Farm leaders are at loggerheads with DEFRA over government plans that would require arable farmers to take land out of production and manage it for environmental purposes at a time when food is in short supply.

The deepening dispute centres on the government's determination to press ahead with a replacement for set-aside and compel growers to put as much as 5% of land into environmental management - despite heightened fears over food security.

DEFRA secretary Hilary Benn hopes the change can be successfully negotiated at a European level during CAP "health check" talks this autumn. But NFU chief economist Carmen Suarez said the union had growing concerns about the proposal.

"England is moving in a completely different direction and at a completely different speed to other member states," she told delegates at an NFU Council meeting in Leamington Spa, Warwickshire, on 7 October.

EU member states agreed in principle to abolish obligatory set-aside earlier this year. Although the decision is unlikely to be formally signed off until November, it was announced early to give farmers time to adjust their autumn plantings.

But Mr Benn is keen to "offset the loss of environmental benefits" following the abolition of set-aside, justifying his decision on a report by the Sustainable Farming and Food Delivery Group, chaired by Sir Don Curry.

The NFU has now written to Mr Benn calling for an urgent meeting with the minister in the presence of Sir Don, whose report, it argues, does not make a specific call for arable land to be taken out of production.

NFU president Peter Kendall said the union vehemently disagreed with DEFRA's proposal. Mr Benn's decision to push ahead with the idea as soon as next year was not at all helpful, he added. "It is bonkers and ill thought-out."

DEFRA insists that the proposed requirement would not preclude arable production. Instead, growers would be asked to choose from a range of management practices such as permanent grass buffers, winter stubble, or reduced-input cereal crops.

Farmers would be encouraged to make the most of this land for wildlife through proposed new "top-up" options, which would be available from the 2009/10 cropping year within the Environmental Stewardship scheme.