3 November 1995

NRA says soil erosion one of main water pollution culprits

SOIL erosion is one of the main causes of herbicide pollution of watercourses from agricultural land, with maize playing a leading role in some areas, says the National Rivers Authority.

Maize, especially on light land, is likely to raise the risk of soil erosion. The area sown to the crop has risen fivefold in the past decade and is set to double in the next, the South Western Regions area environmental manager, Bob Huggins, told a recent meeting of the Arable Research Institutes Association.

"It is a problem. Land is ploughed, worked and sown but when it pours there is nothing to hold the soil and we get massive soil erosion," said Dr Huggins. The soil transported into rivers provides a pathway for herbicides to get into watercourses.

Atrazine from maize appears at highest levels after prolonged rain, when rivers are full. If levels in EC directives were breached it could cost millions to clean up, he said.

Other problems occur. Soil particles are causing sedimentation of gravel beds in many rivers, ruining trout and salmon spawning grounds. And nutrients, especially phosphate, encourage weeds and algae, which can choke watercourses.

Dr Huggins believes the best form of control is to identify and implement better land management practice. "Clearly something has got to be done. Other countries have had the same problems. We should access their research. Using their soil conservation techniques will be low cost, practical and likely to be of the greatest benefit." For such an approach to work a partnership needed to be developed between farmers and the NRA, he said.

"The level of Atrazine in water has not fallen in some areas as we had hoped after its use for non-agricultural applications was banned two years ago."

Maize Growers Association agronomist Simon Draper says: "We have been working with the NRA to reduce the risk of herbicides entering watercourses and we are surprised that levels have not fallen.

"Maximum permitted dose of Atrazine was cut last year to 3 litres/ ha but most maize growers are not using it at all. We are encouraging growers to adopt post-emergence applications of herbicides to minimise levels in the soil.

"Cultivations should be made across slopes to prevent large-scale run off and erosion. And it may be necessary to sow a catch crop to stabilise the soil and drill the maize into that," he says. &#42

MGAs Simon Draper is encouraging growers to adopt post-emergence herbicide applications to minimise soil levels.