The airplane experienced a loss of engine power while performing an aerial application turn and nosed over during the subsequent forced landing. The pilot reported that after maneuvering for approximately 1.5 hours he switched from the left fuel tank to the right fuel tank. The pilot stated that he flew another 15 minutes before the engine lost power during a left-handed teardrop turn. The pilot reported that the loss of engine power "sounded as if the fuel was starved away from the engine, such as the way it would on shut-down." The pilot stated that the engine "made about three or four burping revolutions, then quit altogether." The pilot reported that the airplane was at 200 feet above ground level when the engine lost power. The pilot stated that he advanced the mixture control to full rich, set the propeller to low pitch, and turned on the fuel pump. The engine did not restart and the pilot performed a forced landing to a soybean field. The pilot reported that the airplane nosed over during the landing rollout. Inspection of the wreckage showed that the fuel selector was positioned on the right tank. No fuel was found in the right tank, gascolator, or carburetor bowl. The interconnected left and center fuel tanks contained a significant quantity of fuel. The fuel samples collected were blue in color and free of any particulate or water contamination.