The pilot was undertaking an outlanding after failing to complete an attempted 150 kilometre soaring flight. The selected landing area was large and flat and was sparsely covered by grass. After a normal touchdown the aircraft rolled for about 100 metres before the landing gear collapsed. The aircraft slid for a further 50 metres before coming to rest with substantial damage to the fuselage undersurfaces. The pilot reported the landing surface was very rough, probably due to the earlier movement of cattle during wet conditions. He was not sure that the roughness of the ground could be determined from the air. This accident was not the subject of a formal on scene investigation.