At the conclusion of spraying operations the pilot initiated a climb enroute to his destination. Almost immediately, the engine failed completely and the pilot was committed to a landing in a barley crop. During the landing roll the nosewheel was broken off and the aircraft overturned. The aircraft was at about 100 feet agl when the engine failed and the most suitable area available required that the landing be made downhill on a soft surface. A skid to the right after touchdown caused the nosegear to fail. The cause of the engine power loss could not be established.