The airplane collided with the terrain and nosed down, following a loss of engine power during an aerial application flight. The pilot reported he made two swath runs over the field he was spraying. He stated that during the turn at the end of the second pass, the engine started to lose power. The pilot reported that he made a turn to the right to avoid a farm and checked the magnetos to no avail. He stated that he made another turn to avoid another farm and trees along the flight path. The pilot reported that he decided to land in a pasture and that turbulence was encountered when the airplane descended below the tree level. He reported that the airplane impacted the ground due to the loss of the headwind. The airplane contacted the terrain on the main gear, nosed down, and spun around 180 degrees before coming to rest. The reason for the loss of engine power was undetermined.