On July 3, 1998, at 0900 central daylight time, an Air Tractor AT301, N7301Y, impacted the terrain near Langdon Airport, Langdon, North Dakota. The commercial pilot was not injured and the airplane sustained substantial damage. The pilot stated that the engine lost power one mile out while on approach to the crop field to be sprayed. He said that the forced landing was made in a rough field where the airplane nosed over. The airplane was being operated as an aerial applications flight under 14 CFR Part 137 when the accident occurred. The flight originated in Langdon , North Dakota, at 0850. Visual meteorological conditions prevailed at the time and no flight plan was on file. Subsequent to the accident an examination was conducted on the engine. No mechanical anomalies were found. There was compression on all cylinders, the spark plugs had combustion deposits, the magneto sparked, and there was continuity throughout the engine. There was fuel still in the fuel tanks and no contamination was found in the fuel.