The pilot of the aerial application airplane reported that the airplane was near its maximum gross weight with chemicals and fuel onboard. He attempted to take off from a turf and asphalt runway that was 2,650 ft long, beginning with asphalt and then becoming turf about one-third down the runway. The pilot further stated that all engine parameters looked normal during the takeoff roll, but when he attempted to rotate, the airplane did not leave the ground. As the airplane neared the end of the runway, he “pulled” the airplane into the air to clear an 8-ft dike at the end of the runway. The airplane cleared the dike but then settled into a marshy area beyond it, contacting trees and coming to rest upright. The airplane’s fuselage and empennage were substantially damaged during the accident sequence. The pilot stated that there were no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation and that in the future, when winds are variable, it would be wise to re-assess airplane loading.