The pilot stated that the agricultural airplane was fueled with 110 gallons of fuel and loaded with 450 gallons of water and chemical mix for a local aerial application flight. The pilot then taxied the airplane to and attempted a takeoff from runway 27 (3,500 feet by 75). The pilot stated that the engine seemed normal during the takeoff roll. About halfway down the runway, the airplane did not "respond" so he began dumping the load but stopped because there was a car traveling along Illinois Route 47, which is west of the runway departure end. The airplane became airborne and impacted a tree and a power line and came to rest in a corn field about 150 yards west of Route 47. The wing spar was damaged. The pilot stated that he should have used a lesser load for takeoff.