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Re: Laterite
Warning: long posting.
James Purchase wrote:
> >Laterite can also create red, cloudy water if improperly used. I presume
> >this is what you mean by _colloidal_ solution. Some but not all
> >lateritic soils are claylike in texture. The term laterite refers to
> >composition, the term clay refers to texture. So your statement is like
> >saying not all round things are red!! so?
> I've never experienced any problem with red, cloudy water using Dupla
> Duplarit G. It is a granular product not a powdered one. It is much too
> early in the morning to play semantic word games - what is your point? I
> stand by my statment that an aquarist is much less likely to run into
> colloidial fouling of the water column using Duplarit G than kitty litter.
Apparently not all laterite are created equal. I have read emails from
folks who had red water following the use of Dupla laterite. Go figure.
I presume that it had something to do with the fine powders that somehow
got into the laterite. Maybe it wasn't a pure batch. Whatever.
> In my original post, I gave a URL to a reference. Did you follow it? In case
> that you missed it, here it is again - http://www.dupla.com/e037.htm. From
> an agricultural perspective, laterite is certainly considered an infertile
> medium. But we are not growing rice or corn. We are growing aquarium plants,
> in small, enclosed boxes, where we (usually) don't have the luxury of
> thousands of gallons of fresh water flowing past every minute, carrying away
> anything leaching from the substrate.
Why would we presume that there is anything leaching from the substrate?
I should hope that we would choose something suitably low in nutrient
content that would not create a problem with excessive nutrient leaching
from the substrate! We need not order special dirt from SE Asia to get a
soil which does not leach excessive N or P into the aquarium water! In
fact, top soil and subsoil if taken from a suitable place has just these
qualities. It also contains stable non reactive clay intermixed with
silt, sand and humus. Topsoil and subsoil taken from a soil horizon a
few feet below the surface is very different in chemical composition
from clay which is mined and selected for its properties in making
pottery!
> The most important nutrient supplied by laterite apparently is iron, which
> is released from it under reduction conditions in the substrate. I would
> venture to guess that what is leached out of the laterite over the
> "geological" timeframe referenced by Horst could be aluminium and other
> potentially toxic metals. Whatever is missing, we are concerned with what is
> left - and it seems to work well enough for growing aquatic plants.
I don't believe that aluminum toxicity is a concern with topsoil or
subsoil which has been subjected to normal leaching under ordinary non
tropical conditions for several thousand years (such as surface soils of
glacial origin). There are alumino silicate minerals in almost all soils
and those of us using a great variety of soils (mainly collected from
the garden), have not experienced symptoms that would indicate a problem
with aluminum toxicity. Indeed, for the most part, the general result is
very fast growth rates which decline as the nutrient value of the soil
is reduced by consumption. Add a clay ball with fertilizer or a Job's
stick and growth rates dramatically increase again.
> I would venture to guess that Horst and Kipper (Dupla) recommend laterite
> based upon their measurements and observations in both the field and in the
> lab. They noticed a particular physical phenomenon in multiple tropical
> streams and disovered it's source - laterite. Their testing in the lab
> confirmed that it works in an aquarium.
TOA only compared the growth of plants in laterite against those grown
in sand. They also did a comparison with CO2 fertilization. No mention
is made of comparisons with other more fertile mediums. I don't have any
problem with the Dupla system. I'm sure it works extremely well as an
hydroponic system.
> Steve, your wife has family in the Philippines and I believe that you have
> said that you visit there every couple of years. I, and I'm sure a lot of
> others, would love to hear what you have seen in the the brooks and streams
> there - what is the substrate material found in places where lots of aquatic
> plants grow?
The soil of the Philippines is all of volcanic origin at some point in
time. I don't know how long ago those volcanoes started making soil or
if there are lateritic soils there. The colour of the soils which I saw
in exposed cuts were always red which indicates a high iron content.
Volcanic soils tend to be rather rich in several kinds of trace
minerals. I don't know if some of the soils qualify as laterite. The
rocks which I saw in the areas around Iligan look to me to be of
volcanic origin from their porous, pitted black appearance. I could
obtain rock and soil samples if anyone wants me to mail them. Probably
won't tell us much though. I never got to the region of Mindanao famous
for the Philippine Crypts. That's near Zamboanga and I don't travel
there yet.
I have not been able to travel widely in quest of aquatic plants in the
Philippines because it is not easy to travel in the back country; very
rough territory. As well, where my family lives is quite close to the
Muslim city of Marawi and it would not be wise for me to go to far
afield! Still we travel and I will report more on my next trip if I have
a chance. You might be able to find the report I made following my last
trip. Search for the phrase Tinago, Iligan or Ditucalan; that should be
unique. I don't know how far back the archives go.
I did find aquatic plants growing in spots. Interestingly, they grew
either in thick black mud bordering the edges (emerse plants) or in the
reddish sand of a submerged spring. Presumably, those plants were
getting nutrients from the underground stream source. It is a clean
source, not high in bacteria or nutrients conducive to bacteria. It is
the main potable water source for the city of Iligan. I would bet there
were high levels of reduced Fe dissolved in that spring water just as
Horst and Kipper discovered in certain regions. There were no Crypts
there, only a single species of Limnophila.
The rivers of the Philippines can be either raging torrents of dirty
brown water coming from the mountains, or bordering the ocean, slower
but with heavy deposits of silt and heavy growth of emersed aquatics.
Where the plants grow the thickest, is in heavy, thick, black, stinking
mud. I'm not suggesting that this is suitable for an aquarium; its
simply that growth occurs most where nutrients are plentiful.
> As I type this, I'm looking at a tank setup using your HTBASS method.
> Several days ago, I finally worked up the energy to trim some of the massive
> over growth of the stem plants in this tank. I uprooted a lot of plants in
> the process and they all had extensive root systems. I didn't encounter any
> major problem with clay particles clouding the water column. But I did
> notice a very stong "tint" to the water - tannins are still leaching out of
> the soil layer. The topsoil used was a very dark, sandy topsoil over a layer
> of clay subsoil. I perform 20% water changes per week on this tank and it
> has been running for four months. The tannins don't bother me visually, nor
> do they seem to bother the plants or the fish (Cardinal Tetras, Dwarf Neon
> Gouramis and Dwarf Rams). From my experience with this setup so far, this
> substrate is only now beginning to come into it's own - initially some
> plants (Hygro) just wouldn't grow well, but now this problem seems to have
> been overcome.
I don't recall if you added peat. I would expect tannins with peat but
not so much with a topsoil. Interesting observations nonetheless. At
first I thought that you had collected crushed bricks from the brick
works but it sounds as if you selected a topsoil from an area where you
knew there was a natural outcropping of iron rich clay. The comment
about Hygro is interesting. read on.
> I've never used kitty litter as an aquarium substrate. I have put a cup of
> it in a beaker of water and I did observe a major "problem" with collodial
> clay particles becomeing forever suspended in the water column.
I've never used KL in a substrate either. I did try vermiculite and
earthworm castings in one of my first experiments. I would not repeat
that although I did get very impressive growth. As you observed with KL,
I didn't like the fine bits of vermiculite that floated around and
settled on plant leaves following uprooting.
Dan Q did do a number of experiments with KL. Some types worked well,
others did not work well at all. I guess if you follow his instructions,
you can have good success. Whenever there is a problem or concern about
getting soil, clay or KL into the aquarium water; I think we should all
take a leaf from the books of Karen Randall and Paul Krombholz. Both of
these folks use soils in pots or trays which can be removed entirely
from the aquarium to perform any required maintenance. I have set up my
75 gallon tank recently using ONLY terracotta clay pots, garden soil and
a layer of gravel. So far so good.
> It's not a
> substance I'd care to have in the bottom of _my_ tanks. I was able to "wash
> out" the suspended particulate, and I was left with a fine grained, dense
> (it sinks and stays "sunk") material which could be of great use (I suppose)
> in an aquarium. but when I suggested it on the list, several people
> commented that I had gotten rid of the "good bits". The CEC had gone down
> the drain so to speak. But then again, I'm still not convinced that CEC is
> anywhere near as important as some people seem to think.
Yes, I agree that CEC is not very important. I think iron availability
is a very good thing. I think mild reducing conditions are a good thing.
I think low levels of humins are a good thing. I think low but
perceptible levels of P and N fertility are a good thing. I think that
non toxic levels of trace nutrients is a good thing. I think avoiding
the kinds of soils that might contain toxic levels of certain metals is
a good thing (leached top soils, or subsoils within a few meters of the
surface or laterite)
> I've said it before, and I'll say it again.... many roads lead to Rome.
> Which one you choose depends on how good a driver you are.
I think we agree on this.
Roger S. Miller wrote:
> Welcome back, Steve. Hopefully, since you're using the list for the
> tweaking forum it's OK if someone else jumps in :).
Well, it was a good natured tweak and I hope there's some useful
discussion that follows from it.
Jump right in! (but don't get your feet stuck in the mud!)
> > Surely this will cause the LOSS of almost all the
> > nutrient value of the soil!
>
> Yep. Laterites are infertile subsoils. Strip off the top soil, and not
> much grows on the laterite underneath. In fact, it's often so rock-like
> that it can't be cultivated.
>
> > Perhaps the only important thing about the
> > laterite leaching is thus, the LOW concentration of phosphates and
> > nitrates???
>
> And most everything else but iron, aluminum, oxygen and hydrogen. Even
> silicon (a major part of most rocks and soils) is largely removed. The
> remainder is (nearly) inert.
So in addition to not having macro nutrients, laterite also is a very
poor source of micro nutrients except possibly for iron. Since, in the
Dupla regime, iron is added hydroponically, we have to assume that the
laterite is also not providing sufficient iron to satisfy all the iron
requirements of the plants. I was curious on this point; if anyone could
determine if laterite alone in the substrate, without additions of
chelated Fe, could satisfy the iron requirements of plants.
> > Why even pottery clay and kitty litter have this quality.
>
> Pottery clay and kitty litter (and most other clay products) also contain
> significant quantities of sodium, potassium, calcium, magnesium and
> silicon and proportionately lower quantities of iron and aluminum; normal
> clays shrink and swell depending on water content and composition; their
> particles are charged and they may disperse in water or remain strongly
> cohesive; they adsorb organic molecules and exchange a variety of ions.
> Normal clay minerals can also be quite unstable when they're removed from
> the environment they formed in. Some of the additional elements present
> in clays are present in exchangable sites and are available to plants;
> others (notable magnesium and some of the iron) may be part of the
> structure of the clay minerals and won't be available to plants unless the
> clay breaks down.
Sodium, potassium, calcium and magnesium are not usually a problem in
top soils especially those where the annual rainfall is quite high
unless the original rock material which the soil is derived from is
limestone.
Several of us here in Vancouver have tried a particular type of pottery
clay called Terrastone which has the following Chemical Analysis:
BaO 0.4%
CaO 0.5
K2O 3.2
MgO 2.5
Na2O 0.7
TiO2 0.7
Al2O3 16.1
P2O5 0.3
SiO2 71.5
Fe2O3 4.0
LOI 6.5
There is enough potassium and magnesium that we might be concerned if it
were in a soluble form. I don't know if this analysis indicates that all
of the minerals exist only as oxides. I notice that the total is more
than 100% so perhaps a geologist or hydrologist or potter can give us a
little more insight into what the analysis means. I don't believe it
tells us weather these elements are in reactive or non reactive forms.
I have observed that this stuff, when I used it in relatively large
quantities together with earthworm castings and gravel, did not
initially seem favourable to certain kinds of fast growing plants such
as Hygrophila polysperma. Other plants, with thick roots and slower
growing, thrived in this stuff right from the start. After about a
month, the Hygrophila species started to grow well. It could very well
be that there was enough K or Mg in the interstitial substrate water to
create some type of problem. I think this is a very important
observation about pottery clay and we should make a distinction about
the clay which is a component of surface soils.
If someone is using a pottery clay, I do encourage them to mix it with
other stuff and use it in the lowest layer of the substrate, similar to
the precautions for using laterite. Or to use it to prepare clay
fertilizer balls. It's been my experience, that the stuff I used seemed
to work quite well overall.
I would not expect topsoil nor subsoil collected from within a few
meters of the surface to have high levels of K or Mg in soluble forms
where the soil had good leaching such as on a hill or in a region of
high annual rainfall such as the west coast of the Rockies. A pH test of
the soil is a good precaution to test for calcareous soil. Limestone
derived soils are often light coloured, chalky looking soils.
> You can use the word "clay" to refer to most any very fine grained
> material and you'd be correct by one definition of the term, but I think
> that usage is deceptive. Laterite is often very hard, massive and
> rock-like and is only fine-grained if it's ground finely. Clay soils are
> almost always very fine grained, plastic when wet and easily disaggregated
> under water. Laterite is made up of iron and aluminum hydroxides while
> clay soils are mostly made up of aluminosilicate minerals, which are
> completely different beasts.
I think this is a very important distinction that most people miss when
they look for a "substitute" for laterite. Clays may contain available
iron; they are certainly not unreactive. On the other hand, pure
aluminosilicate minerals are not very reactive either. Clay is not
necessarily homogeneous. It can and does contain other metal salts and
mineral crystals depending upon where its dug up.
I think we should be looking for soil candidates that are leached of:
a) soluble salts such as Na, K, Mg and Ca (not difficult to find topsoil
like this except in arid regions)
b) excess N and P (avoid compost, avoid earthworm castings except in
small amounts)
c) high levels of insoluble trace metal salts (Cu, Pb, Zn, Mn, Mo, tin,
continue with periodic table)
I think you can find soils which are leached of c) without going to
tropical weathering. The tropical weather over hundreds of thousands of
years removes the silicates. Low levels of silicates are NOT critical to
growing aquatic plants at all.
Without checking the analysis of pottery clay or field testing the KL,
you can't be sure that there aren't high levels of trace metal salts.
While they are not highly soluble, they can be somewhat toxic to the
plants. Interestingly, if such a material is mixed with sand and humus
(or peat), the organic material detoxifies the heavy metals, if they are
present. The dissolved metals such as Cu or Zn are absorbed by the
organic complexes.
I'll snip the rest of the comments. I agree heartily with them and Chris
Coleman's.
I do hope that the "tropical leaching" qualities of laterite are a
little more in context now!
Steve Pushak Vancouver, BC, CANADA
Visit "Steve's Aquatic Page" http://home.infinet.net/teban/
for LOTS of pics, tips and links for aquatic gardening!!!