The commercial pilot was flying an aerial application flight when the pilot observed a puff of smoke come from the radial engine. The airplane experienced a partial loss of engine power, so the pilot attempted to land at a nearby airstrip. While maneuvering to land, the airplane's descent rate did not allow for a landing of the airstrip and the airplane landed in a rice field. During the landing roll out, the airplane nosed over and came to rest in the inverted position. Substantial damage was sustained to the airplane's vertical fin. The reason for the loss of engine power could not be determined.