Former industry minister Ian Macfarlane has defected from the Liberal Party to join the Nationals.

Reports say the move came after discussions between Mr Macfarlane and senior Nationals, including deputy leader Barnaby Joyce and party leader Warren Truss.

Fairfax Media is reporting that Liberal-aligned LNP member Scott Buchholz will move to the Nationals too.

The surprising move has significant ramifications for Prime Minister Malcolm Turnbull.

Speculators say the defection could see Mr Macfarlane return to the ministry but also take the job of deputy leader under Mr Joyce when Mr Truss retires.

Mr Macfarlane first secured his Queensland lower house seat of Groom as a Liberal in 1998.

Reports say the Nationals expect Mr Truss to announce plans to retire next year.

Given that Mr Joyce holds a NSW seat, insiders suggest a Joyce-Macfarlane ticket would be put together to maintain the balance between NSW and Queensland – the two major Nationals strongholds.

If the move goes ahead, the Nationals' party room would grow to 22 federal MPs.

Mr Macfarlane supported of Mr Turnbull from back as far as the 2009 leadership contest, so his demotion after the most recent leadership spill surprised many in the Coalition.

Mr Truss was asked if he was involved in discussions on the matter before Mr Macfarlane's announcement.

“If this is a plan which you think is orchestrated by Barnaby Joyce then you wouldn't expect me to know about it, would you?” the Deputy Prime Minister said.

“The reality is that we have a strong Coalition arrangement, we work closely together in Queensland as one political party, there are arrangements that are in place about where the rooms that people sit in, in Queensland, and those arrangements have applied since the creation of the LNP.”

“Ian and I have been friends for a long time, we grew up together and we have been friends and I have great respect for his ability.

“He has obviously contributed significantly to the government, so I have a high respect for him but what he wants to do in the future is entirely his decision.”