The pilot reported that he completed two successful aerial application flights from the same 2,000-foot turf runway before the accident flight. The pilot reported that the airplane was not on level terrain when the chemical was added to the load prior to the accident flight, which might have affected the accuracy of the sight gauge. The pilot was distracted during the loading of the chemical and refueling, and he did not recheck the level of the chemical in the hopper. He stated that the airplane's maximum gross weight was overloaded by about 500 pounds. The temperature was about 95 degrees Fahrenheit and the wind was from 270 degrees at 5 knots. He departed from runway 18 with 10 degrees of flaps. The airplane became airborne, but it did not get out of ground effect. He stated that a dust devil might have affected the airplane. According to the pilot, the airplane “sagged” (lost lift) and the left main landing gear hit an embankment. The airplane landed in the adjacent cornfield, and sustained substantial damage to the wings and fuselage. The pilot reported that there was no mechanical malfunction or failure of the airplane prior to the impact with the terrain.