The private rated pilot reported that he flew a normal traffic pattern to the grass strip airport. During the final landing approach, he was lined up with the runway but a little bit low for the approach. He stated that he knew he was low and for an unknown reason he did not advance the throttle to arrest the airplane's descent. This resulted in the airplane's landing gear contacting the bean field. When the gear contacted the beans, the airplane nosed down into the ground and was damaged. The airplane came to rest on the end of the grass runway. The airplane sustained substantial damage to the firewall and fuselage. The pilot was not injured. When asked if he experienced any mechanical difficulties with the airplane, he responded that there were none and that the airplane was operating perfectly. Based on this information the pilot failed to maintain a proper glide path during the landing approach and then failed to use available engine power to arrest the descent, resulting in an undershoot and collision with terrain.