Getting the wax out: Micro organisms and non wetting soils by brendan Cant

Dr Margaret Roper: on-farm testing of bacteria that break down wax in soils.

A dash of lime and a few bugs may be the cocktail that quenches the thirst of five million hectares of non-wetting Western and South Australian soils.

CSIRO scientist Margaret Roper has been working on a GRDC-backed project to study the role micro-organisms play in improving soil wettability.

With vast tracts across two of Australia's driest states locking out crucial soil moisture, any increases in water penetration promise huge benefits for graingrowers.

At the CSIRO Plant Industry laboratories at Floreat near Perth, Dr Roper and her technical team, led by Anne McMurdo, have found that soil micro-organisms can break down the waxy residues that cause water to be repelled.

They are now doing on-farm testing of wax-degrading bacteria, such as actinomycetes, in WA's northern wheatbelt at Northampton (coastal plain north of Geraldton).

"These trials may be extended to other graingrowing regions in coming seasons," she said. The selected micro-organisms were those which grew most rapidly on waxes and which produced surfactants to assist in the release of waxes from sand surfaces.

WA's sandy soils are often non-wetting because they contain little or no clay (if present, it can mop up waxes).

Additionally, many native plants produce waxes to avoid desiccation in the hot climate. When this plant matter breaks down it increases the wax content of the soil.

Lime stimulates bacteria

Dr Roper said that adding lime, which reduces soil acidity and creates a better environment for micro-organisms, also could have positive effects on improved soil wettability.

The very finely ground lime used in laboratory trials is more easily absorbed into the soil than coarser and cheaper forms more commonly used by farmers. But Dr Roper recommends farmers establish their own mini-trials using different lime rates and those with high neutralising values.

Evidence from a trial site south of the Stirling Ranges showed that lime stimulated microbial activity and improved soil wettability.

"The challenge now is to transform these promising trial results into practical tools farmers can use to economically improve their soils and maximise returns from cropping and grazing activities," Dr Roper said.

Program 3.4.3 Contact: Dr Margaret Roper 08 9333 6668