Mr Mitchell said while Mr Obama has flagged a protectionist approach, it was unclear what exactly he would actually curb trade.

He said Mr Obama had already promised a review of the NAFTA treaty and was not as positive as his Republican rival about concluding the Doha round.

"If Doha and the WTO negotiations are to succeed, the US will have to make significant changes and concessions with its Farm Bill and the high level of domestic support it provides to its farmers," Mr Mitchell said.

"Yet there are provisions under the current Bill to give more money to farmers which will make it hard for the Doha round to move forward."

Mr Mitchell said even if the current biofuels support program was maintained in America it would continue to have a distortionary impact on commodity prices and food security.

"Farm subsidies are shielding American farmers from the real market signals," Mr Mitchell said.

"What impact that will have in Australia is hard to say because at the moment, the biofuels surge has been positive to date on commodity prices."

Corporate editorial director of US publishing company Farm Progress, Willie Vogt, said the election comes at "an unprecedented time in our country".

Mr Vogt said there was a lot more interest among farmers in this campaign than any others he can remember.

"In this country we'll have the highest voter turnout in the past 30 years with this election," Mr Vogt said.

"This election will be historic in a number of ways and how it plays out in the next four years will be critical at a time when the world economy is soft."

He said there were mixed thoughts among farmers about the effectiveness of the Bush era.

"That depends on what they think of the Iraq War and why we're there. That is really what frames everyone's opinion of Bush these days.

"He (Bush) couldn't even rally Congress around the first draft of the financial bailout."

Mr Vogt said farmers, like all American citizens, have strong views on the campaign.

"A majority are in favour of McCain - but not sure how they'll really vote in the wake of the financial disaster," he said.

"US farmers tend to be more conservative in their presidential politics and liberal in their government programs.

"This means they often vote for the Republican candidate, but get better programs from Democrats."

He said both candidates were "for trade" although Obama could attempt to put some constraints on trade agreements.

But Australian farmers shouldn't expect to see any major changes to the controversial US Farm Bill, which includes monstrous subsidies to the country's farmers, with the new administration.

"There's a long-standing policy on agriculture in the U.S. that would make it difficult for any president to truly effect change on the Farm Bill," Mr Vogt said.

"Even the Bush Administration failed after an effort that included more than 40 national listening sessions."