The 30-year-old striker joined the Magpies from League One rivals Carlisle 12 months ago and played 45 games for the Meadow Lane club last season.
County boss Chris Kiwomya told BBC Radio Nottingham that finances played a big part in the decision.
He said: "He's one of the highest earners. I've got restraints on me and I'm trying to keep the age of the team down.
"Also, he's not been playing lots of football so it made sense.
"Both parties are happy. I'd like to thank him for his contribution to the club."