The pilot reported that he was doing a practice engine-out short approach as part of his pattern work. He went through his "GUMPS" checklist on downwind and noticed mowers near the runway. During the approach he divided his attention between the "aimpoint, airspeed, and tractors" next to the runway and "failed" to put the landing gear down. The airplane landed wheels up on the runway and was substantially damaged. The pilot reported that there were no mechanical malfunctions associated with the airplane reference the accident flight.