Prime Minister Scott Morrison has defended a decision to send his predecessor Malcolm Turnbull to a global oceans conference in Bali next week, after special drought envoy Barnaby Joyce lashed the decision as making ‘no sense’.

Mr Morrison said the decision was made many weeks ago, and argued Mr Turnbull’s “excellent relationship” with Indonesian leader Joko Widodo would make him a fine ambassador for the event.

“It’s not uncommon for former prime ministers to represent their country,” Mr Morrison told Adelaide radio station FiveAA.

Mr Morrison said he knew some people were “disappointed” or “angry” about the decision, but said the “national interest” had to come first.

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The questions were prompted by an extraordinary criticism from former Nationals leader Barnaby Joyce, now the prime minister’s “special envoy” on the government’s response to drought.

Mr Joyce told 2GB the Bali trip was a “problem”.

“There should have been a bit more thought put into this. I don't think it was the right move," he said.

Mr Joyce blamed Mr Turnbull for the government’s shock loss in Wentworth, which robbed the Morrison of its one-seat majority in the House of Representatives and delivered a minority government.

“If it cost the majority in parliament, I’d say there’s a serious question to be asked, are you going to be rewarded with a position in going to Bali?”

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“It makes no sense to me. I am very disappointed Malcolm didn't help out, and it's really a shame for Malcolm because it just spoils his own legacy.”

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“He will be remembered for this. He will be remembered for leaving the Parliament and not helping out his own party, that he was the leader of, win his seat.”

The oceans conference begins on October 29.