Here is a summary of the laws in my state;
When can I use a Farm plate?
You may use a farm plate if the truck is used primarily in conjunction with the operation of a farm and the farmer's private transportation. A truck may not have a farm plate if the truck us used for retail delivery, timber harvesting, or for for-hire related work. There is no limit on how far a farm truck may travel based on the registration. However, see question number 8 for limits based on inspection.
plated trucks may operate in Maine in the same manner as Maine farm-plated trucks.
What are the restrictions on a Farm plate?
A farm-plated truck is limited to use related to farming and the farmer's personal and family transportation. A farm-plated truck may obtain either a full or partial inspection. If a full inspection is obtained, then the truck is not limited as to distance for registration and inspection purposes.
If a partial inspection is obtained, the truck is limited to a 20 mile radius of the farm, and the name of the town must be painted on the sides of the truck. The partial inspection includes running gear, steering mechanism, brakes, exhaust system, and lights, safety glass and tires.