On September 29, 2007, at 1720 eastern daylight time, a Grumman G-164A, N8761H, registered to Salem Spray Service, Inc., operating as a 14 CFR Part 137 aerial application flight, experienced a partial loss of engine power while maneuvering in the vicinity of Pittsgrove, New Jersey. The pilot made a forced landing to a corn field, the airplane nosed over inverted, and received substantial damage to the airframe. Visual meteorological conditions prevailed and no flight plan was filed. The commercial pilot reported no injuries. The flight originated from Salem, New Jersey, on September 29, 2007, at 1655. The pilot stated he initiated a spray run from east to west at 10 feet parallel to the rows. The pilot completed a trim pass on the end of the rows, pulled up to 50-feet and heard a "pop" sound. The airplane started to descend and the pilot applied power. The rpm came up to 2300 to 2400 rpm and the airplane continued its descent. The pilot was attempting to level the airplane when it collided with the ground and nosed over inverted. The engine was removed and examined by the FAA. The fuel and oil elements, and housing were removed, and no contaminants were noted. An access plug on the engine was removed and the two cam rings were observed through several engine rotations. A compression test was conducted, and cylinders 1, 5, and 8 had low compression. The rocker covers were removed and valve action was observed through several engine rotations. The valves were "staked", and a compression check was completed resulting in low compression. A valve lash check was completed and no anomalies were noted. The cylinders were removed, inverted, and filled partially with gasoline to determine if any valve leakage was present with negative results. Visual examination of the valves revealed no burnt valves. The pistons displayed no indication of burning and no anomalies were noted with the ring gaps. The valves were removed from the cylinder head assemblies and neither the valves or the valve seats were burnt or scored. No foreign objects were noted in the cylinders, intake and exhaust ports, and exhaust manifolds. The supercharger impeller was examined for evidence of wobble or play and no anomalies were noted. The magneto covers were removed, inspected for rotation and sparking, and no anomalies were noted. The FAA concluded, "After performance of the above listed items, it was determined that three each cylinders have lost compression for undetermined reasons."