The effect of a wide range of nitrogen application rates on the yields from a perennial ryegrass sward with and without white clover
J. agric. Sci, Camb., 74: 227-240
A series of 21 N-fertilizer rates ranging from 0-800 Ib N/acre was applied on a pure perennial rye grass sward and a ryegrass sward with clover. On the pure grass sward the response of dry-matter yield to N rate was almost linear between 0-300 Ib/N acre; it then decreased and became non-significant at 500 Ib/acre. The response of crude-protein yield was linear from 0 to 600-700 Ib N/acre. Inclusion of clover increased yields of dry-matter and crude-protein at low N rates, but decreased responses, so that yields and responses of the grass + clover sward were not significantly different from those of the pure grass sward at > 300 Ib N/acre. Optimum N rate profitable for dry-matter production for both swards was 400-450 Ib/acre and for crude-protein > 600 Ib/acre.