 μg/m3) of ozone (O3), was affected by changes in growth media, fertiliser rate, hour and season of exposure. Addition of a soluble fertiliser (6-25-15, N-P-K) at a moderate rate increased plant sensitivity to O3. At a higher fertiliser rate, plants grew as well or better than at moderate rates, but foliar sensitivity to O3 decreased. The relative sensitivity (ranking) of cultivars was often different in different combinations of growth media and fertiliser rate. All cultivars were injured more when exposure started at 0900 and 1130 h than at 1400 h. Plants of all cultivars were larger and more sensitive when exposed on 17 June than on 6 January, 17 March or 31 March. Cultivar sensitivity ranking was affected by the hour and the season of exposure. © 1979.