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Fertiliser - key to profitable and sustainable pasture lands, northern slopes and plains, central Slopes, central west Plains and upper Hunter

R.D. Freebairn

NSW Agriculture, PO Box 116, Coonabarabran NSW 2357

Very few attempts have previously been made to assess sulphur (S), phosphorus (P) or molybdenum (Mo) deficiency in pasture, or the feasibility of using fertiliser across the non-tableland and non-coastal areas of northern NSW. This study, involves nine district agronomists and 36 experiments. It represents over 20 million hectares of grazing country, most of it never previously top-dressed with fertiliser. The study also includes comparing different fertilisers (including organic products), at a similar single standard phosphate rate and evaluating the residual effectiveness of superphosphate (8.6% P,11.5% S) and SF45 (5.5% P,44.6% S).


The study involves a total of 36 experiments, all but one on an annual legume based permanent pasture. Soil types include most of the major soils of the region. Most of the experiments are on pastures never or rarely top-dressed. Two experiments commenced in 1987, but most did not begin until 1989 or 1990. Size of plots varies from trial to trial. They range from 10 m x 10 m to 5 m x 2 m. They are closed to stock between the autumn break and the last spring measurement. They are opened for grazing over summer and uniformly grazed down prior to the beginning of the next autumn break. Experiments are supplied from one to four times during the season.

All but the five Narrabri district trials were replicated three times. These, with the exception of one, were statistically analysed as one trial. All experiments compared a range of products, mostly at a relatively common phosphate rate of about 10 kg/ha. Trials are assessed by random quadrat cuts taken from each plot. All yields have been assessed on a dry matter basis. All trials but one were statistically analysed.

Results and discussion

The average response to approximately 10 kg/ha P and 13 kg/ha S (116 kg/ha superphosphate or similar rate with other fertilisers) was a doubling of plant productivity. All but five of the 36 sites indicated a response to S. There was a P response in all but seven trials, although often the response was small. In 15 trials (42%) the low phosphate but high S fertiliser SF45 (applied at 86 kg/ha or similar rate) yielded almost as much (95%) or better than superphosphate (applied at 116 kg/ha or similar rate). In 23 trials where superphosphate was applied at double the standard rate (232 vs. 116 kg/ha) yield increased a further 28%. Superphosphate was the superior product in almost all low phosphate sites. One trial, on a high phosphate site, after four years, has shown a high residual value following only one application of SF45. Overall there were few responses to Mo (23 g/ha).

The results from this study suggest fertiliser is an economical proposition in an area previously considered too harsh to warrant its use. Other benefits are likely to include increased ground cover, better drought protection, less erosion, improved soil fertility and better soil structure. The benefit of the program is ultimately expected to exceed $200 million per annum.

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