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Re: Aquatic Plants Digest V1 #357

> From: Stephen.Pushak at saudan_HAC.COM
> Date: Fri, 22 Mar 96 18:18:08 PST
> Subject: Re: is anaerobic good?
> 
> Hmmm... nobody else is going to talk about this, so I might as well
> talk to myself. ;-) Warning: long technical article. Skip to the
> end for the summary if you're easily bored. ;-)

Hmmm...I wonder if replying to your own mail constitutes a dialogue 
or is it still a monologue :-)

I found your article/questionare very interesting, and since I am 
settting up another tank, I am pretty sure I want to use some kind of 
soil substrate this time. Biggest question, where to get the right one?
Perhaps not too many people feel comfortable with such a complex 
subject :-)  I'll be the first to admit that.
 
> What I'm trying to get at here is an optimal soil substrate for
> promoting plant growth especially by providing soluble iron and
> manganese.
> 
> Here is an extract from some material by Paul Krombholz which was
> published in TAG, Vol. 7 No. 4: "Mineral nutrition of Aquatic Plants,
> Part 2 Underwater Soils and Nutrient Availability"

Diana Walstad also published the article in TAG, Vol. 7 No. 4 titled 
"Soil substrate experiment" where she talks about different types of 
soils and their evaluation over a three month period. She is on the
technical advisory commitee of TAG and one of the most vocal 
proponents of using soils for substrate. I don't think she is on this list. 

snip.....

> > I wonder if iron oxide or steel wool could be used as an alternative
> > or supplemental Fe source for laterite?
> 
> I think it could.

So do I. However much experimenting should be  done about it first.

> In an aerobic environment unoxidized Fe will not
> be rapidly oxidized, however it will be relatively available chemically.
> Ferrous oxide is relatively soluble (the reduced state). Ferric oxide
> can be reduced by bacteria in an oxygen deficient environment to
> the Ferrous state. Steel wool or other iron compounds should be in
> the very bottom layer of the substrate where circulation is minimized
> to prevent a situation where excessive amounts of iron could be in
> solution.
> 
> > What conditions favour the production of hydrogen sulfide?
> 
> The same anaerobic conditions favourable to reducing iron, the
> bacteria and the presence of sulfates. To avoid toxic H2S formation,
> we need to minimize rich sulfer compounds in the anaerobic zones.
> This would include manure, manure compost and especially, any
> solid fertilizers containing sulfer compounds.
> 
> > Is it better to have a dense clay zone at the bottom or should there be
> > some soil to support bacterial activity in the anaerobic zone if the
> > goal is to reduce Fe to the usable state?
> 
> There should be some organics in the anaerobic zone to support
> bacterial activity. Without bacteria, Fe is not reduced.
> 
> > Is it realistic to expect that a specially designed substrate could
> > support an optimal level of Fe? How deep would it need to be?
> 
> In nature the soil depth is virtually unlimited. In an aquarium,
> eventually the substrate becomes densely filled with roots which
> provide an abundance of oxygen. At this point, Fe can no longer be
> effectively solubilized. Obviously the deeper the substrate, the
> longer before this occurs. A dense lower layer of clay will resist
> root penetration. A 6" substrate or deeper would not be too much.
> 
> > Is it still wise to add an appropriate micro-nutrient supplement
> > for other minerals and how often should that occur? Do we still
> > need to add chellated Fe, perhaps at a reduced level?
> 
> Yes. The soil may not be able to supply all Fe requirements but it
> can greatly improve the availability of Fe between dosing. Plants
> grown in my soil aquarium show less variation in red coloring when
> the Fe supplementation is temporarily discontinued than in the gravel
> only substrate.
> 

snip.....

> > Nutrients in soil can be used up. How long does this take?

I think I read this in TAG (it might have been Diana's article) saying
that it should take many years to deplete the soil.
 
> It would depend upon the amount of plants grown and the overall
> growing conditions. One can remove a large amounts of bio-mass
> from a good aquarium almost weekly. Some plants like Crypts and
> Echinodorus grow much slower. A soil substrate might become
> deficient in 6 months to a few years. I have little empirical data
> to substantiate this guess.
> 
> > Is it a good idea to add solid fertilizer (of the kind containing
> > nitrates and phosphates) tablets or sticks in a substrate? Where
> > would be the ideal level for these? bottom, middle layer?
> 
> I'm experimenting with this and other people use fertilizer or pond
> tablets with good success (notably Jim Kelly). I expect the
> best place is in the middle layer, not in an anaerobic zone.
> 
> > Is there
> > a danger of those macro-nutrients getting into the water level or
> > will the plants consume all the nutrients if the only substrate
> > circulation system is the roots of the plants?
> 
> I would presume that all these macro-nutrients get used up by
> the plants as they are drawn through the plants circulation
> system. It should be safe to use macro-fertilizers if they are
> confined to the substrate.
> 
> Here is my proposed "ideal" substrate:
> 
> Bottom: 2" fine clay or clay-like dirt. Powdered laterite
> would be a good choice here. Optionally a very small amount
> of super-fine steel wool (<5 gms) Pure clay should be mixed
> 2:1 with ordinary dirt to provide minimal organics.
> 
> Lower middle: 1.5" soil with composted manure. 20% organics.
> 
> A few low sulfur fertilizer sticks broken into small pieces.
> 
> Upper middle: 1.5" soil/manure/vermiculite.
> 
> Top: 1" to .5" layer of dark silica or quartz coarse sand.
> 
> Vancouver Steve
> 
> ------------------------------
Interesting ! I hope somebody tries it. The thin layer of sand on top 
might be too thin to prevent spreading of soil/manure/vermiculite 
into the water coulumn.
On the related subject, Dr. dave posted an article on soils not to 
long ago. In it he/she? talks about loam as the ideal substrate.Anybody
cares to elaborate on that? Where to get it, thickness of  substrate....

Franc Gorenc                        franc at golden_net
Kitchener, Ontario               http://www.golden.net/~franc
Canada