THE PILOT LOADED THE AIRPLANE WITH 900 POUNDS OF WHEAT SEED. HE SAID THE TAKEOFF REQUIRED THE ENTIRE LENGTH OF THE PASTURE RUNWAY TO GET AIRBORNE. THE AIRPLANE WOULD NOT CLIMB AFTER GETTING AIRBORNE AND THE PILOT SAID THE LOAD WAS NOT JETTISONED FAST ENOUGH TO PREVENT THE AIRPLANE FROM COLLIDING WITH AN IRRIGATION SPRINKLER AND THE GROUND.