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Re: Hybrid substrates

James Purchase wrote (over a month ago):
> "I thought
> about adding a "pinch" of peat, and/or a few Osmocote pellets on the very
> bottom, but I figure those would just be more variables that might go
> wrong..."
> True...... very true..... I would be afraid of both. A Profile/Flourite
> substrate bed is going to be pretty porus and I don't think that there will
> be any problem for water borne nutrients to diffuse into the entire bed of
> the substrate. Similarly, if you place Osmocote down there, the nutrients in
> it (and I assume that your Osmocote has the same 18-6-12 ratio as the bottle
> I have) are going to be able to diffuse out of the substrate and enter the
> water column (of course, on the other hand, the high CEC of the Profile just
> _might_ be able to hold those leaking nutrient ions down in the substrate).
> If you decide to use Osmocote, use _very_ little.

I'm pretty sure that even the most tenacious of cation exchange sites
are not going to bind up a large percentage of the NPK nutrients
especially since nitrate and phosphate are anions. Those ions have a
much much lower affinity than calcium and magnesium and the total ionic
binding capacity of even a high CEC material is not that large anyhow.

Seriously, if you want to prevent nutrients from diffusing out of the
substrate, the way to do it is to encase them inside a medium that does
not readily transmit water, such as a fine clay like pottery clay. i.e.
clay balls.

> I don't think peat would be a good idea, although it might offer a limited
> buffer against the Ca and Mg in the Profile, preventing too high an increase
> in GH and Alkalinity. My fear is that the acidic peat might cause too rapid
> a release of the Iron contained in the Profile. I don't know the ionic state
> of the iron, nor how tightly it is bound to the structure, but there is
> certainly more than you would want released suddenly. I may be wrong on
> this - Steve Pushak knows more about peat's actions than I do. But I'd say
> just go with your initial recipe without any other ammendments and then use
> water borne fertilizer.

I rather expect that the micro nutrients in all of these commercial
preparations are not actually very chemically available. If they were
chemically available, you would in fact find that they were extremely
toxic to fish, invertebrates, bacteria and to a lesser degree, to
plants. Peat has the advantage of being a form of organic material which
is most stable to decomposition, low in nutrients and thus has a minimum
of other undesirable properties. I expect that peat will prevent more
toxicity problems than it causes since the humic compounds tend to bind
tightly to large metal ions such as copper, zinc and iron. Diana
Walstad's book is an excellent read on this subject. I've finished
reading it and found it to be an excellent technical resouce; a word of
caution: this is not a picture book, its very technical but probably the
most easily comprehensible technical reference that a hobbyist might

Diana also points out in her book, that a major benefit of organic soil
or peat is that is an important supply of CO2 for the first year or so!!
CO2 is actually one of the most critical growth limiting nutrients in

I expect that these soil or clay and peat mixtures are quite good for
growing established plants with healthy root systems. They may not be a
good medium for starting stem cuttings; loose gravel is probably better
for that or perhaps a good balanced mixture of sand, silt, clay and
humus but heavy on the sand and light on the clay and humus. Plants
without a healthy root system and a vigorous transpiration system may
not root as quickly in very low redox conditions. On the other hand, I
suspect a lack of oxygen may play a role in stimulating root formation.
It's also a good bed that different plant species have adapted
differently and have differing tolerances.

On the subject of analyses of substrate materials: these long lists of
elements does little to tell you about chemical availability, toxicity
or texture. These properties are probably more important than the
elemental composition of a good amendment.

Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!