One appliance and crew from Buckingham and one from West Ashland attended.
A barn, measuring around 10m by 30m and containing around 100 tonnes of baled straw, was well alight when they arrived.
The incident generated multiple calls to Thames Valley Fire Control Service.
The firefighters used one hose reel jet. They remained on the scene over night to ensure the fire did not spread from the barn.
Thames Valley Police was notified.