On August 12, 2015, about 1600 central daylight time, a Grumman G-164B agricultural airplane, N311AL, lost engine power shortly after take-off near Sac City, Iowa. The pilot was not injured and the airplane was substantially damaged during the forced landing. The airplane was registered to and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 137 as an agricultural flight. Visual meteorological conditions prevailed at the time. According to the pilot, he changed the engine oil the night before and completed a 45 minute engine run. On the accident day, he performed a normal run-up and everything appeared normal. He noted a 50 rpm drop per magneto during the engine run-up. He then departed down the runway and lifted the tail at 60 mph and accelerated to 80 mph. Shortly after getting airborne, he felt the airplane was not preforming as it should. The airplane was able to climb over a set of wires, but the engine power faded. He advanced the engine controls full forward, and then selected a cornfield to perform the forced landing in. During the landing, the airplane nosed over and came to rest inverted. Due to the un-harvested corn field, the airplane remained on site until about November 7, so an engine examination was not performed. The pilot added that he thought the engine's blower/supercharger had failed, since the engine didn't stop, but seemed to lose power. A completed NTSB 6120 form was not returned by the operator.