Originally Posted by RigglePLC
Fertilizer and fertilizer dust strongly attracts moisture. Try to find a way to protect it from the dust. Or somehow keep it clean. And dry. New plugs will fire better. Perhaps an automotive wire-drying spray will keep you going if the problem crops up in the field.
The ignition coils are under the fan shroud next to the flywheel and you can't get to them without taking the shroud off at least.