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Soil Soup


  1. Steve's nutrient method (derived from Krombholz)
    by Stephen Pushak <teban/> (Mon, 15 Dec 1997)
  2. My current thinking on soils (subject to change)
    by krombhol/ (Paul Krombholz) (Thu, 1 Jan 1998)

Steve's nutrient method (derived from Krombholz)

by Stephen Pushak <teban/>
Date: Mon, 15 Dec 1997

Kevin M. Hanson wrote:
> >Date: Sat, 13 Dec 1997 04:54:18 -0800
> >From: Stephen Pushak <>
> >Subject: Steve's nutrient method (derived from Krombholz)
> >
> >Step 6) prepare a mixture of Krombholz soil soup (mix with water to form
> soupy mud)
> Can you help me find more info on what "Krombholz soil soup" is?  I am very
> interested in your nutrient method, but I am not familiar with this
> reference.

Here is some information from a discussion in June of 96 between several
folks on the subject of soils and substrates. This comment is from Paul
Krombholz and describes the "soil-soup" method along with some other
comments. I looked for an entry in the index of TAG back issues but
didn't find it. Paul may be referring to his article in TAG 9:3, "Part 4
Homemade Nutrient Solutions" where he describes extracting powerful
nutrient solutions from soil and compost. Maybe he can give us another
reference on soil-soup.

"Steve, June 13, expressed concern about high concentrations of
nutrients released by composting. I am concerned about that. too,  I
don't think it is good to have high concentrations of soluble nutrients
in the soil of aquatic plants.  In theory they can cause osmotic damage
to the roots of aquatic plants, and nitrates in the soil can prevent, at
least until they are used up, the desirable reducing conditions that
make iron soluble.  Besides,  the nitrates are wasted if they get
converted to atmospheric nitrogen.   If I have soil that I think has a
lot of nutrients released by composting, I extract the nutrients before
using the soil for growing aquatic plants. The latest TAG describes two
methods I use to extract nutrients from soil. Just ordinary soil from
the woods shouldn't need to be extracted.  it is already thoroughly
extracted by the rains and the plant roots.  I shouldn't think that
there would be any need to extract composted soil-peat mixes because
there are such small amounts of mineral nutrients in peat.  It might be
advisable to extract soil-manure mixes before use.  I think that, for
beginners, soil-peat mixtures would be 'safer'.

"The "soil-soup" method where soil is collected and water is slowly
added with much mixing until you have something like thick soup, which
is then run through window screening or a rice strainer, produces a safe
product. The screening filters out all the roots, worms and other
critters, and other "raw" pieces of organic matter that might cause a
large oxygen demand.  About a quarter inch to a half inch of the soup is
placed in the bottom of the tank or planting tray and covered with about
a half to one inch of gravel.  Water can be added with precautions to
prevent stirring up the gravel, and almost no cloudiness will develop. 
The gravel can be put on top of the soup, and then everything can be
allowed to dry out.  The soup turns quite hard, but when water is added,
it gets soft again, and the plants seem to grow just as well.  If the
soup has been allowed to dry out, the chances of any cloudiness
developing when water is added are much less. The soup is relatively low
in organic matter, and I have found that, when a tray becomes packed
with roots, low-level iron deficiency develops, and additions of soluble
iron stimulate growth.  Soil-peat mixtures or soil-manure mixtures
beneath gravel seem to be able to supply iron for a longer time.  I have
not seen any tannins come from soil-soup, but I have seen tannins get
into the water from soil-manure and soil-peat mixtures.  A water change
gets rid of them, and they don't seem to come back."

Note: I'm not advocating beginners to try things like manure or compost!
Caution!!! :-D


My current thinking on soils (subject to change)

by krombhol/ (Paul Krombholz)
Date: Thu, 1 Jan 1998

The current thread (or is it a fuse?) on aquatic soils prompted me to
summarize my current thinking, which is subject to change if I find out
anything different in the future.

I make "soil soup"  from ordinary topsoil, gathered from a nearby woods,
which I mix with water until it is like thick soup and then filter through
a rice strainer.  I pour about 1/4 to 1/2 inch of this in the bottom of a
tank or a container, such as a baking dish, and cover with gravel.  I
consider this "soup" relatively low in organic matter that has a high
oxygen demand.  It should be fine for most species of aquatic plants except
perhaps the lace plant, which requires, in addition, companion plants
growing within one or two inches of the lace plant.

Crypts and swords will become iron deficient growing in this type of soil
setup under conditions where large plants are growing in relatively small
containers and their roots fill the soil.  The deficiency symptoms show up
in 6 months to a year, and additions of chelated iron will correct them.
My hypothesis is that the roots aerate the soil so completely that soluble,
reduced, ferrous iron compounds are all oxidized into insoluble oxidized
ferric compounds.  I do not see iron deficiency symptoms develop in an
aquarium where the entire aquarium is filled with gravel over soil soup.  I
only see iron deficiency show up when the plants are in containers, such as
pyrex baking dishes or microwave food dishes.

A soil peat mix (50:50 by volume) works better in containers for crypts,
swords and other aquatic plants that have thick, white roots (This
appearance indicates large air channels in the roots.) These are the plants
that become iron deficient when they fill the soil with their roots.   My
hypothesis is that the peat, although it is not a rapidly decomposing
product, serves as an oxygen "sink" that to some extent counteracts the
oxygen source from the roots, and this sink serves to keep reduced, soluble
iron compounds available for the roots for a much longer time.

Plants that do not benefit especially from being in a soil-peat mix, and
may be harmed by it, are the Aponogetons, Anubias, aquatic ferns, such as
Ceratopteris and  Microsorium, and others with roots that do not have large
air channels.

Happy New Year, everyone!

Paul Krombholz, trying to figure out how to keep my large collection of
aquatic plants alive following the partial distruction by gas explosion of
the science building where I have been keeping them. 

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