New Zealand Journal of Agricultural Research abstracts

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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 S^o applied initially was strongly related (r² = 0.97) to total pasture yield. There were no significant differences in the proportion of S^o 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 S^o 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 S^o 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 S^o 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

PDF file of entire paper: medium quality (749K); (scanned from paper original: notes about this process)

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