Straw bales were set on fire in a field at Great Gonerby last Wednesday evening.
A fire crew from Grantham was called to the blaze in Belton Lane at around 7.15pm. They found around 150 bales alight – believed to be a deliberate act of arson.
Firefighters decided to leave the bales to burn out and they left the scene at around 10.30pm, returning the following day to carry out an inspection.
As a fire inspection found the cause of the fire is likely to be deliberate, police are investigating.
Anyone with information is asked to call the non-emergency 101 number, quoting incident number 464 of August 16.