Tasmanian senator Jacqui Lambie has had a heated public dispute with National Farmers' Federation (NFF) president-elect Fiona Simson.

The exchange came hours after the Senate rejected the Coalition's 19 per cent backpacker tax proposal, throwing its support behind Senator Lambie's 10.5 per cent proposal.

The bill was sent back to the House of Representatives and promptly rejected by Coalition MPs, who control the numbers.

It will be reintroduced to the Senate at the Government's preferred 19 per cent rate.

Ms Simson, who was elected NFF president earlier on Thursday, told Senator Lambie she supported the Coalition's 19 per cent proposal and called on her to end uncertainty for farmers.

"[The backpackers] need to get more money in their pocket than they do in New Zealand and Canada and they do that at 19 per cent," she said.

"We need to end the uncertainty and we cannot have this ping-ponging between the House of Representatives and the Senate."

Senator Lambie said she didn't believe the NFF were serving the famers' best interests and called on her "put on her gumboots" and speak with them.

"[The farmers] are already disadvantaged because of the lack of backbone that the NFF have had in the first place by playing lapdogs for the Liberal National Party," she said.

"Please don't come out here and say this sort of stuff because that's absolute rubbish and you know it.

"If you had stood your ground … we wouldn't be in the predicament we are."

Ms Simson will become the NFF's first female president in its 37-year history, after also being the first woman to lead the New South Wales Farmers Association.