The conversion of all UK farmland to organic farming would achieve the equivalent carbon savings to taking nearly one million cars off the road, the Soil Association said on Thursday.

Britain's largest organic certification body, issuing results of a research project, said on average organic farming produces 28 per cent higher levels of soil carbon compared with non-organic farming in northern Europe.

"The widespread adoption of organic farming practices in the UK would offset 23 per cent of UK agricultural emissions through soil carbon sequestration alone, more than doubling the UK government's pathetically low target of a 6 to 11 per cent reduction by 2020," the Soil Association said. "A worldwide switch to organic farming could offset 11 per cent of all global greenhouse gas emissions," the organic group added.

Professor of Soils and Global Change at Aberdeen University Pete Smith said organic farming had many practices which increased soil carbon.

He said the main challenge, however, was whether a switch to organic farming would maintain the productivity of the land, adding it would be fairer to compare farming methods on a "per unit of product" basis.

"If you accept there could be lower production, you may need to spread agriculture to other areas of land," he said.