Damning revelations at the financial services royal commission led National Australia Bank to announce on Tuesday it would no longer charge penalty interest payments for farmers who fall into debt on loans.

NAB chief executive Andrew Thorburn admitted he was ashamed by some of the findings during the inquiry.

"I'm proud of what we do and banks do but sometimes we get it terribly wrong," Mr Thorburn told ABC radio on Wednesday.

NAB, which is Australia's biggest agricultural lender, will also allow producers to use their farm management money to offset against loans.

"We know when people go through drought we don't want to make it worse, not just financially but also emotionally," Mr Thorburn said.

He said the bank was looking at making further policy changes, describing the royal commission as a "burning platform" forcing the bank to face criticism.

"We will be making ongoing changes, there's no question about that."

He said despite making mistakes, NAB's staff overwhelmingly did great things for clients and the inquiry was a "slice" of misconduct.

Australian Associated Press