The pilot was attempting the first takeoff from a grass paddock on an agricultural operation. Take-off direction was towards the west with 700 m of ground roll available. The wind was variable, but mainly a gusting crosswind from the right at around 10 kt. The aircraft was below maximum weight with a full hopper load and about half fuel. When it became evident that the aircraft would not lift off by the end of the available take-off area, the pilot rejected the takeoff and attempted to stop in the paddock remaining. The aircraft veered to the left, collided with a fence and ground-looped before coming to a stop. The pilot reported that engine operation was normal and he was unable to explain why the aircraft did not fift off in the distance available; which should have been adequate. He believed the changing wind strength and direction may have been a factor.