Only in extreme cases will land need to be taken out of production to comply with the soil erosion demands of Catchment Sensitive Farming.

And in most circumstances only minor adjustments to field practices will be required.

That is the reassuring message to arable farmers from Norfolk’s River Wensum catchment partnership, one of four pilot CSF projects which have been running for a year.

Under new EU laws the UK government is obliged to tackle diffuse pollution and return all natural waters to “good ecological status”.

Diffuse pollution in agriculture comes from sediments, fertilisers and pesticides.

“In the first round measures must be in place by 2009 and the first set of targets needs to be achieved by 2015,” says the Environmental Agency’s Jamie Letts.

“Each catchment will have its own set of problems which are being addressed by basic measures like the nitrate vulnerable zones, and by supplementary ones like the agri-environment schemes.”

In the Wensum catchment the problem, somewhat surprisingly given the relatively flat countryside, is from soil erosion. Elsewhere nitrate or pesticide may be more troublesome.

“None of the measures are particularly onerous in the first round.”

But cross-compliance to safeguard single farm payments shows there is already an economic driver at work encouraging farms to make the right moves, he notes.

It takes only 25mm (1in) of rain to dump 2000t of soil into the River Wensum, estimates CSF officer Dougal McNeill.

So it is little wonder that some stretches are now smothered in silt up to 30cm (12in) deep.

Unlike rivers elsewhere in the country which scour well, the Wensum has little fall, says Mr McNeill.

“It means most of the fish are now confined to the deeper pools, usually immediately below mills.”

The 70km chalk stream is an SSSI and an EU area of special conservation.

His role as one of 40 catchment advisory officers is to work closely with a wide range of organisations and people, including farmers, to help restore it to its former glory.

It is home to several species of fish, water voles, otters and white-clawed crayfish, and harbours over 100 different aquatic plants and many insects.

There is little doubt that sediment from fields, which also carries phosphate as a pollutant, is the main and growing problem in the catchment, says Mr McNeill.

The land is mainly a mix of 40% sand, 30% clay and 30% silt.

“It’s a sandy clay loam, which is more prone to erosion.”

EA figures confirm that phosphate levels have risen sharply since the 1970s.

And electric fishing shows that only minnows, which are more tolerant of the silt, are still thriving.

All the other species which need gravel to spawn are declining.

Anglers in particular would like to see the river dredged to clear the silt.

But that would be pointless until the source of the problem is dealt with, he says.

The catchment covers 687sq km and about 800 farms.

“Often the source may be well upstream of where the problem occurs.

So to change water quality we need to get down to individual field scale.

“We have to remember, though, that erosion is a natural process.

So our target is to cut the amount of sediment getting into the river by a third.

The aim is to make the fish population self-sustaining again.”

Computer modelling and consultation with farmers and other interested bodies confirmed that about 25% of the catchment, covering 180 farms, merited special attention.

workshops

Erosion risk maps are being drawn up, and Mr McNeill has begun workshops to show farmers and agronomists how to assess risks that can be managed field by field, according to soil type, cultivations, cropping and slope.

“For example if you are 6ft and your horizon is 40yds or less away you are looking at a slope of greater than 3 where erosion is likely.”

Farmers undertaking the exercise will help themselves meet the cross-compliance demand for a Soil Protection Review, he says.

Depending on the level of risk – low, medium, high or very high – there will be a range of options to be adopted, he says.

A trial on a 400m long sloping field not far from the river is being used to highlight the value of early autumn green cover and the different risks arising from ploughing and minimal cultivations.

“An inch of rain in 36 hours on the porridge left by min-till without any subsoiling poses a particular risk,” says Mr Letts.

Many of the actions farmers can take are included in the ELS and HLS schemes, although some are purely agronomic, notes Mr McNeill.

“We would like them to take a spade to fields to identify signs of compaction.”

Something as simple as breaking up tramlines after harvest is a sensible anti-erosion move for low risk fields.

Where the risk is slightly higher he encourages growers to drill early and leave rough seed-beds to absorb rain more easily.

“We are not asking them to change their whole drilling patterns.

Just concentrate on the riskier fields.”

Use set-aside as a buffer against rivers and ditches, he urges.

A key crop management option involves sugar beet.

“Try to harvest the crop from high-risk fields before autumn rainfall to avoid tractors churning muddy fields.”

Only on the highest-risk fields will it be necessary to apply a long-term fix such as reverting to grassland, he believes.

“And in this catchment that is a tiny area.”

andrew.blake@rbi.co.uk