The son of Ian Turnbull, the octogenarian farmer who gunned down a NSW environment officer investigating him for illegal land clearing, has been ordered to carry out repairs worth $4.5 million to one of the family properties.

A Land and Environment Court judgment has found Grant Wesley Turnbull was responsible for illegally clearing 508ha of land over an 18-month period.

It was these actions that led to his father committing murder.

Justice Malcolm Craig found Turnbull had not stopped his father from clearing land that was the subject of court orders on his property, Colorado, at Croppa Creek, about 60km north-east of Moree.

"The explanation for that latter work occurring and not being disclosed was that he had failed to provide his father with the appropriate plan and inform him that those areas should not be cleared," Justice Craig said.

"What caused him (Grant Turnbull) to think that it was not necessary for him to disclose that fact at the time when the matter was before the Court is not explained."

Outraged at what he regarded as officialdom's ongoing intrusion into his family's affairs, the older Turnbull shot and killed Office of Environment and Heritage officer Glen Turner on the road outside the property nearly two years ago.

Additional illegal land clearing was discovered by field officers, who used aerial photography and satellite imagery, less than a month after the killing.

"As a consequence of the clearing that occurred between January, 2013, and 31 July, 2014, significant environmental harm was occasioned. The acceptance by all four experts that remediation is required, satisfies me that an order for that work should be made," Justice Craig said.

He said the illegal clearing "involved a breach that had significant consequences", and caused the loss of local endangered ecological habitats, including feed trees known to have been used by a population of koala and likely habitat for the Grey-crowned Babbler.

Grant Turnbull purchased the property in January, 2012.

Almost immediately Ian Turnbull became involved in a long-running dispute with the Office of Environment and Heritage over illegal land clearing.

The elder Turnbull was initially charged with illegally clearing native vegetation by bulldozer on Grant Turnbull's property and an adjacent property, Strathdoon, owned by his grandson Corey Turnbull. Grant and Corey Turnbull had invested $5 million to buy the two properties.

The dispute over illegal clearing on Colorado and Strathdoon culminated on July 29, 2014, when Glen Turner and a colleague, Robert Strange, went to inspect the properties.

Turnbull spotted them and, armed with a rifle he kept in his ute for shooting wild pigs and kangaroos, raised his weapon and repeatedly shot Glen Turner without uttering a word.

Last month, Turnbull was found guilty of murder after a five-week trial. Victims statements were heard this week and he is expected to be sentenced at a later date.

In a 28-page judgment, Justice Craig said because of several circumstances identified he couldn't be satisfied that "without a restraining order in place, Mr Turnbull will adhere to the provisions of the Native Vegetation Act in conducting his farming activities on Colorado".

Justice Craig found 508 hectares had been cleared on the property, as opposed to the 29.4 hectares Turnbull had conceded had been cleared in contravention of the Act

Turnbull did not deny clearing the land but challenged the extent of the clearing of native vegetation and the terms of the remedial order, during the proceedings.

The farmer argued the economic consequences of the remedial work was estimated at $3,948,000 over the next 15 years, while fencing off the area to be rehabilitated was estimated to cost $406,560.

He said the cost "would have significant ramifications for the viability of his farming activities" and would significantly diminish the value of his property.

Justice Craig rejected Mr Turnbull's arguments that the remediation work would cause economic hardship.

"First, he advocated, supported by his experts, that rehabilitation should and would be undertaken in order to compensate for the clearing that he acknowledged to have been carried out in contravention of the NV Act," Justice Craig said.

"Secondly, ... no evidence was given by him as to the financial consequences of complying... I have no evidentiary basis upon which to determine that the cost of the remedial works in the applicant's proposal is disproportionate to the cost of implementing

Justice Malcolm Craig also imposed a restraining order on Grant Turnbull to stop further clearing.Turnbull was ordered to pay cost.