New Zealand Journal of Agricultural Research abstracts
Balanced and adequate nutrition of phosphorus and sulphur
in pasture
J. D. MORTON
A. G. SINCLAIR*
J. D. MORRISON
L. C. SMITH
K. G. DODDS
AgResearch
Invermay Agricultural Centre
Private Bag 50034
Mosgiel, New Zealand
Abstract Pasture production responses and nutrient
concentrations from 5 rates of phosphorus (P) (0, 10, 20, 40, 80 kg
ha-1) and sulphur (S) (0, 5, 10, 20, 40 kg ha-1) applied
three times in two years were measured on a direct-drilled ryegrass/white
clover pasture in a small plot mowing trial on a site with low fertility
(initial soil Olsen P 5 ug ml-1, soil sulphate-S 3 ug
g-1, soil organic-S 4 ug g-1) over two years. There were
responses in total pasture and clover DM (dry matter) production to P and S in
the second year. The response to S was much greater than to P. A bivariate
Mitscherlich-related equation accounted for 88-96% of the variation in measured
values of clover DM production and ratios of P, S, and nitrogen (N)
concentrations. The fitted equations were used to identify ratios of clover P,
S, and N concentrations that resulted in balanced and adequate nutrition. Two
nutrient elements are in balance when the yield response to one added on its
own in relation to the maximum, equals the possible response to the other added
on its own in relation to the maximum. Balanced nutrition in the second year
occurred at a clover S/P ratio of 0.81-0.93. Using N concentration as an
internal standard, nutrient adequacy is defined as the herbage yield with P and
S in physiological balance relative to the maximum yield with P and S in
physiological balance and expressed as RY [PS]. At 95% RY [PS], adequate
nutrition was achieved at 100 <-> P/N of 7.10 and 100 <-> S/N ratio
of 5.64. Clover S/P ratios derived from economically optimal fertiliser S/P
ratios ranged between 1.03 and 0.82 for P and S fertiliser expenditure of
$50-200 ha-1. Clover S/P and S/N ratios were higher than those
determined in an earlier trial on a more developed site with higher soil
fertility. Overall, the results from the trial reported here confirm that
ratios of nutrient concentrations are useful indicators of balanced and
adequate P and S nutrition for white clover.
Keywords nutrient ratios; adequate nutrition; nutrient
concentrations; balanced nutrition; white clover; phosphorus; sulphur;
nitrogen; pasture
New Zealand Journal of Agricultural Research, 1998, Vol. 41: 487-496
0028-8233/98/4104-0487 $7.00/0 (c) The Royal Society of New Zealand
1998
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