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Re: My current thinking on soils (subject to change)

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.