The private pilot was performing turns around a point, his grandmother's house, when his passenger became ill. The pilot landed the airplane in a rough pasture area near the home. The ill passenger deplaned and a relative of the pilot enplaned. During the takeoff roll the pilot stated the airplane encountered clumps of tall grass and ruts. According to the pilot, "I thought we were just about to become airborne when we hit a big rutt, this slowed us down significantly to not enable us to become airborne, but not slow enough to stop." The pilot attempted to make the airplane fly over a fence at the end of the 1/4 mile field. The airplane became airborne and its main landing gear tires struck the fence. The airplane collided with the ground shortly thereafter. The post accident investigation revealed the pilot's operating handbook did not provide information which would factor sod field operations into the takeoff distance calculations.