The pilot was practicing solo 180-degree autorotations in preparation for a private pilot helicopter add-on rating. During the accident autorotation, the helicopter was in a left turn at an altitude of 500 feet above ground level(agl). The helicopter exited the turn "a little low and lost some rotor speed." While attempting to recover the low rotor speed, the pilot had to extend his glide path more than he anticipated due to approaching terrain and obstacles, which in turn slowed the forward airspeed. The pilot reported, "Of course I wish I had abandoned the auto at this point. I flared [the helicopter] but with high density altitude and the out of ground effect of the soybeans, I still entered the thick-drilled soybeans, which piled up on my right skid." The helicopter then rolled over and came to rest on its right side. Examination of the helicopter revealed the main rotor blades were destroyed and the fuselage was buckled. No mechanical anomalies were noted with the helicopter.