> From: Scott Busby <busby at primenet_com>
> I'm curious to know exactly what laterite is.  I've seen it mentioned
> in numerous aquatic plant books.  I've also read that it is very
> beneficial to plant growth.  I would like to know its composition,
> methods for using it, and US sources where I can get some.  

It is available from Dupla (check Pet Warehouse). Theil Aquatech also 
supossedly has some.

From "Modern Aquascaping", George and Karla Booth, 1994:

       Most plant books recommend that some additives be put in the substrate
       to enhance plant growth.  Substances like peat, potting soil, sand and
       clay are often mentioned.  "The Optimum Aquarium" recommends the use
       of laterite in the lower one third of the substrate.  The book is
       lacking in specific reasons for using laterite, but leaves the
       impression that the main reason is to supply iron to the plant roots.
       One clue to the real function of laterite and substrate heating is the
       claim that they "integrate the substrate into the aquarium".  The
       following information is credited to Jeff Frank and provides more
       insight into what this may really mean.  Hopefully, we haven't
       introduced too many errors in our paraphrasing of his comments.
       Laterite is a remnant of volanic rock which has been highly weathered
       by exposure to tropical temperature, precipitation, and forest derived
       humic acids over geologic time.  Laterite, or any clay for that
       matter, has a crystalline structure which has many negatively charged
       sites which are important for plant chemistry.  Except for decomposed
       organic matter there are no negatively charged sites in the aquarium.
       Soils from temperate regions (clay fractions of which are relevant for
       comparision to the tropical laterite) not exposed to the accelerated
       wheathering of the tropics retain too much Ca++ and Mg++ which will
       adversely affect hardness and pH in a plant tank.
       Many sources agree that ammonium is the preferred form of nitrogen for
       plant utilization.  Ammonium, and many other positively charged ions
       like Fe++, K+, Ca++, Mg++, and Na++, are attracted by the negatively
       charged sites provided by the laterite.
       The negative sites attract and hold the ammonium ions like a magnet
       until a plant root hair exchanges another positvely charged ion for
       the ammonium (adsorption) and takes it in to metabolize into amino
       acids, and ultimately protein.  By providing this readily usable
       source of nitrogen, the additional benefit of removing ammonia (due to
       ammonia/ammonium equilibrium) is realized.  Instead of just the "ammonia
       to nitrite to nitrate" cycle in biologic filtration, the "nitrogen
       cycle" and its accumulating nitrate levels is avoided altogether.  The
       nitrogen ends up being removed from the tank as you cut and prune
       excess plant tissue because plant tissue is partly made of protein,
       which is 14% nitrogen.
       The substrate heating coils are an important element in the substrate
       for a number of reasons.  The primary reason is that the substrate
       immediately around and just above the cable is heated a few degrees
       higher than the ambient water and rest of the substrate.  This
       provides a gentle convection current, bringing nutrients into the
       laterite area of the substrate where they can held and made available
       to the plant roots.  Cables work well in this aspect, compared to a
       heating pad or other methods, since the spacing between the coils and
       being positioned slightly above the tank bottom provides a
       fireplace-like draft.  The slow current is important because it better
       matches the rate at which reduction reactions occur (as compared to
       the flow created by an undergravel filter).  This allows for a better
       utilization of the available nutrients.

> I have asked a local nursery and was told that the EPA banned its use in
> the US.  Comments please.

HAHAHA.  It's amazing how creative the excuses can be when a shop
keeper is asked for a product they don't carry.