New Zealand Journal of Agricultural Research abstracts
Effect of high rates of nitrogen fertiliser on white clover growth, morphology,
and nitrogen fixation activity in grazed dairy pasture in northern New
Zealand
S. L. HARRIS
D. A. CLARK
Dairying Research Corporation
Private Bag 3123
Hamilton, New Zealand
Abstract Nitrogen (N) fertiliser was applied to dairy
pastures at nominal 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.
By June 1995, clover contents on farmlets LS200 and LS400 were 10.6 and 2.2%,
respectively, compared with 16.8% on farmlet LS0. Most loss of clover on
farmlets LS200 and LS400 occurred during the first 6 months of the trial when
slow early-spring growth of clover combined with high N responses put clover at
a competitive disadvantage. N had a smaller effect on clover content under the
high stocking rate because of improved utilisation of N-boosted pasture. By
June 1995, there was little difference in clover content between farmlets HS0
(15.4%) and HS200 (14.9) although clover content was lower on farmlet HS400 at
6.8%. The decrease in clover content under N fertiliser on the low-stocked
farmlets was confirmed by the decrease in clover plant density and stolon
biomass. N fixation activity was consistently higher under no N fertiliser than
on either of the low-stocked farmlets which received N. Application of 400 kg
N/ha per year had a significant (P < 0.05) effect on clover plant
morphology but plants on farmlet LS200 were no different to those on farmlet
LS0. Plants on farmlet LS400 had lower stolon length and stolon dry weight
(DW), developed fewer axillary buds, and therefore had fewer stolons. Although
total leaf DW and number of leaves/plant were lower on farmlet LS400, values
for number of leaves/stolon and individual leaf DW were not significantly
different. There were no significant differences between populations in either
root number/plant or root DW/plant.
Keywords dairy pasture; white clover; Trifolium repens
L.; nitrogen fertiliser; clover content; growing point density; plant
morphology; stolon; axillary bud
New Zealand Journal of Agricultural Research, 1996, Vol. 39: 149-158
0028-8233/96/3901-0149 $2.50/0 (c) The Royal Society of New Zealand
1996
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