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Re: Laterite
Robert H wrote:
> Steve wrote:
> > The term laterite or
> > later-soil is so vague and imprecise in geophysical terms that its
> > largely a moot point.
>
> So would I infer from this then that the aquaria definition of laterite
> is then just a broad term applying to most any soil substrate?
The aquaria definition is borrowed from the scientific definition. It
does not refer to just any soil substrate, it refers to those types of
soil substrate additives which can be legitimately qualified as laterite
in the scientific sense.
The problem with the term laterite is that it does not refer to a single
homogenous material with a single chemical composition; it is a very
large class. The terms for various types of clay minerals on the other
hand, refer to specific chemical, mineral compounds. Anyone who had done
a significant amount of research on The Web about soil science will be
aware of this. Laterite refers to many vastly different mineral
compounds. It can refer to soils which merely contain a large proportion
of iron and aluminum hydroxides. It need not be a "pure" mineral to
qualify as a lateritic soil. In fact, if you were going to choose a soil
for your garden, laterite would be a poor choice because it lacks many
important minerals necessary for plant growth.
To head off a misconception, the clay textured mineral component which
is common in soils, is almost always a mixture of several of the "pure"
clay minerals and contains all sorts of "impurities". It will also be
mixed with silt, sand, gravel, rocks, leaves, insects, worms, bacteria,
humus, and other organic material which is in some stage of
decomposition.
As a medium for hydroponic growth in the aquarium, laterite has two
advantages:
i) laterite is relatively inert and non reactive. The lack of minerals
is not a problem because it is used in a hydroponic methodology where
almost all the nutrients are in solution. The property of being inert is
not intrinsically good or bad. It may be desirable to minimize other
effects such as oxygen demand or the release of humic acids or the
release of carbonate pH buffers but it depends upon the overall
strategy.
ii) laterite has available iron (I believe) which stimulates growth by
providing iron in the substrate. High levels of iron in solution, while
they might stimulate growth, would also stimulate the growth of algae.
Iron in the substrate also plays a roll in stabilizing phosphates and
may play a role in providing these to the roots of aquatic plants. Other
soils can also perform this role (I believe)
> The
> physical properties then can vary from one manufacturer to another?
No, the physical properties of any laterite based substrate additive
will probably be relatively consistent, although there is possibility
for variation. No manufacturer is going to use bauxite as laterite for
example. Suitable aquarium laterites would share the following
characteristics I think:
a) pH would be between 6 and 7 although it will probably not contain
significant buffering capacity. Almost certainly there will be no
carbonates, or sulphates and virtually no organic compounds.
b) the texture will be somewhat fine. Some particles may be sandy in
texture but there will probably be some that are clay like in texture as
this is important for the availability of iron.
c) the chemical composition will probably contain high amounts of iron
hydroxide but may also contain iron hydroxide. There could also be
"impurities" such as silicates and trace minerals. These could improve
the nutrient suitability of the additive without altering its primary
characteristic of being relatively inert and having minimal affect on
pH.
There are a broad range of other possible (non laterite) substrate
products which could be manufactured. These may or may not have pH
buffers (i.e. humic acids as from peat), might have organic material
(peat or humus for example), might have sequestered minerals of many
kinds. The texture could be primarily coarse such as sand or extremely
find like sand. The method of application and the other methods of
fertilization would be tailored according to the substrate materials.
The emphasis could be primarily hydroponic or geoponic.
> The research I have done thus far from scientific sources on the net
> have a much clearer definition.
The definition of laterite may be expressed in clear terms but is vague
in the sense that it includes a great many significantly different
materials. Geologists do not like the term laterite because it is not a
precise classification. It does not refer to a single mineral compound.
I also believe that among geologists, there is not agreement about how
the term laterite should be used: in the narrowest sense or in the
broadest sense. The term is not used consistently in the literature.
> If it is so commonplace that laterite
> exhists in North america, then it only makes sense that it would be
> documented by someone and known by someone, anyone in the scientific
> community.
I don't know what Robert's point is with this statement. He seems to be
saying A implies B; B is false therefore A is false. Both of the
assertions (A->B and not B) seem doubtful.
And I still don't know what the point of Robert's original posting was.
I think he is now saying that he is questing for information about
laterite. The North American angle seems to be a false trail. ;-)
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!!!
References: