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Issue Number #34
Issue Date Autumn 2006
Number of Articles Online 1 Articles
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Title Getting Kangaroo Grass to Grow

The following is based on two recently published articles, referenced below.

Restored woodland areas that are comprised mostly of trees have limited habitat values, without the without the floristic diversity of the understorey. However, putting back the understorey often takes more planning, time and knowledge than planting trees, especially when the soil seedbank of native plants has been depleted.

Putting back native grasses first is often a critical step to restoring the understorey in open woodlands and grassland. Tussock grasses and kangaroo grasses in particular have the ability, in the right conditions to compete against exotic weeds, and to provide conditions conducive to the establishment of other understorey species.

Themeda can be introduced to small-sized sites using seedlings, or potted plants, or by transplanting intact sods from existing remnants. For larger sites, it is best to use direct seeding. However seeds that have been 'cleaned' by removing the awn for mechanised direct seeding, have been found to be slower at establishment and less vigorous in growth.

If you have ever picked themeda seeds out of your socks, you may have noticed that it affixes firmly via the backwardly pointing bristles on the seedhead. The seed has a long kinked awn that aids the seed by rotating at the bend when moistened, and buries the seedhead firmly into cracks in the soil (or your socks). The easiest way to direct seed is to spread seed-bearing hay directly onto the site. The hay can be harvested using a sickle or a brush cutter.

Germination of seeds can be enhanced by leaving seeds for a period to 'ripen', by storing in a dry shed for about 9 months. Seeds germinate best when soil surface temperatures are greater than 25 C and when soil moisture is around field capacity.

Burning the seed-bearing hay after scattering can promote germination, reduce shading, and knock back weed competition. Using seed-bearing hay has some limitations, as it is variable in quality with seed densities ranging from 240 to 3000 seeds/kg. It is also bulky and difficult to handle.

Themeda can grow in soils with added fertiliser, although it doesn't enhance growth or survival. However fertilised soil does enhance the growth rate of exotic weeds, and these can impact on the growth of themeda seedlings. Recent trials with organic control methods of weeds in themeda revegetation sites have found that sugar is an effective control agent of annual weeds. It is a good short-term non-chemical and ecologically friendly method of control.

Sugar works because it is one of the fastest ways of reducing soil nitrate levels. Nitrate levels have been found to be high in degraded remnants and very low in undisturbed remnants - tying nitrogen up with sugar applications gives themeda a fighting chance to establish over the weeds.

The rate to use sugar: 0.5kg per square meter of soil, every three months until Themeda is established. This is not necessarily the optimum rate, as further research is needed, you may like to try different rates or cheaper forms of sugar such as molasses.

Sugar reduces soil nutrients by feeding micro-organisms which in turn absorb soil nutrients as they grow, so the weeds are denied access to them. The weeds are starved while the native grass flourishes in low nutrient soil. Once the themeda is established, it suppresses nutrient levels and allows the establishment of other native plants, such as wildflowers.

References

  • Cole I. and Lunt I. (2005) Restoring Kangaroo Grass (Themeda triandra) to grassland and woodland understoreys: a review of establishment requirements and restoration exercises in south-west Australia. Ecological Management and Restoration 6 (1) 28-33
  • Beemster,M. (2006). 'A Sweet End to Weeds'. Australian Landcare March 2006 11-12


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