After arriving at the steep hillside field to which he was going to apply chemicals, the pilot maneuvered at low level over the field in an attempt to determine the best pattern to fly to accomplish the job. During that process he inadvertently allowed himself to get in a position from which the airplane was not able to climb over the rising terrain. Although he dumped his chemical load and leveled the airplane's wings, the airplane impacted the terrain about 75 feet below the top of a ridge.