Devin and Others,
I just looked up an internet article by Aaron Talbot from the Greater
Washington Aquatic Plants Association on the subject of "mineralized
topsoil". Let me make a few comments.
First, all topsoils are not the same. Pick up any book on soil science
and you will see that topsoils vary all over the map. So, a "cheap
topsoil" may be one thing where you live and something quite different
a few states away. Or at the next Home Depot.
Second, "mineralization" will necessarily reduce the amount of complex
organic materials in the soil. My own feeling (and apparently the
feeling of just about any horticultural expert you find) is that for
most plants a degree of complex organic material is generally
desirable. In the wild, most of the plants favoring a watery life are
growing in what are called "muck" soils, being those with more than
50% organic matter. Why should we think that plants will like it
better in mineralized soils?
Third, mineralization will not remove all organic compounds, even if
you do a hundred cycles. There is a certain amount of irreducible
carbon in all soils. Most times this is what is known as "lignin", a
stubborn, intractable filler and strengthener of plant cells. While
this does not contain any of the big three nutrients (NPK), it is
carbonaceous. Charred material, like charcoal, is another thing that
will never be mineralized by the process described. All carbon can be
removed by a process called "calcination", which means you roast the
stuff at very high temperature. But that will make your typical soil
look like crumbs of fire brick.
Fourth, the additions of clay and dolomite and such seems to have been
conjured without any science at all. While it is possible that
choosing proportions in such a haphazard manner might achieve
something of value, without a system of evaluation of some sort the
chances of success are very low.
Fifth, many people (including me) believe that the key to success with
many plants (aquatic or not) involves an assemblage of symbiotic
microorganisms interacting with the roots or other tissues in order to
assist the plant in acquiring proper nutrition. Repeated wetting and
will either kill such assemblages or distort the species mix to favor
the harsh treatment mineralization involves. Consequently, what the
plants see initially is depleted of what is probably desirable. While
the desired microbes may well be introduced as an inoculant when the
plants are put in the substrate, the population will have to grow and
displace whatever other microbes might be there after the substrate
manufacture. Or need to grow a population anew.
Sixth, I have found that algae growth is a fitful thing and trying to
make your set-up averse to algae will usually make it less friendly to
other plants. After all, green plants are green plants, most having a
set of favored conditions in common. The key thing is for the target
plants to thrive. If that means putting up with some strands of algae,
that's the price you pay. Get a couple of algae eaters.
Seventh, and finally, no matter what the current substrate fad is, it
is invariably endorsed by exquisite pictures of flourishing plants
accompanying the puffery. The Talbot article is no exception. No
question about it, those are nice pictures. The problem is that we
(and Talbot) have no way of demonstrating that the luscious growth is
due to the mumbo jumbo described. To do that he would have to show a
series of tanks, all planted the same way with plants of equal vigor,
differing only in the substrate.
One never sees such comparisons. As a scientist, I think this type of
article belongs in the same category as weight loss advertisements
showing some 19 year old babe in a bikini and implying that anyone
using the pills will look like that in just a few months.
I encourage substrate experimentation. But I sure wish I'd see some
science behind the next Great Breakthrough.
Ted Held, curmudgeon.
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