Aug. 13/13-The BP Airspray Air Tractor AT401, C-FEKO was departing Quill Lake SK, on an application flight. Durng the takeoff run, the engine (Pratt & Whitney R-1340) sputtered and lost power. The pilot rejected the takeoff, but could not stop the aircraft on the runway. The aircraft continued 200 feet past the end of the runway into a canola field, and overturned. The pilot suffered minor injuries and the aircraft sustained substantial damage. Some of the chemical (Silencer) and some avgas was released from the overturned aircraft. The aircraft operator is recovering it for repair.