Convicted murderer Ian Turnbull, who shot dead an environmental officer investigating him for illegal land clearing, is locked in a court battle with one of his sons over the ownership of his farms.

Turnbull's second oldest son, Roger Turnbull, has taken his parents to the NSW Supreme Court, claiming they reneged on a long-standing promise to hand over farm land to him.

Ian Turnbull, left, is escorted out of court during the trial. Credit:Daniel Munoz

In a statement of claim filed in the court, Roger alleges that there was a dramatic breakdown in the wheat farming dynasty, with his father often calling him "stupid" and saying "you've made a bad choice in wife, you're getting what you deserve".

According to Roger, Turnbull consistently blamed him for everything that went wrong on the farm, including droughts, and called him away from his family for work that was not urgent.