The pilot stated that he was preparing to land at the airport and made radio calls on the common traffic advisory frequency (CTAF) to announce the airplane's position on the downwind, base, and final legs of the traffic pattern. While on the landing roll, as the airplane traveled over a crest in the runway, the pilot observed a tractor crossing the runway from left to right. The pilot steered the airplane to the right to avoid a collision, and the airplane's left wing contacted the tractor, resulting in substantial damage. The operator of the tractor stated that he heard the airplane's CTAF transmissions, but proceeded to cross because he assumed that the airplane was clear of the runway. The pilot reported there were no mechanical malfunctions or anomalies with the airplane.