More than 16 per cent of the European Union's land is affected by soil degradation, but in the accession countries more than a third is affected, according to the first Soil Atlas of Europe, published last week.

This degradation can make agricultural land unsuitable for crop production, necessitating costly processes to restore its fertil ity and putting pressure on the Common Agricultural Policy, the EU's controversial system of farming subsidies.

Arwyn Jones, research scientist at the EU's Joint Research Centre, which produced the atlas, said: "Agriculture depends on healthy soil. But changes in farming, land use and climate are threatening the health of soil in many areas. As the atlas points out, we owe our existence to a thin layer of topsoil and the fact that it rains."

Changing land management practices have impoverished soil throughout Europe. In southern Europe nearly 75 per cent of the soil has an organic matter content - a measure of fertility - so low that it is a cause for concern. But even in England and Wales the percentage of soils classed as low in organic matter rose from 35 to 42 per cent between 1980 and 1995, owing to changes in farming practices.

Farmers have failed to practise some simple measures, such as composting, that could save the soil.

The atlas is the first report to assess all Europe's soil. The study will form the basis of the Soil Framework Directive expected by the end of this year, which is intended to protect Europe's soil from further damage.

The chief threats to soil are identified by the atlas as erosion, degradation from the overuse of fertilisers and pesticides, the loss of organic content, contamination from industry, the loss of biodiversity, salinity, the compacting of soil by agricultural vehicles, landslides and flooding. Action could be taken to reduce the effects of some of these processes, said Mr Jones. "In some cases it's very simple - for example, teaching farmers to plough in line with the land's contours instead of ploughing downhill will reduce the soil loss when it rains."

Farmers should also be encouraged to use more composted organic material, he said. This nourishes the soil without the chemical contamination that comes from using large quantities of artificial fertiliser.

Once soil has been degraded it takes thousands of years to regenerate. "Soil is a non-renewable resource and we need to take action to protect it now," Mr Jones said.