On August 11, 1997, at 1730 central daylight time, a Cessna A188B, N91919, operated by Dakota Ag Services, Inc., collided with the terrain during an aerial application maneuver during a calibration flight in Britton, South Dakota. The 14 CFR Part 91 flight was being conducted in visual meteorological conditions without a flight plan. The pilot received minor injuries. The airplane was substantially damaged. The flight originated from Britton, South Dakota. The pilot reported took off with 140 gallons of water on board so that he could calibrate the spray equipment since the airplane had not been used for liquid application for awhile. When spraying the first field he noticed that the monitor inside the airplane which is used to show how much chemical is being dispensed was giving an erroneous reading. He also realized at this time that he had forgotten to fasten his restraints. He reported that en route to the second field he managed to get three of the four restraints hooked. Upon reaching the second field, he stated, he descended over the field and turned on the spray. He reported, "I am not certain what I was looking at inside the cockpit - if it was the monitor or the one remaining shoulder strap that wasn't fastened - but I remember feeling the airplane hit the ground and start to vibrate." He continued to report that he then pulled the airplane up to an altitude of about 200 feet above the ground and made a turn toward a road in case he had to land. He reported that immediately after entering the turn the airplane began to descend until it impacted the terrain.