The pilot stated that he had completed three or four passes of the aerial application flight before the accident. He said, he was coming into the field, was heavily loaded, and he felt the plane mush a little bit. He got his wheels and spray rig into the wheat and it kind of pulled him down. During the accident sequence, the engine separated from the airplane and the wings and fuselage were substantially damaged. According to the pilot, the performance and handling of the airplane were great and there were no mechanical deficiencies with the airplane.