There will be "no stability" for Northern Ireland's farmers if the UK votes to remain part of the EU, former Northern Ireland Secretary Owen Paterson has said.
But responding to the Conservative MP's comments, former National Farmers Union president Sir Peter Kendall warned a vote to leave would create "lots and lots of problems" for cross-border agribusiness.
Sir Peter said claims by the Brexit camp about cheaper food in the event of a Leave vote should be a "wake-up call to every farmer in the room".
However, Mr Paterson said the EU could not promise that farmers here would continue to receive billions in subsidies.
Sir Peter addressed hundreds of people from the farming and agri-food sector at the Eikon Exhibition Centre last night for an UFU debate by Skype, after missing his flight.
Mr Kendall, who is involved with the Farmers for In group, said Northern Ireland and the UK would "find ourselves disadvantaged" in the event of the public voting for Brexit.
"We would have to fight every battle on our own," he added.
However, outspoken EU critic Mr Paterson said the UK would remain an outside player in the EU if it voted to stay. "There is no stability in voting to remain," he added. "They will create this new country and exclude us."
The debate was held at the same site as Northern Ireland's biggest agriculture event, the Balmoral Show, on the former Maze prison site outside Lisburn.
Mr Paterson warned the EU "cannot promise" the UK and Northern Ireland would continue to receive high levels of farm subsidies after 2021.
He told farmers last night that "you will be in power" over decisions if the UK voted to leave the EU.
"We can spend the same amount of money, we would spend more money... we could decide what to do," he added.
"We would tailor that money to our local farming industry and environment."
He said a Brexit would allow farmers here to "tailor a rural policy" for the industry.
Northern Ireland received around £2.2bn from the EU in farm subsidies between 2007 and 2013. But Sir Peter slammed claims by Mr Paterson that a Brexit would give Northern Ireland and the UK the "power" to make their own decisions, saying "the UK Government has been arguing for abolition for payments".
And he said leaving the EU would be "an unravelling of 40 years" of legislation and trade.
One member of the audience asked the panel why the majority of economists had forecast the UK would be worse off outside the EU. Another asked about what would happen to farm subsidies in the event of a Brexit, to which Mr Paterson said the "structure and bones" would be constructed at Stormont.
Speaking about the border, he added that it was "not going to have barriers on it".
But Sir Peter said farming and other industries would be hit by tough border controls in the event of a Brexit.
He also criticised Mr Paterson's claims that the UK would not face harsh tariffs if it voted to leave the EU.
"It is more important to Northern Ireland than the rest of the UK," he claimed.
Mr Paterson said there were "ludicrous scare stories" that other nations would impose harsh tariffs in the event of a Brexit.
"Trade will continue. The idea they are going to spike themselves and jack up tariffs is absolutely ridiculous," he retaliated.
However, speaking generally, Sir Peter said: "I don't like the way these figures (about the EU) are being lied about".
The comments come just a day after Chancellor George Osborne warned that Northern Ireland farmers could face huge cuts to their subsidies from the EU if the public voted for a Brexit on June 23.