Ground-breaking studies of erosion

By SIMON COLLINS

A Government scientist says New Zealand is losing soil about 10 times faster than the rest of the world.

Dr Aleksey Sidorchuk of the state-owned Landcare Research has just won a $585,000 Marsden Fund grant to research the mechanics of soil erosion over the next three years.

He said New Zealand was losing between 200 million and 300 million tonnes of soil into the oceans every year - between 1.1 and 1.7 per cent of the world's total soil loss to the oceans.

But New Zealand's land area was only 0.1 per cent of the world's total, making its erosion rate more than 10 times the average.

This was partly because New Zealand was a relatively mountainous country.

But Dr Sidorchuk said erosion in the most slip-prone areas, such as the East Coast, had also got 10 times worse since human beings arrived.

"It was increased by Maori about two times, and by Europeans about five times," he said.

"But those figures are for a rather small area of the East Coast of the North Island, so for the whole of New Zealand I can't say exactly what is the human part."

In contrast to the dramatic slips that scar the East Coast landscape, Dr Sidorchuk said much erosion was invisible - caused by particles of rainwater detaching individual particles of soil on steep slopes.

"You can't see the dispersed type of erosion where soil is going slowly from the slopes, but in two or three generations you lose the fertility of your soil," he said.

"We are trying to look at the roots of the erosion process - the mechanics, how water can detach the particles of soil from the soil surface."

This sort of fundamental research had not been done in the US and Europe.

"So we are very happy that the Marsden Fund has an understanding that fundamental work is very important."

The Marsden Fund is financed by the taxpayer and allocated by the Royal Society to fundamental research projects that will increase human knowledge.

This year it received 801 applications and has made 86 grants totalling $36.7 million, mostly for three years.

Dr Sidorchuk hopes that his work will reveal different rates of erosion in different soil types and under various kinds of vegetation.

Farmers will then be able to use this information to determine stocking levels or to let the most erosion-prone land revert to bush.

"I think farmers in New Zealand know a lot about erosion so they can protect their land. They look at the numbers of sheep on the land, and so on," he said.

New Zealand was rare in that the rules for sustainable land management were well known.

These included retaining woodland cover, not having any spots of bare land, not using steep slopes for pasture but protecting them by scrub or forests, and not having too much stock in one place.

"But maybe they need some support from the Government because the changes can cost money."

Federated Farmers policy director Catherine Petrey said farmers would be wary of any new subsidy.

Subsidies before 1984 had partly caused the erosion problem by encouraging farmers to clear bush on steep land.

"Since all those interventions have been removed and farmers have been farming to meet market forces, you have seen a rapid move away from farming those marginal areas," she said.

But subsidised forestry on the East Coast might be just as damaging, because there was evidence that land was more prone to erosion when pine trees matured at the same time on steep slopes.

"The best people to make decisions as to what is sustainable are those who are seeking to live on the land, because it is fundamental to every farmer you meet that they want to farm for themselves and for future generations."

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