On July 28, 1994, at 0700 central daylight time, an Air Tractor AT-301, N3611Z, operated by a commercial pilot engaged in aerial application, struck a roadway and nosed over during an attempted takeoff at a private airstrip near Halstad, Minnesota. The airplane sustained substantial damage, and 320 gallons of water mixed with pesticide were spilled. The commercial pilot, the sole occupant, reported no injuries. Visual meteorological conditions prevailed for the local flight, no flight plan was filed. The flight operated under 14 CFR Part 137. The pilot stated although the weather was good at the time of the event, the previous evening had produced heavy rain showers in the area. He reported the grass strip was heavily soaked and was soft and spongy in feel, and resulted in a longer than normal takeoff roll. The pilot stated the airplane barely lifted off at the end of the grass strip, and "...was in such a tail low (attitude)...that the tail wheel struck the ditch bank. This action forced the tail into the air and the aircraft hit the ground on the other side of the road causing the aircraft to roll completely onto its back." The airplane had been loaded with 320 gallons of ASANA chemical and water mix for a total load of 2,720 pounds. The basic weight of the airplane with 8 gallons of oil and 50 gallons of fuel was 4,283 pounds. Computed weight and balance showed the airplane to be 7,003 pounds at 22.62", placing the center of gravity inside the aft limit by .38" but 2,003 pounds over the recommended gross weight of 5,000 pounds. This airplane was certificated as a restricted category aircraft, with structural requirements of FAR 23, February 1, 1965, as amended. Flight criteria, propulsion, system and equipment items were certificated Appendix B, CAM 8, November 15, 1951, as amended. The Agricultural Aircraft section of CAM 8 states in part: "...it is not required that a maximum weight be established as an operating limitation for agricultural aircraft." This airplane was flight checked and displayed appropriate placards in accordance with the procedures outlined in CAM 8.