Toughening up Eucalypt seedlings

Forests NSW researchers are putting Eucalyptus seedlings through boot camp training to toughen them up before they go out into the big wide earth.

The regimen will improve the survival rate of the seedlings when planted out.

If the seedlings have a good drink of water and a dunking in water retentive gel before they hit the ground, they will be better able to survive a two-week window without significant rain.

'We are trying to bring our plantation survival rate up to 90 per cent or better,' said research scientist with the Forests NSW plantation improvement group, Dr Dane Thomas.

'This will mean lower infill costs for failed seedlings, and a more even plantation development with better eventual wood quality.'

Initial research two years ago set out to grow better seedlings in the nursery to improve survival.

Eighteen months ago the work was extended to specifically examine root quality, which begins at seedling stage in the nursery and manifests itself in wind blown trees in the plantation.

Researchers were aware of anecdotal evidence that toughening up the seedlings might improve their survival chances in the field.

'We reduced irrigation to prepare the seedlings for a period of reduced rainfall for up to two weeks after planting out,' said Dr Thomas.

At the same time the researchers were experimenting with water retention gel treatments in an effort to provide the seedlings with enough moisture to survive up to two weeks without rain after planting.

The water gels brought success, but at a higher price.

Three methods can be used.

One is to soak the seedlings in a gel mixture immediately before planting out, replacing the usual two-minute water soak.

Another was to use the water soak, and to dip the root ball into a gel mixture immediately before it reached the planting hole.

The third method was to place a litre of gel slurry into the planting hole.

'That one was incredibly labour intensive, and so brought planting costs up to $1200 a hectare,' Dr Thomas said.

'The water soak replacement had no increase in labour costs, so at $2 a hectare was the cheapest.

'The best method, at $45 a hectare for gel and labour, was dipping the root ball before planting.'

This $45 for a 90 per cent survival guarantee could be measured against the possibility of replanting, and perhaps missing a season as well.

'That cost is what plantation managers will have to weigh up before they decide whether they will use a gel or take a chance,' Dr Thomas said.

Project officer Geoff Heagney said that during the course of these experiments it was noticed that seedling root quality, measured as the extent of root bend commonly known as J-rooting, was lower than expected and should be improved.

'We found that there was a correlation between nursery practices and J-rooting,' Mr Heagney said.

Gentle handling of the seedlings at the transplanting stage reduced the J-root problem.

This could even be tracked down to individual workers and how they handled the seedlings.

'Gently does it is the answer,' Dr Thomas said.

'This has now been adopted as a nursery practice, which should bring immediate gains in survival rates and reduced J-rooting.

'We found that direct sowing of seedlings into hiko trays, from which they are finally planted out, was the best answer.'

This brings its own problems of increased costs through higher labour demands.

Further information

Contact: Dane Thomas, NSW DPI, on (02) 6656 8800 or danet@sf.nsw.gov.au.