The pilot reported that she was attempting to take off from a cow pasture. She landed the airplane in the pasture the previous day due to a loss of engine power. She reported that the loss of power was due to debris in the right fuel tank, which was subsequently removed by a mechanic. She measured the length of the field and found it "shorter than our typical requirement," but elected to continue with the flight due to the downhill slope of the field. The owner of the pasture mowed a path for the takeoff and the pilot and her husband inspected the takeoff area for rocks and other obstructions. She also determined a "no-go" point on the ground in case the airplane did not accelerate adequately. She removed all unnecessary items from the airplane and prepared for takeoff. During the takeoff roll, the airplane did not accelerate as expected. She aborted the takeoff past the designated no-go point and was unable to stop the airplane before it collided with a fence post. The airplane caught fire as the pilot was exiting the cockpit. Structural damage to the left wing and fuselage resulted. The pilot received second-degree burns. The pilot reported that there were no mechanical malfunctions or anomalies during the takeoff roll. Although she had previously practiced soft-field takeoffs on paved runways, she had no experience with actual soft-field takeoffs.