1. The effects of annual applications of 0–12 cwt. per acre of sulphate of ammonia on the herbage levels and yields of sulphate sulphur and total sulphur were investigated in four seeds mixtures 1 year and 4 years after seeding down.

2. There were significant increases in the levels and yields of both forms of sulphur up to the 2 or 4 cwt. per acre level of application in both years. The maximum values occurred at the 6 or 8 cwt. level and the corresponding values at the 12 cwt. per acre rate of application declined in many cases.

3. The cumulative effects of the annual dressings of sulphate of ammonia resulted in substantial increases of approximately 50% in the levels of sulphate sulphur and total sulphur with much smaller increases in the levels of non-sulphate sulphur.

4. Duplicate plots which received 2, 4 and 6 cwt. per acre of sulphate of ammonia also received an additional 2 cwt. per acre immediately after the first cut each year. This splitting of the dressings had no significant effect on the accumulation of sulphur by any seeds mixture. A second cut from the cocksfoot plots in the first year showed the sulphur levels in the plots which received the additional sulphate of ammonia to have increased less than the levels in those which received only the initial dressing. This was explained in terms of the yields of the components.

5. There was a tendency for the rye-grass mixture to contain more sulphate than the other mixtures particularly in the fourth year.

6. The possible significance of the increases found in sulphate levels in the copper-molybdenum metabolism of grazing animals is discussed.