Trees secret weapon in sheep-dip cleanup

Biological methods may soon be used to clean up toxic contaminants around old sheep-dip sites.

Until the early 1990s sheep farmers were required by legislation to dip sheep. Dips were often emptied into creeks or directly on to the soil.

During dipping, residue may have contaminated surrounding areas, and wet sheep standing in a holding paddock would also have contaminated the soil.

HortResearch is carrying out a trial using plants to degrade dieldrin, a persistent organochlorine pollutant found at many dip sites.

HortResearch's portfolio manager Dr Brent Clothier, of Palmerston North, who is in charge of the work, said older sites often contained dieldrin and lindane, another organochloride, as well as arsenic and lead.

Willows and poplars were being planted both to take up water, which restricted the leachate movement away from the area, and to indirectly help to degrade dieldrin.

Clothier said the degradation of dieldrin in the tree root zone was also being studied.

Results indicated that willows stimulated microbiological activity in the soil, which enhanced the degradation of dieldrin.

Over five months, the dieldrin concentration in the root zone of willows was 20 per cent lower than before treatment.

Clothier said poplars and willows were being looked at more and more as multipurpose trees. They could be used as a sponge to soak up dairy effluent, and then fed back to cows.

Studies had shown that eating the tree foliage led to more lamb twins, and the tannins in willows could reduce the amount of methane emitted from livestock.

The advantages of poplars and willows were their quick vigorous growth, their high water use, their ability to coppice and their palatability.

Clothier was recently awarded the J.A. Prescott medal in Melbourne, an annual Australian Science Society award for the outstanding contribution to soil science.

He is the first non-Australian to win it.

In 2000 he was the first non-American to win the American Society for Soil Sciences' Don and Betty Kirkham soil physics award.

- NZPA