The most effective and cost efficient method of promoting survival of seedlings is to coat the roots in gel just before planting out

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

The tough regimen is set to improve the survival rate of the seedlings when they are planted out. But there is a soft side to the research as well: they have found 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 for Forests NSW plantation improvement group, Dr Dane Thomas.

“This will mean there will be lower infill costs for failed seedlings and a more even plantation development with better eventual wood quality.”

The 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 manifests itself in wind blown trees in the plantation, but begins at seedling stage in the nursery.

These projects examined nursery practices such as initial seedling raising, transplanting, growing out and then planting. They meet with success at every stage.

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

“We instituted a reduced irrigation regime, cycling through normal irrigation and reduced irrigation,” Dane said.

“This prepared the seedlings for a period of reduced rainfall for up to two weeks after planting out.”

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 gel samples brought success, but at a higher financial price. There are three methods that 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 it 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,” Dane 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,” Geoff said.

“The root damage began at the transplanting stage from 512 seedling trays, where the seedlings were pushed out from the bottom.

“There was another opportunity for root damage as the seedlings were pressed into dibble holes in hiko trays that carry 40 seedlings.

“What we were unable to measure was whether or not there was another chance for J-root damage at the final plantation stage.”

They found that 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,” Dane said.

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

“But what we found was 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. It also highlighted germination problems.

“Direct sowing can work with Dunns white gum and spotted gum,” Dane said. “But it will be harder for species like blackbutt, which is a staple in New South Wales, and Gympie messmate, which is common in Queensland.

“In these species it is hard to distinguish between actual seed and just chaff, so there is work to be done now to better separate the seed.”

This article appears in the Winter 2006 edition of Bush Telegraph Magazine.