THE USE OF NITROGEN ON GRASS/WHITE‐CLOVER SWARDS*

The problem of combining clover and fertilizer nitrogen was studied in the presence and in the absence of the grazing animal. Results from mown experiments confirmed those of other workers and indicated that the large variation in response of a grass/white‐clover sward was related to level of clover production. Grazing, by recirculating nitrogen, raised the nitrogen status of all swards and increased the response to applied nitrogen. On grazed swards there was generally less clover than on mown swards, but grazing increased the nitrogen transfer from clover to grass. Grazed grass/white‐clover swards responded consistently to applied nitrogen and, at each nitrogen level (up to the 120 lb tested), out‐yielded the grass swards. A single spring nitrogen application to grass/white‐clover swards increased yield early in the season but on occasions reduced mid‐season production. A succession of applications—in early and late spring and summer—gave increased spring growth, stimulated yield in mid‐season and also accentuated the autumn flush. Applied nitrogen decreased clover population but did not impair the ability of the clover that remained to fix nitrogen and transfer it to associated grass. Practical suggestions for the use of clover and fertilizer nitrogen are given.