The airplane received substantial damage during a forced landing to a rough field following a loss of engine power during cruise flight. During the landing, the airplane's nose landing gear separated, and the airplane nosed over. The pilot reported that two hours into the cross country flight the engine stumbled and lost power. He stated that he performed emergency procedures which included cycling the carburetor heat control, selecting full rich on the mixture control, checking the fuel selector valve, and cycling the magneto ignition. He stated that the only response to these inputs was erratic firing on one magneto and no response when the other magneto was selected. He stated that he selected a fallow farm field and executed a forced landing. The reported temperature and dew point at the destination airport, about 20 miles north of the accident site, were 21 and 16 degrees Celsius, respectively. According to a carburetor icing probability chart, this temperature and dew point were within the range of susceptibility for moderate icing during cruise power.