Re: soil works, Dupla doesn't (for me)
Paul Krombholz commented in response to Steve Benz:
> Steve Benz, Tuesday, July 23, described plant damage in a tank set up
> according to the Dupla formula. He got one sword plant to grow much better
> in a pot with some topsoil covered with gravel, while its twin continued to
> look sickly in the laterite.
> This is the first I've heard of the Dupla method having any problems. The
> brown edges that spread inwards do not sound like any kind of nutrient
> deficiency that I know of. It seems more likely to me that your plants are
> suffering from some kind of toxicity in the soil. If the plant growing in
> topsoil is doing fine, then the problem couldn't be a water-borne toxicity.
> I noticed that you felt that it was risky going with potting soil. One
> comment is that presently you are using topsoil, which is quite different
> from potting soil. Topsoil is mostly mineral, and potting soil is almost
> completely organic, being mainly composted bark and peat.
Neil Frank's analysis of Dupla laterite shows that it contains humus
at about .2% and his backyard loamy soil contains about .5%. You do not
want too much humus however it must be important since Dupla either adds
a small proportion or ensures that their laterite contains it. Loam,
laterite and the top soil samples contained similar amounts of Phosphorus
(although manure and some soils could contain a LOT more). If one were
using potter's clay instead of a commercial laterite I suspect you will
find less humus. If you were using some type of DIYS laterite, Paul's
comment about a toxic component is possible. I doubt if a commercial
laterite would have anything that toxic. I wonder if a combination
of factors including nutrient deficiency could produce this odd type
of leaf formation?
I think it's quite important to remember that the Dupla method requires
that nutrients are introduced to the tank regularly either as fish food
or as nutrient supplements. While even a relatively infertile soil
will produce strong growth for a period of time, nutrient reserves in
the soil can become depleted over time. That's why PMDD or similar
supplements used in conjunction with many substrates works very well
especially in a tank with very intense lighting such as sunlight,
MH or a bank of good fluorescents. My feeling is that there are
many, many factors to consider but that we don't know enough about
plant nutrition to exceed the possibilities of a good soil. Aqueous
fertilization seems to be important but I'm quite sure that this
alone is also not sufficient for optimal health of the plants either.
Another important point is that not all aquatic plants are suited
to the same types of substrates. Swords do like a fertile substrate.
Aponogetons may not.
Steve in SUNNY, HOT Vancouver (but still cooler than Atlanta ;-)