In article ,
Chris Hogg writes:
|
| I don't think the presence or absence of calcium has any direct
| influence on the accessibility of iron. It's pH that does it. As pH
| increases from a low value, say 3, iron forms insoluble hydroxides.
| Ferric iron is precipitated at a lower pH than ferrous iron, but at pH
| values above 7, both are pretty insoluble. High pH soils are most
| commonly associated with the presence of chalk or dolomite, hence the
| perception that calcium is the cause, and the inaccurate naming of
| ericaceous plants as 'lime haters'. AIUI it's no more complicated than
| that.

Oh, yes, it is! Most "lime haters" will grow quite happily in soils
which are alkaline primarily from magnesium, but not ones that are
alkaline from calcium. I did a bit of chasing up on this, and the
academic/scientific papers made it pretty clear that the calcium
caused the iron to become inaccessible to most plants in some way
that magnesium doesn't.

Yes, the inorganic chemistry is as you say, but that is only part
of the story, and the rest of it is the biochemistry of chelation,
as involved in soil ecologies. And there the state of knowledge is
that it is more complicated than it appears.


Regards,
Nick Maclaren.