A. Mazzanti et al., THE EFFECT OF NITROGEN-FERTILIZATION UPON THE HERBAGE PRODUCTION OF TALL FESCUE SWARDS CONTINUOUSLY GRAZED WITH SHEEP .1. HERBAGE GROWTH DYNAMICS, Grass and forage science, 49(2), 1994, pp. 111-120
The effect of level of nitrogen application upon the dynamics of herba
ge growth in a continuously grazed sward of tal fescue was investigate
d during two successive years. In order to obtain a large range of swa
rd structural conditions, the experiments were carried out with two co
ntrasting cultivars: cv. Clarine and cv. Barcel, and, in Year 2, with
two different sward heights or leaf area indices (LAIs). During each o
f five experimental periods (2-3 weeks), swards received either optimu
m (N2) or deficient (NI) N applications, were maintained at their targ
et LAI, and leaf growth was measured on labelled tillers. With continu
ously defoliated tillers, N shortage had only a small effect on the le
af elongation rate compared with tillers protected by cages. The leaf
production per tiller was only slightly reduced by N shortage, and it
was mainly by the means of a reduction in tiller density that the N de
ficiency resulted in reduced herbage growth per hectare. These results
indicate that, in continuously grazed swards, in contrast with result
s previously found in intermittently defoliated swards, leaf elongatio
n is not the only important component of difference in herbage growth
and that the promotion of tillering rate is an additional pathway for
N response in such management regimes.