The Effect of SO2onLolium perenneL. Grown at Different Levels of Sulphur and Nitrogen Nutrition

The effects of exposure to SO2 (55 η m−3) on the growth and sulphur nutrition of perennial ryegrass (Lolium perenne L.) cv. S23 were examined using a system of specially constructed growth chambers. The plants were grown in soil with two rates of added nitrogen, either with or without added sulphate. They were harvested twice during the exposure period of 85 d. The high rate of added nitrogen gave a four-fold increase in the yield of plants given added sulphate but resulted in sulphur deficiency, with reduced yield and number of tillers, when no sulphate was given. Exposure to SO2 alleviated the effects of deficiency but was without effect on the yield of plants given sulphate. With the low rate of added nitrogen, the yield of plants and the number of tillers were unaffected by the addition of sulphate to the soil or of SO2 to the air. The only indication of possible injury through exposure of these plants to SO2 was a small increase in the proportion of dead leaves at the second harvest. Analysis of the leaves for total S and sulphate-S gave values consistent with sulphur deficiency and its alleviation through exposure to SO2; the contents of 0·045% S and 42 parts 10−6 sulphate-S in deficient plants were raised to 0·102% and 153 parts 10−6 respectively. The organic-S content of the leaves was always increased through exposure to SO2. There was no evidence that exposure to SO2 increased the ‘transpiration coefficient’ for plants having an adequate supply of sulphur from the soil.