This report is based on annual soil testing over 10 years of 48 dairy paddocks at Vasse Research Centre in the south-west of Western Australia.
The same critical KCl-40 soil test value — about 6.5mg/kg — has been determined for pastures throughout Australia receiving greater than about 560mm annual average rainfall. In this study, soil test values were always above 6.0mg/kg.
Because sulphur mineralised from soil organic matter or dissolved from applied fertiliser can be leached, soil testing for sulphur cannot be used to confidently determine the fertiliser sulphur requirements of high rainfall pastures in the next growing season. As the extent of leaching of sulphur cannot be predicted, the recommendation for these pastures is to always apply fertiliser sulphur after July each year — after the peak of the winter-wet growing season. Tissue testing should be used to assess and improve sulphur management.
The main messages for farmers from the study were:
For intensively grazed ryegrass-dominant pastures
- Apply fertiliser sulphur and nitrogen after each grazing
- Applying 5–7kg S/ha after each grazing supplied sufficient sulphur for ryegrass dry matter production.
For traditional clover-ryegrass pastures which are not top-dressed with fertiliser nitrogen after each grazing but instead rely on clover as the main source of nitrogen for pasture production
- Apply fertiliser sulphur after July each year to supply 25–50kg S/ha