Duncan,

Once a compounds dissolve, they do dissociate, so I am uncertain of the
point of your comment about them.

In neutral pH, CaCO3 has a solubility of only about 14 mg/L in water.
Calcium bicarbonate is considerably more soluble, but it takes the presence
of a lot of free CO2 to form it in solution, and as the air only contains
about 0.03-0.04% CO2, you pretty much have to bubble CO2 through the water
to form appreciable amounts of the bicarbonate, or give it lots of time to
react and reassociate. Calcium nitrate, on the other hand, is about a
million times more soluble at about 1200 grams/liter. Given that, the ion
in solution - depending upon the pH and other dissolved species, of course -
will be the same, and is equally absorbable by plants.

Be careful how you read that water report. Instead of showing dissolved
ions individually, many municipal water systems report "alkalinity" in terms
of calcium carbonate content. In reality, it is the measure of the amount
of acid it takes to lower the pH a certain amount - a measure of the
acid-buffering capacity - and it is not a specific ion, but is made up of
carbonate and bicarbonates of a variety of cations, usually calcium,
magnesium and sodium. Based upon the solubility alone (14 ppm), it is
unlikely there is 130-250 ppm CaCO3 in your water supply, which would
provide about 50-100 ppm Ca - it's probably a lot lower than that, and if
you consider that in a 125 ppm N fertilizer solution (MSU RO formula), there
is about 75 ppm Ca, it's no wonder that in the water is insufficient.

There is some recent evidence that shows a plants' usage of Ca is determined
in part by the Mg present, as well.

--

Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies. Books, Artwork, and lots of Free Info!


"Duncan Vincent" wrote in message
...
hmmm my reply dissappeared. wasnt a very good one anyway. CaCo3 doesnt
dissolve very well were as nitrate does. I believe that the calcium in
water is actually calcium bi-carbonate and it can only exist in soloution.
My high school chem is a bit fuzzy but the ion logic sounds about right
however dissolved and disasociated arent the same thing. I grow Hydro and
i cant say absoulutly that calcium bi carbonate will not supply plants
with the amount of Ca they need. Our water here in Calgary is quite high
in Ca( 130-250 ppm CaCO3 according to the water treatment plant) but i
will get Ca deficency if I dont add nitrate. According to Wikipedia CaCO3
reacts with your stomach acid and turns into CaCl, which is soluble.

"Ray B" wrote in message
...
I agree with Steve.

Whether the source of the calcium is a carbonate or nitrate, in solution
the calcium is in the form of the ion Ca++, and that is absorbable by
all.

--

Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies. Books, Artwork, and lots of Free Info!


"Steve" wrote in message
...


Duncan Vincent wrote:
The calcium found in water is almost totally unabsorbable by plants(or
humans for that matter). Makes my blood boil every time i see a tums
commercial telling people that it "contains calcium that your body
needs".
Calcium nitrate is very readily absorbed and is very cheap.


Really?? I'm surprised that you would say that.
I can't say much about plants and what they can absorb, in the way of
calcium. On the other hand, Tums is calcium carbonate I believe. The
calcium supplement that my physician wants me to take and the same one
my wife's doctor wants her to take uses calcium carbonate as the calcium
source.
I'm aware of the vitamin D connection and humans absorbing and using
calcium and I'm aware that calcium citrate is an alternative as a
calcium supplement. As I understand it, calcium citrate can be absorbed
when taken without food but calcium carbonate should be taken with food
because stomach acid is required to make it absorbable. I suppose people
taking strong acid suppressors would need to keep this in mind.
Sorry to emphasize the off topic half of your comments but if you are
going to convince me that Tums are not useful as a calcium supplement,
I'll need more information before I believe it. (Feel free to prove me
wrong. I like to learn.)

Steve