[pfdietz]

There's a gardening channel on youtube I watch (RED Gardens) where the guy does all sorts of small scale experiments with organic gardening. He was a bit surprised to discover his soils have excess potassium, from the various organic materials he had been using (like wood chips for mulch; pot ash, right?) The soils were also sodium deficient, so he was thinking of spreading measured amounts of salt!

He also discovered commercial compost can be crap, since it hasn't broken down enough and soaks up nitrogen as it finishes its decomposition in the ground. So if your potatoes are struggling in something like that, slather on some urea and they'll perk (and green) right up.