Rick / Leftwood,
Thanks for the link, but it's a video so I can't watch it while at work.
http://permaculturenews.org/20...
>> "Mineral nutrients" has thrown me for a loop. Never heard the term applied to N, P and K.
I forget where I first heard it - just any plant nutrient that's absorbed as soluble ions. Probably it should technically mean something that was once a mineral and then became soluble, but then it would not apply to most (or any?) source of N. Unless you consider guano a mineral!
I think it is used widely for Fe, Ca, Mg, S, and the micro-nutrients. It makes sense to me that it should be used for K, since potassium originally came from minerals even if we "recycle it" in compost.
Similarly, phosphate comes from minerals ("rock phosphate") although compost does also contain some P from biological sources.
Maybe N should not be called a "mineral nutrient", since it originally came from air! If the term is never or seldom used that way, then "my bad". If it is sometimes used that way, you make a good point that it seems a loopy thing to call something that was fixed from atmospheric N2.
In my own mind, I thought of them as "those inorganic, soluble ions that plants take up through root hairs". So maybe I added "N" in my own twisted mind to a more common usage meaning micro-nutrients + Fe, Ca, Mg, S + K + P.
Wiki not only agrees with you that N should not be called a mineral nutrient, Wiki thinks the term applies to all living things, not just plants. And they call it "archaic".
Wiki:
"the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen present in common organic molecules. The term is archaic, as it describes chemical elements rather than actual minerals."
http://en.wikipedia.org/wiki/M...
So I probably have been using it wrong for most of my life! Thanks for pointing that out. I should substitute "nutrients taken up as soluble ions".
