The pilot was departing to the north, from a private concrete airstrip, for the purpose of conducting an agricultural application flight. The airplane was loaded with 400 gallons of fungicide, and contained 110 gallons of fuel on board. Shortly after becoming airborne, the airplane began to settle back toward the runway. The pilot attempted to dump the fungicide; however, the airplane settled into a soybean field and nosed over. The airplane sustained substantial damage to the empennage, fuselage, wings, and engine firewall. The pilot stated that he did not experience any mechanical malfunctions and examination of the wreckage by a Federal Aviation Administration inspector did not reveal any anomalies. The nearest weather reporting station, located approximately 12 miles north of the accident site, reported winds from 170 degrees at 6 knots, and a temperature of 27 degrees Celsius, about the time of the accident.