Effects of applied nitrogen on grass yield, nitrogen content, tillers and leaves in field swards

TLDR: Effects of three levels of N application and four intervals between harvests on field swards of perennial ryegrass were studied during 6-week periods in summer and spring to develop a larger, positive response to applied N.

Abstract: Effects of three levels of N application and four intervals between harvests on field swards of perennial ryegrass (Lolium perenne L.) were studied during 6-week periods in summer and spring. Ryegrass was compared with tall fescue (Festuca arundinacea Schreb.) in spring and autumn.An increase in the interval between harvests from 1 to 6 weeks allowed a larger, positive response to applied N to develop in respect of dry-matter yield, weight per tiller, and leaf blade and sheath length. Response to N was expressed more in terms of larger leaf blades than in a larger number of tillers. Tall fescue leaf blade size was increased more than that of ryegrass by a period of uninterrupted growth in May.Within 1 week of its application, N had increased the N content of both emerging and dying leaf blades and had increased the width and reduced the weight per unit area of the emerging blades. The positive effect of N on blade width (and on blade length where uninterrupted growth was allowed) and its negative effect on weight per unit area were ‘carried through’ the sward, to be recorded a second time when that generation of blades had become the dying blades.Applied N increased the number of tillers, the rate of emergence of new tillers, the proportion of tiller buds which developed into tillers, and the proportion of relatively young tiller buds which developed.