The pilot’s final approach to Runway 28 at Croft Farm was witnessed by the ground radio operator. He stated that the aircraft appeared lower than he would normally expect to see similar aircraft on finals. Subsequently, the aircraft clipped a field of crop approximately 60 ft before the runway’s threshold, impacted the ground and slid a further 50 ft before coming to a halt. Both occupants were able to vacate the aircraft without difficulty or injury. The pilot attributed the accident to his misjudgement of the aircraft’s height on finals.