# What role does clay play in soil if any?



## mistergreen (Mar 3, 2007)

Here in cincinnati, if you dig down a foot, you'll hit granite and yellow clay. This whole area was covered by ocean millions of years ago and you'll find fossilized sea shells everywhere.

And of course, we have the Ohio river.

Anyways, I guess clay has micronutrients in it? And people would kiln it so it wouldn't get cloudy and go into the water in the tank in products like Flourite or Laterite?

Any other functions?


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## sandeepraghuvanshi (Feb 22, 2007)

Laterite has a very high cation exchange capacity(CEC), which basically means that it has capacity to draw nutrients like ( Fe, K, Mg, Mn, Zn, Cu, etc.,) and remove them from the water column into the substrate from where the roots can easily assimilate them as opposed to assimilation from the water column by the leaves.
All clay are not laterite.


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## TeutonJon78 (Nov 10, 2004)

Clay still works mostly the same way I believe. The difference is that clay in ground isn't a stabilized product like laterite (or Flourite, or EcoComplete, etc). Those are kiln fired (I believe) to lock them into form. I think Diana said (correct me if I'm wrong) that normal clay can pollute/cloud the water since it's more unstable.


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## onemyndseye (May 12, 2006)

".....normal clay can pollute/cloud the water since it's more unstable....."

While this is somewhat true... its not 100%  Clays mixed in the soil also can act as a natural Cleating agent (or binding agent) to keep soil particles and nutrients "bound" to the subtrata 

Bascially... A little clay in your subtrate can be a good thing... a lot can be a mess 

it also bepends greatly on the makeup of the clay in question.. I recently setup a 5Gal bowfront highlight tank with probably 50/50 Clay and soil.. Getting excellent plant growth in this tank and water that is almost un-natually clear  

One day comming home from work I passed a construction site that had dug out a huge embankment (probably 15ft tall) to put in a retaining wall... I noticed that about the first 6ft of this bank was nothing but solid clay. So I stopped and asked nicely and was able to dig out a 5 Gallon bucket full  Still have whats left of the stuff in the bucket in my store room... I just go get a handfull or two when I need it 

Take Care,
-Justin
One Mynds Eye


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## AaronT (Apr 26, 2004)

onemyndseye said:


> Bascially... A little clay in your subtrate can be a good thing... a lot can be a mess


I couldn't agree more with that statement. If your soil has that much clay I don't recemmond trying it. Rather, I would mix 1 part of that soil with 15 parts of regular dark topsoil. The soil here is full of clay too. It's dark red when you dig it up. I tried using this in a tank and it was way too much clay.

Using a soil with only about 5-10% clay helps to bind nutrients in the soild, provides iron and also acts as a flocculating agent for soil particles that get in the water column during replanting or other disturbances.


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## Robert Hudson (Feb 5, 2004)

There are all different kinds of clay, and laterite is not quit the same thing as clay. True laterite is lateric soil. It is found in the tropics where extreme heat and tropical rains over centuries strip the soil of everything except aluminum oxide and iron...very high concentrations of iron. It contains no other minerals, silica, or organic material. Dupla's Duplarit laterite, and Aquarium Pharms First Layer Pure Laterite is mined from Sri Lanka. Chances are any aquarium product "laterite" is from Sri Lanka.

Clay is a different story. Its iron content can vary greatly, it can be high in silicate and other things. Flourite is a mined, fired clay. Schultz Clay conditioner/Aquatic Plant soil/Turface is fired "Fullers earth" which is a type of clay. Soilmaster is a competitive product to Turface and is made from clay.
Eco complete and other commercial substrates are all made from clay as far as I know.

The main reason for using clay in any form is for the iron content, which was always thought to be important for plants. Clay may contain some other minerals, but its mostly iron. It is oxidized iron though, which plants can not use. Only when Fe+3 (oxidized iron) is converted to Fe+2 (water soluble iron) can plants use this. This process is done over time by organic acids, and bacteria in the substrate.

Fired clay, and I guess raw clay have good Cation exchange capacity. In simple terms it can hold nutrients from the water for future plant uptake, like a nutrient reserve.

Here is the official definition http://www.aquabotanic.com/glossary.htm#C

_Cation Exchange Capacity (CEC) 
Quantifies the ability of media to provide a nutrient reserve for plant uptake. It is the sum of exchangeable cations, or positively charged ions, media can adsorb per unit weight or volume. It is usually measured in milligram equivalents per 100 g or 100 cm3 (meq/100 g or meq/100 cm3, respectively). A high CEC value characterizes media with a high nutrient-holding capacity that can retain nutrients for plant uptake between applications of fertilizer. Media characterized by a high CEC retains nutrients from leaching. In addition, a high CEC provides a buffer from abrupt fluctuations in media salinity and pH. Important cations in the cation exchange complex in order of adsorption strength include calcium (Ca2+) > magnesium (Mg2+) > potassium (K+) > ammonium (NH4+), and sodium (Na+). Micronutrients which also are adsorbed to media particles include iron (Fe2+ and Fe3+), manganese (Mn2+), zinc (Zn2+), and copper (Cu2+). The cations bind loosely to negatively charged sites on media particles until they are released into the liquid phase of the media. Once they are released into the media solution, cations are absorbed by plant roots or exchanged for other cations held on the media particles. Anion exchange capacity Some media retains small quantities of anions, negatively charged ions, in addition to cations. However, anion exchange capacities are usually negligible, allowing anions such as nitrate (NO3-), chloride (Cl-), sulphate (SO4-), and phosphate (H2PO4-) to leach from the media. 
_

The Walstad approach is centered around organic soil, not clay. Clay is inert. Soil is rich in organic material which does break down over time. It provides macro and minor nutrients. Think about it. Plants normally do not grow in clay because clay is too void of nutrients and nitrogn. Crops will not grow in clay. Flower gardens will not grow in clay. The reason it became popular in the aquarium was to provide iron and CEC while the macro and trace elemants were provided by other sources, mostly in the water column. The Walstad approach takes it back to providing everything the plants need in the substrate via soil, including iron.

I am not saying which approach is better, or if you should mix the two together or not, but I am simply clarifying the difference between the two approaches.

I hope this information is helpful to the conversation and your inquirey

Best regards


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## mistergreen (Mar 3, 2007)

onemyndseye said:


> I noticed that about the first 6ft of this bank was nothing but solid clay. So I stopped and asked nicely and was able to dig out a 5 Gallon bucket full  Still have whats left of the stuff in the bucket in my store room


I'm lucky, I just need to dig a foot down and hit clay... If I was a potter, I'm set..



> Plants normally do not grow in clay because clay is too void of nutrients and nitrogn. Crops will not grow in clay. Flower gardens will not grow in clay. The reason it became popular in the aquarium was to provide iron and CEC while the macro and trace elemants were provided by other sources, mostly in the water column.


So is flourite, soilmaster etc... useless without adding fertilizers? 
I go on another planted tank forum and they (most of them) swear adding soil in a tank is a foolish idea.


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## Robert Hudson (Feb 5, 2004)

> So is flourite, soilmaster etc... useless without adding fertilizers?
> I go on another planted tank forum and they (most of them) swear adding soil in a tank is a foolish idea.


I wouldn't say useless exactly, but certainly not complete. Flourite really only provides iron, maybe , possibly some other minerals, but the only thing for sure is iron. Plants also need whats called macro nutrients: nitrogen, phosphate, Potassium, Magnesium, Calcium... Flourite will not provide any of those things, so you have to add them to the water or to the Flourite.

The Walstad method is more than just adding soil to the tank. It is a whole methodology, and to understand it, you really need to read her book, Ecology of the Planted Aquarium. Using this method, you have soil, supplimented with nutrients from fish food, no added C02, no added fertilizer and very few water changes. The idea is to provide a very natural enviornment that supports itself. That is what is meant by the "El Natural" type of tank by those who follow her book. Ask some of the devote followers of the El Natural method here. They have tanks which were set up following the Walstad book that have never done a water change in years and have beautiful healthy plants.


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## Robert Hudson (Feb 5, 2004)

> So is flourite, soilmaster etc... useless without adding fertilizers?
> I go on another planted tank forum and they (most of them) swear adding soil in a tank is a foolish idea.


I wouldn't say useless exactly, but certainly not complete. Flourite really only provides iron, maybe , possibly some other minerals, but the only thing for sure is iron. Plants also need whats called macro nutrients: nitrogen, phosphate, Potassium, Magnesium, Calcium... Flourite will not provide any of those things, so you have to add them to the water or to the Flourite.

The Walstad method is more than just adding soil to the tank. It is a whole methodology, and to understand it, you really need to read her book, Ecology of the Planted Aquarium. Using this method, you have soil, supplimented with nutrients from fish food, no added C02, no added fertilizer and very few water changes. The idea is to provide a very natural enviornment that supports itself. That is what is meant by the "El Natural" type of tank by those who follow her book. Ask some of the devote followers of the El Natural method here. They have tanks which were set up following the Walstad book that have never done a water change in years and have beautiful healthy plants.


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## mistergreen (Mar 3, 2007)

I understand how plants work..

but what's the idea before not changing the water for a long period of time?... In a regular tank, depending on your tap water quality, you're replenishing certain trace elements like calcium & magnesium and also take out imbalances in fertilizers/nutrients. But I guess the soil sustain a balance?


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## Robert Hudson (Feb 5, 2004)

This might answer more of your questions

http://thegab.org/Articles/WalstadTank.html


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## xavierj123 (Aug 24, 2008)

Correct me if I'm wrong but Cincinnati has limestone laid down in the Ordovician period 70 million years ago. Limestone is sedimentary rock and granite is igneous rock, not to be found in Cincinnati. Limestone is not recommended for aquariums.


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## mistergreen (Mar 3, 2007)

xavierj123 said:


> Correct me if I'm wrong but Cincinnati has limestone laid down in the Ordovician period 70 million years ago. Limestone is sedimentary rock and granite is igneous rock, not to be found in Cincinnati. Limestone is not recommended for aquariums.


true but rocks were never mentioned in this thread


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