New Zealand Journal of Agricultural Research abstracts
Effect of high rates of nitrogen fertiliser on perennial ryegrass
growth and morphology in grazed dairy pasture in northern New
Zealand
S. L. HARRIS
E. R. THOM
D. A. CLARK
Dairying Research Corporation
Private Bag 3123
Hamilton, New Zealand
Abstract Nitrogen (N) fertiliser was applied to dairy pastures at rates of 0,200,
or 400 kg N/ha per year on farmlets stocked at 3.24 (LS) or 4.53 (HS) Friesian
cows/ha from June 1993 to June 1995. Annual net herbage accumulation increased
22 and 23% on farmlets LS200 and HS200 respectively, and 37 and 24% on farmlets
LS400 and HS400. Most of the extra herbage was perennial ryegrass. Ryegrass
contents (% total dry matter (DM)) were 71 and 76% on farmlets LS200 and LS400
respectively compared with 61% on farmlet LS0. Ryegrass tiller densities were
also higher on farmlets LS200 and LS400 (6295 and 6673 tillers/ m2 respectively)
than on farmlet LS0 (4072 tillers/ m2). On all farmlets there was a post-flowering
(January-February) increase in tiller density although this increase was enhanced
by N. N application also increased tiller number/plant (3.37, 4.10, and 4.26
tillers/plant on farmlets LS0, LS200, and LS400 respectively). The greater
leaf number and leaf dry weight (DW)/plant on farmlets LS200 and LS400 was
connected to the increased tiller number/plant, although DW/leaf was also significantly
(P < 0.05) greater under N. There was no N effect on leaf sheath or basal
stem, but DW/ tiller was significantly (P < 0.05) greater. Ryegrass plants
formed two types of internodal stolon: I(v) associated with vegetative growth
throughout the year; and I(r) associated with reproductive growth and only
formed during November-January. N had no effect on I(v) formation but 35 and
34% of plants formed I(r) on farmlets LS200 and LS400 respectively compared
with 22% on farmlet LS0. It is suggested the positive effects of N on tiller
number and DW/plant together with the postflowering increase in tillering may
improve persistence of perennial ryegrass in intensively grazed dairy pastures.
Keywords dairy pasture; perennial ryegrass; Lolium perenne; nitrogen fertiliser;
ryegrass content; tiller density; plant morphology; internodal stolon
New Zealand Journal of Agricultural Research, 1996, Vol. 39: 159-169
0028-8233/96/3901-0159 $2.50/0 (c) The Royal Society of New Zealand
1996
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