On May 18, 1995, at 1845 central daylight time, a Schweizer G- 164B, N48532, sustained substantial damage when it nosed over after landing on a private sod airstrip in Hatton, North Dakota. The commercial certificated pilot reported no injuries. The local 14 CFR Part 137 flight operated in visual meteorological conditions without flight plan. The pilot stated he took off with a small load of chemicals to spray a field. When finished, he returned to the airport to pick up another load of chemicals. The airplane touched down and while on the initial landing roll, the pilot stated, the airplane's tail started to rise as the airplane rolled on the soft sod. In an attempt to lower the tail, the pilot applied elevator pressure. As he did this, the tail wheel locked up and the pilot lost the ability to steer around an extremely wet area on the runway. Upon reaching this wet area, the airplane nosed over. The pilot stated that due to the soft, wet condition of the sod runway, approximately 1000 feet of the runway was unusable. He also stated his "...main problem [was] my approach to landing was a little to fast."