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Re: Soil/substrate

Thanks Niall for some useful input. You also managed to create quite a bit
of discussion. I am jumping in to counter some of the harsh words.

>I suggest that before polluting ones aquarium with soil of unknown
>composition you think twice.  If you believe laterite is what you want then
>commercially available sources in the aquarium industry may be the source
>since they are probably from a tropical source. 

I agree that getting laterite from a good source is important. I don't know
if getting it from a commercial source, however, is necessarily the best
approach. There are commercial sources and then there are 'commercial'
sources. Some laterites currently sold in the U.S. are said to come from the
U.S.  I do not know if anyone has seriously examined their chemical or
physical characteristics. I am not saying that they are bad, I am just
saying that they are of 'unknown' quality and until I hear more, I can't say
they are any different than the red dirt I have near my house. I don't use
commercial laterite, but if I did I would probably use the Dupla product,
because of this companies reputation, because it has desireable physical
properties (it quickly settles out when it gets into the water) and because
it has been widely tested by many people for growing plants including
several you report to this list. Maybe laterite or latersoils do exist in
the U.S. I would be interested in hearing more from Dave Gomberg about the
soil in the Sacramento area.

Nevertheless, using a soil of unknown composition will not necessarily
pollute one's aquarium. First, many aquarists including myself use different
types of soil for growing plants, including soils which are not laterite (at
least I don't think it is!). The use of soil, however, warrants a little
care and special treatment following its initial submergence. In some of my
tanks in which I use soil, I get it from the woods in my back yard where I
know it is not contaminated with pesticides or enriched with fertilizer
runoff. It is a clay-loam type soil that is low in organic matter. Although
much of the soil in my area is red clay, this soil has a grayish color; but
I think it still has lots of iron. Our local department of agriculture
doesn't even test for iron when they do soil tests. They claim all soils in
NC are high in iron. I don't like my red clay because it tends to color my
water and my "back yard loam" doesn't. For all I know my red clay is
laterite. Our local soil scientists at the University have told me that
laterite is an old term than has been replaced with Latersoil and they say
this category includes southern clay. 

 Since you probably want
>iron laterite and not aluminum laterite it is another reason to question the
>source. 


This is a good point. It helps remind us that all "laterites" are not
equivalent. Aluminum is supposed to be toxic to plants, although in small
concentration the effect may not be fatal. This also points out that some
'laterite' may not be better than other substrate material (including aged
fish poop). And don't forget, just because your plants are doing well with
the 'laterite' you are using, it doesn't mean that it could even be doing
better if you used something else.

>Just because the soil is red does not mean that it is pure iron
>laterite or even laterite.  There are many red oxidized soils containing
>iron that are not laterites.  Also, if you insist on using laterite or
>something from the ground, wash it continuously with distilled or deionized
>water for a long time to get rid of some of the available nitrates and
>phosphates. The iron mineral will sink in the water since it through an
>equilibrioum reaction with iron mineral and the aquarium water that the iron
>ions will become available to the plants.
>

This sounds interesting! Are you saying that one can leach the water soluble
nutrients out of soil that contains iron oxide and end up with a product
useful to plants? Will it be analagous to tropical laterite? What about the
Aluminum?
I once attempted to pre-wash my back yard dirt, but seemed to end up with
something that looked like sand! 

Neil

P.S. I did not hear Niall say that there are NO iron rich red soils in the
US. I think he says that red soil is not necessarily the same as laterite
and that iron laterite is not common in N. America!


Neil Frank      Aquatic Gardeners Association         Raleigh, NC
      The Aquatic Gardener - journal of the AGA -  now in its sixth year!!