Five years after her partner was murdered while he was investigating a case of illegal land clearing, a New South Wales woman says she is shattered by an amnesty for those who broke the laws he was trying to enforce.

Key points: NSW Government says there will be no new investigations or prosecutions for historic activity undertaken on properties under the former Native Vegetation Act

NSW Government says there will be no new investigations or prosecutions for historic activity undertaken on properties under the former Native Vegetation Act Partner of murdered environment officer says she is "gutted" by the decision

Partner of murdered environment officer says she is "gutted" by the decision Some farmers still think there is a lack of understanding about biodiversity and land management

Glen Turner was fatally shot at a property near Croppa Creek, in the state's north-west, in 2014, by 79-year-old Ian Turnbull, who was convicted of murder and later died in jail.

Mr Turner, a father of two, had been investigating illegal land clearing on Turnbull's property.

"From the initial anger, I am totally gutted by it," said Alison McKenzie, Mr Turner's partner.

"To me it is a kick in the guts to all the environmental officers, not just my partner Glen, but all the environmental officers who worked so hard to bring those cases to fruition."

The Act was scrapped in 2017 after an independent review of biodiversity legislation.

New laws will resolve historic cases of illegal land clearing. ( Supplied )

New vegetation regime

As of August 1, Minister for Agriculture Adam Marshall said there would be no new investigations or prosecutions for historical activity undertaken on properties under the former Native Vegetation Act.

"I don't want to see farmers who undertook activity, which if they did it today it would be completely legal, prosecuted for activity that they did 10 years ago that might've been illegal at the time," Mr Marshall said.

"We have a new, more flexible framework."

Mr Marshall said any activity that was undertaken by farmers while those old laws were enforced would be assessed under the new regime.

"I was flabbergasted that you could have people being investigated and only starting to be investigated only a month or so ago," he said.

'Hard to get anywhere'

Ms McKenzie said the changes made a mockery of the work done by her partner Glen and others.

Glen Turner was fatally shot on a property north of Moree on July 30, 2014. ( Supplied: Turner family )

"I remember him saying how hard it was to get anywhere with these land clearing cases," she said.

"They just put months and months of work into them only to have the legal teams of the Department say, 'no we are not going to follow that through'."

Even so, about 160 farmers are still being investigated and face prosecution under the old laws, but the Government says those matters will likely be dropped.

"It'll mean that most of the farmers who are currently subject to compliance action will have their cases able to be resolved by applying the new code," Mr Marshall said.

Premier Gladys Berejiklian said she understood Ms McKenzie's anger at the decision.

"I don't begrudge her for a second for feeling the way she does, I can't imagine what she and her family have gone through," Ms Berejiklian said.

"There's no doubt this is an emotional issue for many people."

Changes welcomed by some farmers

Meanwhile, the Northern NSW Ag Alliance said it welcomed the move.

The group said there was a lack of understanding about biodiversity and farm management, and hoped the changes paved the way for new discussions about getting the balance right.

"I think it is a massive coup to have both the Environment Minister and the Ag Minister plus farmers chatting about their problems," spokesman Cameron Rountree said.

"I mean, that has never happened before."

New South Wales Farmers said the pursuit of landholders under the old act was creating unnecessary worry, especially during drought.

NSW Farmers president James Jackson says it's good that landholders won't be pursued. ( ABC New England: Matt Bedford )

"A lot of these people thought they were just doing normal farming practice … [and removing the threat of prosecution] is not a bad thing, it's not a bad thing at all," president James Jackson said.

"I mean, there are too many cockies committing suicide as it is."

But Ms McKenzie said land clearing was a big issue, and that while the majority of farmers did the right thing, some did not.

"There is an element that just think they can do whatever they want," she said.

"And they get away from it and the Government is just enabling them to do that."