I’m unaware of any companies or organizations that are using RFID for precision farming—if by “precision farming,” you mean the ability to control tractors and other equipment precisely via technology. Advanced machinery often employs GPS and other locationing technologies that do not require radio frequency identification.
RFID sensors are being used to sense temperature, moisture and sunlight on various areas of land, in order to ensure that the proper amount of irrigation is being applied. Here are some articles that might be of interest to you:
—Mark Roberti, Founder and Editor, RFID Journal