On October 29, 2004, about 1915 Pacific daylight time, a Piper PA-22-160, N8158D, veered off the runway during landing rollout and nosed over at the Nut Tree Airport, Vacaville, California. The pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, was not injured; the airplane sustained substantial damage. The personal local flight originated from Vacaville about 1645. Visual meteorological conditions prevailed, and a flight plan had not been filed. In a written statement, the pilot reported that the purpose of the flight was to practice landings while remaining in the traffic pattern for runway 02. After completing six touch-and-go practice takeoffs and landings without mishap, he planned to make a full stop landing, which would be his last of the day. The pilot said that during the landing roll he lost control and the airplane began to veer to the right. The airplane continued to the right, and departed off the runway surface, encountering soft, muddy terrain. As the main landing gear impacted the soft terrain, the airplane nosed over, coming to rest inverted. The airplane incurred damage to both wing struts and the upper section of the rudder. The pilot reported no preimpact mechanical malfunctions or failures with the airplane.