On August 24, 2014, about 1730 central daylight time, an Air Tractor AT-401, N91968, was destroyed by a post-impact ground fire after a forced landing due to a loss of engine power near Natchez, Louisiana. The pilot was not injured. The airplane was registered to and operated by Red River Dusting Inc. under the provisions of the 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed at the time of the accident. No flight plan was filed. The airplane was departing from a private grass airstrip near Natchez, Louisiana, at 1730 on a local flight. The pilot reported that during climbout about 75 above the runway, he heard a loud "pop" and the engine started to lose power. He dumped the 250 gallons of chemical that weighed about 2,000 pounds. The airplane continued to lose altitude. He executed a forced landing to a cotton field, and during the landing roll, the airplane hit a ditch which spun the airplane around. A post impact engine fire ensued and the airplane was consumed by fire. The pilot reported that the No. 2 cylinder "swallowed the exhaust valve" and broke the top of the jug. An examination of the engine revealed that the No. 2 cylinder exhaust rocker boss was cracked. The 600-horsepower radial engine had a total of 11,534 hours of operation. The time since the last inspection was 229 hours, and the time since the last overhaul was 1,314 hours.