The pilot reported that he had completed his night rating in January and had decided to practice his night flying techniques. After completing an inspection of a mine site he returned to the circuit for landing practice. He had completed one satisfactory touch-and-go landing and was on an approach for a full-stop landing when the accident occurred. He reported he was unhappy with the approach and decided to complete a go-around from about 30 ft above ground level. Having opened the throttle, the pilot moved his right hand to the trim wheel to remove the significant amount of nose-down trim that was still applied. As he did so the throttle returned to idle and the combination of low power and nose-down trim caused the aircraft to touch down heavily. The nosewheel, firewall and propeller were damaged. The pilot then brought the aircraft to a stop on the runway. The throttle friction had been set so that it was loose. This contributed to the power reduction when the pilot removed his hand from the throttle. The pilot also reported that he had concentrated his attention on the area of the runway near the expected point of touchdown and not the far end as he had been taught. As a result, he did not recognise the last minute descent until it was too late to recover.