The commercial rated pilot was performing an aerial application run when a “puff” of smoke came from the engine. Immediately after the puff of smoke, the engine lost power, but kept running. The pilot tried to return to the airfield, but the airplane would not maintain altitude/airspeed. The pilot then elected to conduct a forced landing in the rice field. During the landing, the airplane rolled for 50-150 yards before flipping over onto its back. The pilot was not injured; however, the airplane sustained substantial damage in the forced landing. A visual inspection of the engine failed to identify the reason for the loss of engine power. At the time this report was submitted, the pilot had not returned a completed NTSB Form 6120.1, (The Pilot/Operator Aircraft Accident/Incident Report), as requested.