After departing on a local flight, the pilot of the motor glider crossed a ridge line into a valley at an altitude of about 8,000 ft mean sea level, and then glided to the south in search of lift, but was unsuccessful. He decided to land on a brown, flat, field that appeared to be recently tilled. The pilot set up for a landing, and then deployed the glider's sustainer engine. The engine did not start, so he continued his approach to land. During the landing, the right wing struck the ground, the glider ground looped, and was substantially damaged. The flight manual for the sustainer engine advised that, the sustainer engine should only be extended and started when there was suitable terrain for landing within gliding distance, and furthermore, below 984 ft above ground level, starting attempts were to be avoided "so as to have a safe height left for planning the approach pattern should the engine fail to run!" The pilot stated that there was no mechanical malfunction or failure with the glider, and that he would recommend trying to start the sustainer engine at a higher altitude..