Managing Native Pastures and Stylo

Summary

The project has shown that the 3P grass component of degraded stylo-augmented native pasture systems can be restored using a combination of burning and spelling even though seed reserves were very low. There was, however, little response until seasonal rainfall events were in the average or above range. At light stocking rates (5.25 ha/head but 3.5 ha/head for year 2000) only a spelling program was needed to rehabilitate the 3P grass yield to natural levels (although only 10% of total DM yield) even though yields of stylo in the pasture reached very high levels.

Burning without spelling was largely ineffective in restoring the 3P grass component although the total grass component improved as a result of higher yields of increaser grasses (unpalatable species whose composition increases as grazing pressure increases). We showed that, at medium stocking rates (3.5 ha/head but 2.3 ha/head for year 2000), burning to reduce stylo competition resulted in a significant improvement in yields of 3P grasses and that there was a further improvement from spelling. There was no improvement in 3P or total grass yield at the heavy stocking rate (1.75 ha/head but 1.2 ha/head for 2000) despite annual spelling for 8 years. Burning effectively reduced the yield of stylo with the major effect being on the seca rather than the verano component.

Yields of stylo in unburnt paddocks reached 8200 kg DM/ha at the end of the 1999 growing season compared with 3600 kg DM/ha in burnt paddocks. If a grass component of 30% to 50% is the aim for stable and productive native grass-stylo systems then this can only be achieved with a burning program to reduce stylo competition regardless of stocking rate. We have shown that sowing introduced improved pastures is also a technically available option for restoring a stable grass/legume balance. Again burning and spelling were necessary to gain and maintain a stable grass/legume balance. It is possible, though, that an ongoing fertiliser program may be necessary to retain the suite of species sown here. On the other hand the proportion of Indian couch increased with time and it eventually would have dominated the grass component without additional fertiliser. The stylo component of commercial pastures sown less than 10 years old increased with time up to 31% whereas those sown 10 to 20 years previously were generally stable over the survey period at approximately 61%. These pastures experienced the usual range of grazing practices for the area.