On March 4, 1995, at 1130 Pacific standard time, a Schweizer G- 164A, N5450, nosed over during an attempted forced landing in a plowed field near Robbins, California. The forced landing was precipitated by a loss of engine power while the aircraft was en route to spray a field. The aircraft was owned and operated by Tolles Flying Service, Inc., of Yuba City, California, and was engaged in aerial application operations under the provisions of 14 CFR Part 137 of the Federal Aviation Regulations. The aircraft incurred substantial damage. The certificated commercial pilot, the sole occupant, was not injured. The flight originated from a private airstrip near Wagner, California, on the day of the accident at 1115. According to the pilot, after the engine quit he landed in the only available field, which was soft and wet. During the ground roll, the aircraft nosed over. Subsequent examination of the engine revealed a hole in the engine case near the number 5 cylinder skirt. Disassembly by the operator disclosed that the master rod had failed.