GROWTH OF LUCERNE (MEDICAGO-SATIVA L) EXPOSED TO SULFUR-DIOXIDE

The effect of exposure to SO2 (0 or 96 .mu.g m-3 SO2) on the growth and S content of lucerne (M. sativa L.) was examined in a period of 135 days during which the plants were harvested 4 times. The lucerne was grown in pots of soil with and without the addition of sulfate and of nitrate. Evidence of S deficiency, including a reduction in the weight, the number and the S content of shoots, occurred in plants grown without added sulfate. Deficiency was alleviated through exposure of plants to SO2. Apart from reducing shoot weight at 1 harvest and generally increasing the concentration of S in the shoots, exposure to SO2 had no significant effect on plants grown with added sulfate. The yield of shoots was greater, and was reduced to a lesser extent with S deficiency, in plants grown with added nitrate than in those dependent on rhizobia. While the transpiration coefficient increased greatly in S-deficient plants, it was reduced where otherwise similarly treated plants were exposed to SO2; this treatment did not alter the coefficient in plants with an adequate supply of S from the soil.