The 'dump button' in a radio station allows presenters to prevent profanity, defamation, or any other unacceptable content from ever going to air.

Sometimes referred to as the 'seven-second delay', the technology was taken up quickly by commercial radio stations across Australia after the Federal Government legalised talkback radio in 1967.

However, the national broadcaster was cautious in its uptake.

It is understood the ABC first trialled the technology years later in 1976, and within three episodes of its new Talkback Gardener show, the dump button was first used.

So what caused the ABC to freak out and hit the dump button for the first time?

The Country Hour host

In 1976, Allan Humphries had recently moved from Darwin back to Sydney and was hosting the New South Wales Country Hour program.

He recalls the ABC being under a lot of pressure internally to introduce talkback radio technology.

"The ABC was paranoid about allowing people to go on radio live," he said.

"This was [the 1970s], so you had the Vietnam War and the Cold War with the Soviet Union, there was a lot of ABC programs getting broadcast nationally.

"So they really didn't want to give a single person the ability to talk to Australia at any given time and literally say anything."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 55 minutes 14 seconds 55 m 70 Years of ABC Rural ( Tim Lee )

He said the ABC did a lot of work on the seven-second-delay system and started training staff on how to use it.

But it took a while before the broadcaster was willing to put it all into practice.

"The ABC was thinking 'let's find a radio program that's going to be safe'," recalled Mr Humphries.

"And someone said 'let's go to the ABC Rural Department. And how about a talkback gardening program?

"'Surely we're not going to get into any trouble with someone phoning up wanting to know how to prune roses or how to overcome pests and diseases in lemons'."

Can you bonsai a marijuana plant? ( ABC News: Niall Lenihan )

Paired with ABC gardening legend Allan Seale, Mr Humphries was put in charge of the program and the ABC was set.

Unfortunately, there is no recording available within the ABC's archives of the day the dump button was pressed, allegedly for the first time, but according to Mr Humphries, this is how it unfolded.

Allan Humphries: Welcome to Gardening Talkback on the ABC, Brian you've got a question for Allan Seale. Talkback caller Brian: G'day, I want to know if it's possible to bonsai marijuana plants? Allan Seale: (Goes silent and refuses to comment) Allan Humphries: It's an unusual question Brian, what's the background to this? Talkback caller Brian: I've got these marijuana plants in the back of the garden and they're getting a bit too tall and I'm afraid the copper can spot them over the fence. So I want to reduce the height, but not affect the yield.

"By this stage, I was beginning to think my ABC career was going to come to a very abrupt end, so I hit the dump button," Mr Humphries said.

"That was the first time the dump button was hit on the ABC and quite an interesting piece of radio history."

Mr Humphries went on to host a number of programs that were born from the ABC's Rural Department, including a talkback program about hobby farming, initially established to assist city people wanting to have a lifestyle change.

In 2019, the ABC works in 10-second delay.

ABC Rural's Country Hour celebrating 74th birthday

In his book Voice of the Bush: A History of ABC Rural 1945-2015, historian Rob Linn said the ABC Rural Department was at the forefront of new technology and a lot of new programs in the 1970s.

Former NT Country Hour presenter Allan Humphries and current host Matt Brann. ( ABC Rural: Dan Fitzgerald )

"The Rural Department was adapting to the era, producing material on television and radio that both informed the viewing and listening audiences and provided entertainment," he wrote.

"The technology that enabled listeners to telephone the ABC for talkback sessions transformed this type of broadcast."

The department, which kickstarted much-loved programs such as the Country Hour, Landline and Australia All Over, is now part of the wider ABC Regional and Local network.

The Country Hour celebrates its 74th birthday on December 3.