FARMERS still face big cost hits despite the Federal Government's offer to leave them out of its emissions trading scheme.

Farm leaders have welcomed the move, but say it's not enough to ease concerns over the impact of the scheme on farmers. They say farmers will still be hit with higher energy, fertiliser and processing costs, and want guarantees on carbon credits for farmers and more support for food processors.

"It's a victory for common sense, but we're reserving final judgment until we see the whole box and dice for farmers," National Farmers' Federation boss David Crombie said.

"There's still a lot of water to go under the bridge.

"We want more detail on alternative policy mechanisms for recognising carbon storage, especially in soils, pastures and crops."

Victorian Farmers Federation president Andrew Broad said the Government had only met one of the farm sector's demands.

"They've moved in the right direction," he said.

"But there's no detail on carbon credits, nothing on helping food processors, dealing with world carbon rules or denying MIS forestry offsets.

"They've only got one out of five, so none of my members are shouting 'yippee' at this stage."

The Government's offer, designed to win Opposition support for the Carbon Pollution Reduction Scheme, has also re-ignited divisions within the Coalition.

The Nationals and some Liberals are still fiercely opposed to any CPRS deal with the Government, but don't appear to have the numbers in the Senate to block any such deal.

"We still have a ridiculous massive tax that exempts part of agriculture and will do nothing to change the world's temperature," Nationals Senate leader Barnaby Joyce said.

Party leader Warren Truss said farmers faced higher electricity, fertiliser, chemical and machinery costs even if they were outside the CPRS. "Virtually all of their inputs will be more expensive," he said.

"The flood of cheap foreign food coming into Australia will also accelerate because it won't be subject to emission taxes.

"More closures and job losses in the Australian food industry are certain."

Prime Minister Kevin Rudd said the offer to permanently exclude agriculture from the CPRS was a "good faith" gesture to help win Coalition support.

Climate Change Minister Penny Wong, who revealed the agriculture concession on the weekend, said the Government accepted that farmers could still help with the emissions-reduction task.

Senator Wong said she would sit down with the Coalition and the NFF to "work through how farmers can contribute to that task", but gave no further details.

Agriculture Minister Tony Burke said the move "gives farmers certainty, and gives it now".

"We will continue to explore opportunities for farmers to gain credits under the scheme," he said.

Agriculture was previously to be left out of the CPRS until at least 2015, with a final decision on inclusion taken in 2013.

Australian Farm Institute executive director Mick Keogh said the Government's vague words meant there was no guarantee of what offsets would be allowed for farmers.

They also left open the possibility of some alternative tax or regulation on agriculture outside the CPRS to achieve lower farm emissions, Mr Keogh said.

"It's a bit soon to be popping the champagne corks at this stage," he said.

The concession on agriculture is not guaranteed to clinch Coalition agreement, with other, more expensive demands for more support for coal, electricity and food processors still under negotiation.

The Government's CPRS legislation passed through the House of Representatives early this week. It will now be debated in the Senate, with a vote due by the end of next week.

The Government wants the CPRS agreed to before a critical United Nations conference on climate change early next month in Copenhagen, Denmark.

But unless the Government can reach a deal with the Coalition on an amended version, it is likely to be defeated.