The pilot was intending to take off from the grass Runway 02 near the Runway 02/13 intersection. After taxiing on the grass along the side of Runway 13, the pilot positioned the aircraft just before the Runway 02/13 intersection for the power checks. Once complete, the pilot taxied onto Runway 02 just forward of the numbers; however, he found it difficult to establish the precise edge of the runway on the grass and so taxied beyond the edge of the runway before turning left onto Runway 13/30. After crossing Runway 13/30, the aircraft taxied onto soft ground to the side of Runway 02 where the nosewheel dug in and the nose leg broke, allowing the propeller to contact the ground. On reflection, the pilot realised that it would have been better to have turned right onto Runway 02 following the power checks to start the takeoff from the numbers.