The Grand Forks Herald had a story this past Saturday on how farmers and ranchers are in a waiting game, waiting for FAA approval before they can use UAVs on their own land. Currently only research flights are being flown out of the test site near Carrington, North Dakota.
They have had better success with fixed wing UAVs than with quadcopters with stability and range for acreage covered per flight (around 640 acres/hour for a Trimble UX5). Current fights are using thermal and infrared imagery to look at crop health.
In the greater farm budgets, UAVs are relatively inexpensive, with models ranging from $500 to $10,000.
As of now, Trimble is one of four companies (as mentioned in past posts) that have approval from the FAA to fly UAVs, so if the UX5 was operated by a Trimble operator, it is currently legal in the United States to fly it for agriculture operations.