Around 10 tonnes of waste straw went up in flames after arsonists lit a stack at Crowle.
The fire, at 10.57am on Saturday on land off Godnow Road, was put out quickly by a Crowle fire crew, who were on the scene within minutes.
A fire service spokeswoman said: “It is believed the fire was started deliberately. The crew separated the straw to deal with the blaze effectively and had it under control within a short time.”
The fire at an isolated waste straw stack was on land adjacent to a farm, but posed no danger to buildings, added the spokeswoman.
A farmer used his digger to help the fire crew deal with the incident.