New Zealand Journal of Agricultural Research abstracts
Effects and interactions of phosphorus and sulphur on a mown white
clover/ryegrass sward
1. Herbage dry matter production and balanced nutrition
A. G. SINCLAIR
L. C. SMITH
J. D. MORRISON
K. G. DODDS
AgResearch
Invermay Agricultural Centre
Private Bag 50034
Mosgiel, New Zealand
Abstract The pattern of yield response to phosphorus (P) and
sulphur (S) fertiliser applied in a factorial design involving 5 rates of each
nutrient on a mown white clover/ryegrass sward was studied over 2 years. Large
responses to both P and S occurred with white clover and only small responses
with ryegrass in both years. Over the whole period, in white clover the
response to S was twice the response to P whereas in ryegrass the response to P
was twice the response to S. A bivariate Mitscherlich-related equation was
developed to model the response surface and was found to account for 92.5-95.5%
of the variation in white clover and total DM yields. The fitted equation was
used to identify combinations of P and S fertiliser rates giving rise to
balanced nutrition. Nutrients were defined as being in balance when maximum
possible responses to each applied alone were equal. Once the initial imbalance
between nutrients was eliminated by appropriate application of one nutrient,
the ratio of further S and P required to provide balance at higher levels of
production was relatively constant over application rates, being 0.56:1 S:P for
the full period of the experiment. Economically optimal fertiliser S:P ratios
were calculated from fitted response surfaces and individual nutrient costs.
These ratios were always higher than those which supported balanced nutrition
and this was attributed to the much lower cost of S and its greater agronomic
efficiency on a per kg basis.
Keywords balanced nutrition; bivariate response model; white
clover; economic optimisation; fertiliser; interactions; nutrient balance;
nutrient ratio; phosphorus; response surface; ryegrass; sulphur
New Zealand Journal of Agricultural Research, 1996, Vol. 39: 421-433
0028-8233/96/3903-0421 $2.50/0 (c) The Royal Society of New Zealand
1996
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