The pilot reported that he intended to remain in the traffic pattern and practice take off and landings. Before he departed, he checked the grass/turf runway 36R to determine if it was hard enough to land on, since Runway 36L, a paved runway, was covered by ice. He decided to take off from runway 36L and land on runway 36R. He departed and flew a left hand traffic pattern. He reported that the landing and rollout were normal until the airplane hit a soft spot in the turf, which resulted in the airplane nosing over. The airplane sustained substantial damage to the wings and tail. The pilot reported that there was no malfunction or system failure of the airplane before the accident.