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Re: vermiculite rationale?

>From: Paul Nicholson <paul at eisusa_com>

>>       My understanding of the use of soil in vermiculate is to get a
>>more optimal substrate particle size, not b/c of any nutrients that the
>>soil might have.

Actually, this is a minor point.  Vermiculite has a very high CEC (cation
exchange capacity) - 100 (quoted number) and therefore does a great job
holding onto positively charged cations.  What we do not know is whether or
not it actually releases the ions, and if so, is this a beneficial
component of vermiculite.  No one has done the "experiment" to show this so
if anyone tells you that CEC correlated to the bind and release they are
only partially right.  It does bind cations but the release is an event
that requires an energy input, thus it is easier to stay bound than to
unbind (general chemistry).

>vermiculite may very well be a source of iron

Nope, the only iron that presides in vermiculite has been added by the
plant substrate person.  Any iron present from nature is really not
testable.  I am almost certain that the major cations in vermicultite, from
nature, are magnesium and potassium.  Sure we want it to contain tons of
usable iron, but I am sure that it is not native.

>When I  uprooted plants, great clumps of
>vermiculite and soil would come up too, making a mess out of the tank.

Very true. I have been experimenting with this substrate and really like
what it does for holding nutrients.  I also have two other tanks with kitty
litter with a sand cap.  I like the plant growth in the vermicultite tank
better but the kitty litter tank does well too.  Uprooting plants, adding
water, siphoning the bottom of the tank can bring vermicultite into the
water column and is a MESS!!!!  Getting the stuff out is a pain.  I
recommend that if you follow this route that you use a deeper sand cap to
cover the vermiculite.

Matthew T. Mason                            "The young do not know
Doctoral Student                                  enough to be prudent,
Department of Molecular Genetics      and therefore they attempt
The Ohio State University                   the impossible -- and
mason.163 at osu_edu                          achieve it, generation
                                                            after generation."
                                                            -- Pearl S. Buck