New Zealand Journal of Agricultural Research abstracts
Pasture yield responses to sulphur fertilisers in relation to nutrient ratios
in white clover
J. D. MORTON
A. G. SINCLAIR*
AgResearch
Invermay Agricultural Centre
Private Bag 50034
Mosgiel, New Zealand
L. C. SMITH
AgResearch
Woodlands Agriculture Centre
R D 1
Invercargill, New Zealand
B. S. THORROLD
AgResearch
Ruakura Agriculture Centre
Private Bag 3123
Hamilton, New Zealand
Abstract The agronomic performance of triple superphosphate
(TSP), superphosphate (SSP), 15%(15SS), 22%(22SS), 33%(33SS), 36%(36SS), and
50%(50SS) S superphosphate, TSP/S, di-ammonium phosphate (DAP)/S, RPR (North
Carolina phosphate rock/S), plus no S or P was measured over three years on a
ryegrass/white clover sward near Dipton (mean annual rainfall 1020 mm) in
Central Southland, New Zealand. These fertilisers were applied in November
1994, and in September 1996, SSP, TSP, TSP/S, DAP/S, and RPR/S were re-applied.
There was a large pasture yield response to all treatments compared with no S
or P, but no significant difference in pasture yield between SSP, 33SS, 36SS,
50SS, and DAP/S. Superphosphate was higher yielding than TSP, 15SS, 22SS,
TSP/S, and RPR/S. The rate of So applied initially was strongly
related (r2 = 0.97) to total pasture yield. There were no
significant differences in the proportion of So oxidised 30 months
after application between treatments. In the first two years, clover S/P ratios
were above the optimum range for balanced nutrition (0.7-0.8) for all
fertilisers except 15SS, TSP, TSP/S, DAP/S, and RPR/S. Triple superphosphate,
15SS, and 22SS had clover S/P below the optimum range in the third year. Clover
100 S/N ratios for 33SS, 36SS, and 50SS were in the optimum range (4.8-5.0 for
95-98% RY) for most of the trial and increased into that range for SSP, TSP/S,
DAP/S, and RPR/S by the end of the third year. Most other treatments had clover
S/N ratios below the optimum range. In this Southland environment there was no
pasture yield response from applying extra So over and above an
average of 22 kg sulphate S ha-1 yr-1 (SSP). A lower
average rate of 5 kg sulphate S ha-1 yr-1 plus 15 kg
So ha-1 yr-1 (TSP/S, RPR/S), resulted in a
reduction in pasture yield compared with SSP. To achieve similar pasture yield
to SSP over three years, an initial application of at least 33 kg sulphate S
ha-1 and 77 kg So ha-1 (33SS) was required.
Keywords sulphur fertiliser; superphosphate; pasture yield;
nutrient ratios; triple superphosphate; di-ammonium phosphate; reactive
phosphate rock
New Zealand Journal of Agricultural Research, 1998, Vol. 41: 313-323
0028-8233/98/4103-0313 $7.00/0 (c) The Royal Society of New Zealand
1998
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