Akadama users: if akadama becomes unavailable?

[Leo in N E Illinois]

I don't doubt that Turface does not work for acid loving plants for you, but do you have a source for the 20% calcium stat? Because that doesn't align with my understanding of the composition of Turface (confirmed here by the manufacturer), or PH tests that others have run (see, e.g. chart A here).

For the benefit of the group - here is via copy and paste the manufacturer's description of the components of Turface
"PRODUCT DESCRIPTION: Must be an illite clay with 60% minimum amorphous silica. Material must be processed in a rotary kiln operation at temperatures not less than 1300 degrees Fahrenheit. Product must then be screened and de-dusted. TYPICAL CHEMICAL ANALYSIS: SiO2 - 60% Fe2O3 - 5% All other chemicals at less than 5% and include but not limited to : Al2O3, CaO, MgO, K2O, Na2O and TiO2"

Reading the manufacturer's analysis, it clearly states that 35% of the components include, but not limited to "Al2O3, CaO, MgO, K2O, Na2O and TiO2". Al2O3 is Aluminum oxide, CaO, is Calcium oxide, MgO is magnesium oxide, K2O is potassium oxide, and Na2O is sodium oxide, and TiO2 is Titanium oxide.

These chemicals in the list of the 35% generally are poorly,, or partially hydrated, and exist in the voids between the amorphous silica crystals. Unlike the silica, they are available to some degree to interact with soil moisture. Hydrostatic bonding keeps the bulk bound up, but there is a slow release of the various cations.

When these dissolve in water, they become the hydroxide forms, commonly known as caustics, or lye in the case of sodium, are strongly alkaline, or very high pH. They do quickly convert from hydroxides to carbonates if atmospheric carbon dioxide is available. The carbonates tend to function as buffers, and tend to hold pH to the alkaline side of the near neutral range. Most plants want soil moisture film at the root tips to be in the mildly acidic range.

Considering the fact that Calcium is the one of the most common cations in the surface soils environment, it is reasonable to estimate that the bulk of the list of the 35% will be Calcium. I include magnesium in with the calcium as its chemical behavior is quite similar. So I support my argument, using the same reference you cite to dispute my point of view. The 20% is a number I vaguely remember from soils classes, but could be wrong, the point is, the calcium component is significant, and exposure to soil moisture over time can liberate some portion of this calcium and or magnesium. Both are a problem for azalea when the azalea are exposed beyond a certain threshold level.

Calcium and Magnesium are necessary nutrients for azalea and all ericaceous plants. BUT azaleas, and most ericaceous plants evolved to survive environments where calcium and magnesium are very limited resources. Azalea and many ericaceous plants will actively scavenge calcium and magnesium from the environment, they expend metabolic energy taking up these normally limited nutrients. They have not evolved an "off switch", to turn off uptake once nutrition needs were met. The result is, if your azalea encounters more calcium or magnesium than it needs, it will continue to take up the cations, until the azalea actually ''poisons'' itself with excess calcium or magnesium. Since I can't or chosen to not change my water (RO water is expensive) I choose to limit the calcium in my media, to avoid taking the total calcium over the azalea's metabolic needs or tolerance. Turface is fine for species that do have a way to block uptake of excess nutrients, many species that are listed as salt tolerant species do have this capacity. That is why JBP seems to do fine in Turface, as it is noted as a relatively salt tolerant pine.

 

[sparklemotion]

I'm not following the stoichiometry that you're using to get from CaO being "less than 5%" to "a bulk of the list of the 35% will be calcium."

I'm not claiming that 5% calcium is insignificant, and I grok the rest of your post (except for the magnesium part -- it was my understanding that azaleas are particularly likely to need magnesium supplements as opposed to being overdosed -- I need to look into this more). I just want to make sure that I follow how 5% jumps to, say, 17% (a "bulk" of 35%)

 

[Anthony]

What if akadama was a very hard, durable material in the early days ?

Or Mayo - dama is a high clay, with about 15 % CaO and the same in iron.
The particles at this size [ ] are very durable in use, the large particles to
the boulder size give off clay constantly.
Good Day
Anthony

 

[Leo in N E Illinois]

I'm not following the stoichiometry that you're using to get from CaO being "less than 5%" to "a bulk of the list of the 35% will be calcium."

I'm not claiming that 5% calcium is insignificant, and I grok the rest of your post (except for the magnesium part -- it was my understanding that azaleas are particularly likely to need magnesium supplements as opposed to being overdosed -- I need to look into this more). I just want to make sure that I follow how 5% jumps to, say, 17% (a "bulk" of 35%)

Your are right, the stoichiometry doesn't add up. I did ''kind of'' pull the number out of my ass. But the weasel words I'm relying were the manufacturer's claim that the list was not limited to the oxides listed. As I was composing the above I realized the issue is the total metal oxides, not the calcium alone. Key is that this list shows that 35 % of the content of Turface is one metal oxide or another. What do oxides do when dissolved into water? They become an alkali - a hydroxide. What do acid loving plants hate - alkaline conditions. When the metal alkali salts encounter carbon dioxide in water, they form carbonates. Carbonates tend to buffer solutions to an alkaline pH, and they add to the buffer capacity of the soil water film. This means that the root tips need to expend more metabolic energy to buffer the soil water film to the pH range the root tips require, a mildly acidic pH. Any addition to the buffer capacity (total alkalinity) of the soil water film will make this more expensive metabolically to the plant.

Yes, all plants have a capacity to buffer the soil water film to the ideal pH range that is required by the plant to absorb nutrients. The capacity or strength of this system varies from species to species. Plants noted for being adaptable tend to have robust systems for modifying the root environment. Delicate species tend to have less well developed systems. An instance of this in orchids was published in an article by James Asher. A prof from U of Michigan. I believe the article was 1998 maybe 1988. He took microprobe pH meter, to Sumatra and measured pH of soil water film of roots of an orchid growing on limestone rock, pH was slightly acidic at the root tip, I think around 6.2 and the water film away from the plant running over bare limestone was over pH 7 by a significant amount.

So if you overwhelm the plants ability to modify its local root tip environment, the root tip will not grow, may even die back.

About MG being a required nutrient - yes, if you are growing azalea well, which means they are not struggling to keep roots alive, the combined effect of irrigation water, & potting media has a total alkalinity effect that is less that the tolerance limit for azalea - then in this situation you might have to supplement small amounts of magnesium. Usually added as magnesium sulfate, not added as magnesium oxide. The sulfate will not kick the pH way up. You usually don't have to supplement Calcium, only because it is so ubiquitous that the azalea is getting it from the environment. But if you do have very low alkalinity water (low TDS) you might also have to supplement Calcium with the magnesium. But this is unusual, most of the lower 48 states have municipal water that is either medium or high in dissolved calcium. So it is rare that calcium must be supplemented except in situation where the grower uses rain water or RO water only.

So Turface in my conditions, with my 225 ppm TDS water with 180 ppm as calcium carbonate total alkalinity, my water combined with Turface is a bad choice for azalea and acid loving plants. IF you have low TDS / low alkalinity water, then Turface probably would not be a problem. But for me, Turface is a problem and the above is why I think it is a problem.

 

[sparklemotion]

But for me, Turface is a problem and the above is why I think it is a problem.

I just want to say that I really appreciate these thoughtful answers. I've read a lot of inorganic aggregate comparison posts/comments/guides/etc., but none have touched on these specific aspects of the soil chemistry, and I honestly hadn't been able to figure out how people who hate turface so much could be so pro-DE when they seemed to have essentially the same properties.

 

[milehigh_7]

I just want to say that I really appreciate these thoughtful answers. I've read a lot of inorganic aggregate comparison posts/comments/guides/etc., but none have touched on these specific aspects of the soil chemistry, and I honestly hadn't been able to figure out how people who hate turface so much could be so pro-DE when they seemed to have essentially the same properties.

Just a quick drive by as I have lesson plans to do. DE holds roughly 40% more water than clay-based absorbent products. Much of the way turface holds water is via surface tension and the bonding properties of water and therefore the water is outside of the particle. DE holds it inside the particle leaving the space between particles open for oxygen. I will post a quick picture of some DE that was in the bottom of a pot, having been watered in the morning on a 120F day. You can see that the particle is damp however there is no free water in the aggregate at all. This is how it is in a pot as well. The wet is obviously on the right side, on the left is how it appears when it dries.

With turface and other things that hold the water with surface tension, water fills the spaces and prevents the oxygen from being present thus drowning the plant, or at least to a degree.