The airplane had landed following a sport parachute flight. During the landing roll the nose wheel separated from the strut. The nose strut dug into the sod runway & the airplane nosed over inverted. An faa inspector examined the airplane & noted that the nut & bolt which secured the nose wheel was absent. It was not located. He stated that there was no evidence that the bolt had broken. No maintenance to the nose wheel had been recorded recently, & the last annual inspection was logged 8 months & 72 flight hours before the accident.