Police are treating fires at two farms 20 miles apart as linked arson attacks.
The first blaze took place at about 03:40 BST on Sunday at a barn in Little Oxenden, Northamptonshire.
The second incident involved a "large quantity of hay bales deliberately set on fire" at a farm in Orlingbury Road, Hannington, at about 17:30, Northamptonshire Fire Service said.
A Northamptonshire Police rural crime officer said the fire was "heartbreaking" for one farm owner.
"Anyone with information regarding these incidents, please make contact," PC Hutch Hutchings said in a tweet.
"The long term destruction and loss for the farmer following this is heartbreaking for them."