The private certificated helicopter pilot reported to the NTSB investigator-in-charge (IIC) that he had practiced two or three autorotations at a grass/turf covered runway that terminated with a power recovery to a hover during a CFR Part 91 personal flight. He decided to perform a touch-down autorotation, and said that he pulled excessive collective pitch during the termination of the maneuver, and accelerated too much while leveling the helicopter at the conclusion of the deceleration flare. The helicopter touched down hard and tilted forward onto its nose, the forward portion of the right skid tube fractured, and the main rotor blades struck the ground and the tailboom.