SOIL SEDIMENT contamination of watercourses could be up to seven times higher under plough-based systems compared to conservation tillage, according to results from the SOWAP* project.

Sediment concentrations in streams during January were 225mg per litre following conventional ploughing, versus 32mg/litre where conservation tillage was used, results showed.

But by April and June sediment concentrations in both catchments were essentially the same, due to a drop in contamination from the plough-based system, said SOWAP’s Jeremy Biggs.

“The difference is probably the result of heavier rainfall/ saturated soils in winter, leading to more runoff – the disturbed conventionally ploughed soils are more vulnerable to winter erosion than conservation tilled soils.”

Earthworms – which play a key role in improving soil structure – can also be significantly increased under conservation tillage, added UK SOWAP project leader, Ceris Jones.

In one project site in Hungary, the weight of earthworms in conservation tilled plots following winter wheat was five times greater than conventional tilled plots, she said.

Mr Biggs also noted that total winter phosphorous concentrations were slightly higher in streams from conservation tilled catchments than conventionally ploughed streams.

“At present we don’t know why this is. It could be due to cultivation practice or the extent to which biosolids/sewage sludge are applied in the catchments of the streams.”

Phosphorus levels in all catchments were quite low and at levels where only minor biological damage would occur, he added.

Further information on the project can be found at www.sowap.org

*Soil and Water Protection project. Freshwater trials sites were on heavy clay soils in south and east Midlands.