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Penalties of ceasing phosphorus and sulphur applications, to pastures on the north-west slopes of NSW

G.J. Crocker

NSW Agriculture, Agricultural Research Centre, RMB 944, Tamworth NSW 2340

Pastures on the north-western Slopes of NSW have received virtually no fertiliser, especially when compared to the Northern Tablelands. With much of the pasture country previously heavily cropped, and no fertiliser program in place, a lot of this country is now of low fertility. The importance of maintaining a fertiliser program was shown in trials.


Eighteen trials were established between 1987 and 1989 to examine P x S responses from native pastures oversown with sub-clover, and sown pastures of lucerne, phalaris, sub and white clover. Additional treatments were included to look at residual versus yearly applications. Production was measured in the 2nd, 3rd and 4th year after fertiliser was applied each year or in the first year only. After sampling, twice in spring and 3-4 times per year, the remainder of the material was mown off and discarded.

Results and discussion

Although the experiment was designed to measure P x S responses, and over 80% of sites responded to at least one nutrient, the most interesting result was the dramatic drop in pasture quantity and quality with only one application of fertiliser compared to annual applications. Most of the sites were sulphur deficient and gave responses of up to eight fold to S.

Table 1. Average reduction (%) in total DM yield from ceasing fertiliser application for 1, 2 or 3 years compared with yearly applied fertiliser.

Results show that missing one application of fertiliser reduces yearly production by 45% and this increases to 75% after missing three applications. More importantly, by the fourth year, late winter and spring production was reduced by 90%, at a time of feed shortage and high animal requirement. Not only was quantity decreased, but legume content decreased from 78-5%, protein from 20.1-8.6% and plant P content from 0.23-0.19% at one site in June 1990.

If material had been returned, reduction may not have been as large, but the drops in production are still quite alarming. Sites did represent soil types and fertiliser programs that are typical of the area. Country having a long fertiliser history is not as likely to suffer the same drop in production, because of the residual effect and nutrient cycling from the soil organic matter.

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