Report taken with pinch of salt

Wide-spaced belts of oil mallees will not prevent or recover land salinity, according to a new report by the Department of Agriculture and Food (DAFWA).

Thousands of hectares of Wheatbelt farmland has been turned over to oil mallees, including around 14,000ha of alley plantings, to help fight encroaching salinity and for harvesting and carbon sequestration.

But seven years of research by DAFWA, co-funded by the Rural Industries Research and Development Corporation (RIRDC), has found alleys planted on a 100m spacing will not reduce groundwater levels.

The report’s principal author and DAFWA hydrologist Don Bennett said the research, conducted at Coorow, Goodlands, Tincurrin and Gibson, instead found trees needed to be planted much closer.

“Because oil mallee roots explore the soil outside the planted lines, a typical planting covering 10 per cent of the catchment may reduce recharge by about 30 per cent, whereas at least 70 per cent reduction is required to lower water tables and recover land in most situation, ” he said.

Instead, belts would have to be reduced to 30m in width, making integrating cropping into the system practically impossible.

But Oil Mallee Association general manager Simon Dawkins does not believe the report destroys the case for oil mallees. He said few, if any, farmers would have planted wide belts of oil mallees with the belief that they alone would solve salinity.

“If anyone was thinking the only reason they were planting mallees was to stop salinity, then this information would have an impact on them, but I don’t think this is the only reason that people grow mallees, ” he said.

“A lot of farmers still believe the trees have helped them enormously, including drying out paddocks.

“I never heard people talk about recovering already salty land, nor it being a (sole) solution — it’s just part of a solution.”

Kalannie farmers Ian and Robyn Stanley, who with their sons Clinton and Travis and their wives Morwenna and Carmen run a 25,000ha cropping and sheep enterprise, have planted more than 1.2 million oil mallees in 100m alleys since the early 1990s.

Ian said planting the trees was not just about salinity — they had played a part in managing land degradation caused by water and wind erosion.

“The overall effect on the parts of the farm we planted them on has always been positive, ” he said.

“I’ve got no doubt that we’ve improved the landscape markedly by having trees as part of our system.”

Ian said planting tree belts had helped recover an otherwise unusable tract of land badly affected by wind and water erosion.

“The site isn’t a windblown wasteland anymore, it’s now growing crops, ” he said.

“We can grow 1.5 tonnes of wheat on it now… for that soil type that’s probably about average.

“If you go to that site now, we’ve got trees that are 10m to 15m tall. Despite this report, there is no doubt these trees are using water which would otherwise eventually find its way downstream.

“The fact that we’re growing wheat on that area now and better pastures, means that’s using some of the winter rain which would have also otherwise ended up downstream.”

But Ian admitted aspects of the report could make some growers baulk at the thought of turning land over to alleys.

“I think it would have the effect of putting some people off and perhaps stopping them researching it further, ” he said. “But would I have planted the trees closer together? No.

“The idea of planting them over 30 or 50 per cent of our land would have been foolish, because the impact would have been negative on our ability to farm commercially under a wheat-sheep regime.

“They seem to have focused their report on the one criteria of the area of salt land (recovery) and I think mallees in the landscape are just part of a much bigger toolbox of things we can use.”