During an aborted takeoff from an alfalfa field near Eltopia at approximately 1500 Pacific time, the Cessna 172 was substantially damaged; the pilot and passenger were uninjured. While on a cross-country flight, the airplane developed a rough engine and the pilot made a precautionary landing in a nearby field. After the successful landing, the pilot checked the airplanes engine and systems but concluded that …everything seemed to be working fine and elected to attempt a takeoff from the field. During the takeoff roll, the airplane rose into ground effect, but then drifted down. The pilot aborted the takeoff; however, the airplane encountered rough uneven terrain and nosed down.