The pilot of the Cessna A188B, departed from a private grass field with approximately 100 gallons of agricultural chemicals on board for an aerial application flight. He stated that on departure he "did not pull up fast enough" and felt a "jolt" when the right main landing gear impacted a 4-foot-high gate post, later discovering that the landing gear had been sheared. He then pressed on the brake pedals to see if his brakes were operational; however, there was no pressure and "the pedal went to the floor." He applied his chemical load to the field in order to decrease his landing weight and then flew to an airport with a longer runway, assuming he had no brakes. Immediately after the airplane touched down it "broke to the right," and impacted a fence damaging the wing spar. The pilot did not report experiencing any mechanical malfunctions with the airplane.