Effects of interval between harvests and application of fertilizer N in spring on the growth of perennial ryegrass in a grass/white clover sward

A perennial ryegrass/white clover sward, which had been grazed for over 2 years, was cut at 1‐, 2‐, 3‐ or 6‐week intervals from 18 April to 28 November 1986. Two rates of fertilizer N application in spring, 0 and 66 kg N ha −1 , were compared. Perennial ryegrass growth was studied in three 6‐week periods, beginning on 18 April, 18 July and 17 October. Clover growth was studied in the same three periods and described by Fisher and Wilman (1995) Grass and Forage Science , 50 , 162–171. Applied N increased the number of ryegrass tillers m −2 , the rate of leaf extension and the weight of new leaf produced tiller −1 and m −2 per week. Increasing the interval between cuts reduced the number of ryegrass tillers m −2 and increased the rate of leaf extension, weight tiller −1 and the weight of new leaf produced tiller −1 week −1 . Increasing the interval between cuts increased the weight of new ryegrass leaf produced m −2 where N had recently been applied, but otherwise had little effect on the weight of new leaf produced m −2 . Applying N favoured the grass in competition with the clover in every respect, whereas increasing the interval between cuts only favoured the grass, compared with clover, where N had recently been applied; where N had not been applied, the ratio of ryegrass tillers to clover growing points in the sward was very little affected by the interval between cuts.