The agricultural airplane was loaded about 300 pounds over its maximum gross weight for a commercial aerial application flight. The pilot stated that the airplane had not become airborne after traveling 3/4 down runway 36 (2,800 feet by 80 feet, turf). At that point in the takeoff, the pilot attempted to lift off, but the airplane settled back onto the runway. The airplane then overran the runway and hit a hill after which the airplane became airborne and then impacted the ground with its right wing tip and left wing resulting in substantial damage. The pilot sustained minor injuries.