> 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.