Barnaby Joyce used his position as drought envoy to justify $2,600 worth of taxpayer-funded charter flights between Melbourne and Horsham to attend a regional show.

The former Nationals leader took the almost 3,00km - or about one hour flight - for a day trip to the regional Victorian town to open the Wimmera Machinery Field Day in March this year.

Figures from the Independent Parliamentary Expenses Authority, document the $2,600 expense as "unscheduled transport" between Melbourne and Horsham as part of Mr Joyce's "parliamentary duties".

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Footage of the event posted on Mr Joyce Facebook page shows him there alongside National MP for Mallee Anne Webster ahead of the May election.

The travel expenses were first revealed by The Guardian on Thursday, with a spokesperson for Mr Joyce confirming he was invited as a guest speaker to open the regional show.

The spokesperson for Mr Joyce cited the tight schedule of his position as drought envoy to justify the expense.

“Due to heavy demands of his scheduling commitments as the drought envoy, a charter flight was deemed the most appropriate means of travel,” he said.

The spokesperson said Horsham was the nearest landing strip.

"Travelling the same distance by car would have taken nearly seven hours non-stop in a round trip."

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Mr Joyce also held meetings with the Australian Dairy Farmers Limited, AUSVeg and Victorian Farmers federation as part of the trip.

"The charter flight was submitted to tender and the cheapest tender was selected," Mr Joyce's spokesperson said.

"This travel by Mr Joyce was only able to be assessed by others because it is approved."

In a Facebook post following the event, Mr Joyce described that he was “on drought envoy duties” speaking with farmers about the “difficulties" they faced in drought conditions.

While connecting flights were also used between Armidale and Melbourne as part of the trip.

Mr Joyce has hit back at critics placing scrutiny on his time as drought envoy for the Morrison government.

He was appointed to the role days after Scott Morrison became prime minister in August last year.

A spokesperson for Mr Joyce said his travel to the regional show was an exception to Mr Joyce's usual travel practices.

"What is not costed in these expenses are his trips as Drought Envoy to the seats of Parkes, Hunter, Maranoa, Wright, Cowper, Calare, Lynne as these trips were made by car," he said.

On Facebook this week Mr Joyce posted a video stating “sections of the national media” had incorrectly stated he had not reported back on his trips during his time in the role.

“Instead of clarifying the veracity of reporting with my office or myself, they perpetuated the myth,” he posted.

He went on to cite a series of correspondence of letters between himself and the Prime Minister.

Last week, Labor asked for Mr Joyce’s final report from his work as a drought envoy, but Drought Minister David Littleproud has told Parliament no such document was ever prepared.

Labor’s agriculture spokesman, Joel Fitzgibbon has demanded an explanation over Mr Joyce’s work in the role.

"The Prime Minister has to explain to the Australian people what he sought to achieve by appointing Barnaby Joyce into this new position of Drought Envoy, Mr Fitzgibbon told Sky News on Tuesday.

"And what return on their investment did taxpayers receive as a result of any activities Barnaby Joyce undertook."