The airplane settled onto the runway after becoming airborne during takeoff. The airplane became airborne a second time and this time it settled into a bean field off the end of the runway. The airplane then contacted a ditch and crossed a road prior to coming to rest in another bean field. The pilot stated that the airplane was at or near gross weight, but he did not calculate the weight and balance. He stated that the engine was running normal and he was confident the airplane was going to stay airborne which is why he did not dump the chemical load.