Kaolin has about the lowest CEC among clays, as it is highly leached. Any clay helps hold water and some nutrients as compared to quartz sands though.

As far as clays go, kaolinite has relatively low CEC since it is a 1:1 clay. Because it is 1:1 almost no isomorphic substitution occurs. Isomorphic substitution is the replacement of Silca, with a charge of +4 with other cations with a lower charge, i.e. Al3+, Mg 2+. This results in a higher net negative charge. The negative charge is what allows cations to stick to it, hence 'cation exchange capacity'.

So do we think that on balance quartz sand with say 15-25% kaolinite will be noticeably better for crop production than the more typical pure sand?

If you can get them more or less uniformly blended, I think so. It will at least give you some improvement to cation exchange capacity while also providing more water holding capacity than sand alone.

Whereas organic matter blends itself in sand, via biological action, burying lumps of clay at my previous garden (pure sand, except for the OM I would top dress with) resulted in such lumps being still there, undivided, years later.

Vegetable roots, and water, stayed out of them, for different reasons I imagine (water drains too fast to penetrate clay, and roots go where the soil is easier to penetrate). So very fine tilling would be recommended.

According to the descriptions I read yesterday, one of the features is that the kaolinite is well blended into the sand, in proportions ranging from 5 - 40%. Sounds like it could be good as far as it goes.

The region in question is only a few miles from where we are now, so I'm going to start prowling around soon and feeling the soil on random plots of land...

Just drove through an area of it and saw some very lush growth of grass on ground that was definitely not saturated, not swampy, 3-foot high green thriving grass at a time of year when the typical such situation is dormant brown grass. Stopped on the roadside and felt the sand, and found a residue of clay on my fingers. Not a lot, guessing 5 or 10%, and yet a very notable difference in drought-sensitive grasses.

I have blended sand and local sphagnum peat moss into silty clay loam. When it is not clammy wet, it blends beautifully in my soil. Different combinations of different clays may work differently.

The addition of clay of any sort improves compost quality. The best way to incorporate clay is as a slurry. Dry clay until it can easily be broken up with a hammer or anything similar. Add that clay to a bucket and stir it with a stick or a paint mixer on a drill. Use a watering can to wet the compost pile as it's being built.

Way off-topic, bluegoat. Seems likely you posted without reading a thing.

I live near where aluminum ore and kaolin clay is mined. The kaolin is used for high heat ceramics. It's my understanding the clay has a high base of aluminum where other clays have a more diverse chemical make up.

At any rate, where a stockpile of the clay bleeds on to surrounding ground, nothing grows. I garden with a clay sand mix and love it over topsoil. But I would never use a kaolin clay for gardening.

The high aluminum mineral content of the soil (especially in central Arkansas) is more responsible for plants not growing in your area than the clay, itself. It's important to remember that all clays come from parent materials...and while the final form of kaolinite is considered a determined structure, there's still parent materials in various levels of "decay" and "freed substances" from the parent materials surrounding this clay.

The high aluminum soil parent mineral soil sources found in a lot of AR (gibbsite and boehmite, especially...which is a major mineral soil component in AR) along with the combination of low pH in the area soils makes the aluminum content highly available to plants.

Aluminum is very toxic to most plants and the low pH making it available in soils with an already higher-than-normal content from parent materials is a "perfect storm" of undesirable soil for a lot of plants. Luckily, it's relatively easy to raise pH (compared to trying to lower it) in order to greatly lessen aluminum soil availability for plants.

While kaolinite clays do have aluminum parent minerals...some parent materials, especially with pH influence, are more plant toxic than others with their availability. Gibbsite and boehmite are especially easily broken down, reactive, and made available in soils since they are bound mostly with oxygen and hydrogen rather than comprised of more complex structures.

This post was edited by nc-crn on Mon, Feb 10, 14 at 1:41

That's interesting, NC.

Florida soils have high aluminum, indeed - I know it is a major problem for veg growers. It's another reason gardens here need unusually large amounts of OM.

I'll see if I can discover what the parent materials of the kaolinite are.

Take a look at this description of highly weathered aluminum rich soils by a UF soil scientist when you guys have time. I can't pretend to really understand it, and also she is not necessarily describing the kaolinite region of central florida although I think it applies:

Here is a link that might be useful: white clay hills

Just found a reference from a book by CE Weaver stating that the parent of the central and south florida kaolinite is montmilloronite, which would quite promising if so, yes?

I'm not very good with FL soils, myself. I can get a grip on inland southern soils a whole lot easier.

The coastal-formation and near-coastal soil types trip me up a bit because they can be so much of a mix of old + young + carried sediment parents. Along with the issue of salinity influence, it can be quite a journey of soil types just over a few counties of land even if they share similar properties on how you'd manage them.

For instance...and phew...

I guess, though on the ground - so to speak - the sands appear fairly homogenous. Typical vegetative growth is likewise quite consistent seemingly determined largely if not entirely around the degree of moisture in the soil.

I've gardened with a number of clay soils (almost pure pottery grade) and found them all to be a good base for a highly fertile soil mix with the one exception of the almost pure kaolin clay found near aluminum ore deposits. What is odd is that a number of plants and trees grow on exposed areas of the aluminum ore but not on the kaolin clay. The one plant that survives in the clay is cattails.

This may be called "off topic" but I recall reading an article(sorry I can't remember the title, but it was not under gardening) it had mentioned that some people of the African continent ate kaolin clay on a regular basis for it's minerals (or vitamins?). There must be something they are craving and being rewarded by eating it, any answers?

Well, the locals in this area of florida used to be called "clay-eating" crackers, something I didn't understand because most of the soil is nothing but sand. Now that I know about regions with clay deposits it makes more sense, combined with the fact that people subsisting on local food were often hungry.

Pls, I think the aluminum connection that apparently exists with kaolinite is likely to be more of a problem for crops than the benefits of the clay.

As far as heavy metals go [and including aluminum] It matters whether they are in an organic form or in an inorganic form plus whether they are bound or unbound. The link below goes into this.

Here is a link that might be useful: heavy metals