Re: soils/laterites

The following post also appeared in Aquatic Plants Digest V1 #90
Saturday, 27 May 1995 and was forwarded to me courtesy of Neil Frank.
> The following is taken from a February 1995 post with a few 
> additional comments.
> [F]{P} Soil Tests (incl. laterite)
> by Neil.Frank at launchpad_unc.edu (Neil Frank)
> Date: 13 Feb 1995
> Newsgroup: alt.aquaria,rec.aquaria,sci.aquaria
> In a recent post Shaji noted a similarity in Dupla laterite and
> composted cow manure.  I carefully re-examined the test data
> (which included replicate samples among many printouts) and
> discovered a reporting error for two materials -- ***the Dupla
> laterite was mislabled as a top soil, and visa versa.***The complete
> results (with correct labeling) are now presented.
> -----------------------------------------------------------------
> -----------------------------------------------------------------
> Code    Description                 Abbr.    Description
> ----------------------------------  ----------------------------
> APL 	Aquarium Products laterite  	 HM%  Humic Matter, % by vol.
> Lm  	back yard loamy soil           W/V  weight per vol.
> DL  	Dupla Laterite                 CEC Cation exch. capacity
> KL  	Kitty Litter                   BS%  Base saturation, %CEC
>     	(i.e. Montmirillonite clay)    Ac   Acidity
> PM  	Peat Moss                      pH   Hydorgen-ion activity
> TS1 	Top soil (Black Kow brand)     P-I  Phosphorus Index
> WD 	Soil (from Winn Dixie)         K-I  Potassium Index
> CM  	Cow manure (black Kow)         Ca%  Calcium, % of CEC
> TS2	top soil (black kow2)          Mg%  Magnesium, % of CEC
> THD	Tetra Initial D                Mn-I Manganese Index
>                                     Zn-I Zinc Index
>                                     Cu-I Copper Index
>                                     N    Nitrate nitrogen
> -----------------------------------------------------------------
> Soil HM% W/V CEC  BS%  Ac pH  P-I  K-I  Ca% Mg% Mn-I Zn-I Cu-I  N
> -----------------------------------------------------------------
> APL 0.0 0.96  3.6  89 0.4 6.4 009   12 58.7 28.5 51   041 182 004
> Lm  0.5 0.76  5.8  66 2.0 5.3 005   38 46.5 15.8 625+ 049  18  -
> DL  0.2 0.95  7.6  90 0.8 6.3 008   88 65.6 18.1 625+ 242 318 008
> PM  0.3 0.12  8.8  28 6.4 4.1 004    8 17.0 10.2 98   036  16 002
> KL  0.0 0.55  9.4  36 6.0 4.4 042   58 13.8 19.5 68   133  60 001
> TS1 0.7 0.75 10.2  61 4.0 5.0 007   6  52.8 6.8  28   011  12 044
> WD  0.2 0.56 16.5 100 0.0 7.2 166+ 502 54.4 30.4 461  369 250  -
> CM  0.2 1.01 26.6 100 0.0 7.5 166+ 502 71.7 18.9 309 999+ 256 161
> TS2 0.9 0.78 32.6 100 0.0 7.0 166+ 502 76.9 15.4 171 999+ 544 294
> THD 1.0 0.84 38.2  80 7.6 3.8 003  104 65.6 13.1 554  157 118 031
> -----------------------------------------------------------------
> The tested materials are presented in ascending order of cation
> exchange capacity.  CEC tends to be high in clay and organic
> soils.  Near the top of the list with the lowest CEC are the two laterites
> (AP and Dupla), peat moss and kitty liter (a montmirillonite clay). Laterite
> and peat moss are obviously good for growing plants, so this suggests that
> CEC may not be that important. Also included in this group is a loamy soil
> from my backyard; note the similarities to the laterites. I have used this
> in tanks with excellent results. Note that iron is not included in these
> tests. Soils are rich in iron, so the Dept. of Agriculture doesn't bother
> with these tests.
> Some observations on the low CEC materials:
>     * The CEC for the laterites are mostly Ca & Mg. The others
>       are less basic.
>     * The Dupla laterite has high Mn, Zn and Cu and moderate
>       amounts of K and a little bit of N. It has a very small
>       percentage amount of humic material
>     * The AP variety has less K and N, and much less in other
>       trace elements. It has no humus.
>     * The kitty liter has moderate amounts of P & K.
>     * Peat moss is low in Ca, Mg and other micronutrients. It is
>       also low in NPK, but in quantity in the substrate may
>       provide a long term supply of many (all?) nutrients.
> The high CEC materials are cow manure, one of the top soils, a
> cheap grocery store soil and Tetra Hilena D.  The first three are
> relatively rich in NPK, Among these, the Tetra product has very
> low pH, virtually no P, but moderate K and moderate N. The Tetra
> product is different than all other materials. It appears to be a mixture
> and may include something like peat moss.
> Also shown is another sample of Black Cow brand top soil, from a different
> 50 pound bag.  It is dramatically different.  Although
> its black color and its W/V are the same, the second sample has
> many more nutrients and may in fact have toxic amounts of
> micronutrients (e.g. Zn, Cu) if used in quantity in the substrate.  This
> highlights the potential problem in using large amounts of soils without
> testing and or experimentation.

I presume this was an analysis that Shaji had performed. Were there any
other double blind samples aside from the Black Cow? It is possible that
the contents of the bag were not completely homogeneous and one needs
to establish the repeatability of measurements to determine if a sample
is representative.

Why would the (presumed composted) manure be so low in humic matter?
I don't understand something here. [quiet peanut gallery!]

Humus is a good material to have in a substrate because it contributes
high CEC and is relatively completely decomposed. The humic acids are
very beneficial for plant root processes. Interesting that Dupla
laterite contains as much humic material as cow manure. You don't
suppose those guys are BSing us do you George? ;-) [pun intentional]

I'm not familiar with the units of measure; are these in ppm?
In particular what does a zinc index of 999+ indicate? It does not
make sense that there would be a large concentration of heavy metals
in cow manure, OR DOES IT?

Is there any measure of the relative amounts of (non-humic) organic
content? I'd have thought that the composted manure preparations
(cow, chicken, mushroom) would be nearly all organic material and
you would need to mix these with silt, sand, or clay.

In searching the gardening stores, I found almost nothing that
could be used as a sterile source of silt, sand, or clay. The potting
soils all contained large amounts of peat moss which is very desirable
for (tropical) house plants and bedding plants. I'm not sure that
this is ideal for aquariums (although Neil may argue that point :-)

It looks like earthworm castings may be a good source for humus.
I skimmed an article on composting for gardens which describes how
you can create your own earthworm castings from your composter.
As a safe source of N/P/K it would seem that solid fertilizer tablets
in the substrate. There must also be sufficient Fe in the substrate
since many fertilizers contain sulphates and sulphates are important
for plants too.

How come they didn't mention Fe in the analysis? Is it so common in 
soil that its not a factor? Maybe in large scale agricultural
operations, no one considers adding Fe; gardeners need to use it
from time to time esp. with house plants and flowers. Certainly
we need to be concerned about Fe since it is a factor in preventing
formation of excess H2S.

The Ca% & Mg% are misleading since these represent the relative
contribution to CEC from those components, not the relative
concentration. I would presume (but it's not indicated by this
analysis) that natural laterite would be relatively low in Ca and Mg.
It seems to indicate that these are important to CEC in soils
which do not contain humic matter (? with Dupla there)

Still waiting to hear from Karl Schoeler about what goes into
Substrate Gold. Almost certainly there are additives to improve the
quality of this substrate additive.

Steve in Vancouver BC

P.S. maybe laterite is not the same as Laterite! ;-)