Originally Posted by Desert Pupfish
Thanks for sharing this post. I have some questions:
Wouldn't a 3' soil level with an additional 1" cap be a recipe for anoxia, as well as a crazy amounts of nutrient leaching at first? Most of what I've read recommends half that depth for soil, so I'm wondering what you're basing your recommendation on, and how you avoid anoxia & hydrogen sulfide production?
What kind of soil do you recommend using here? There are many so-called "organic soils" all with different ingredients--even within one brand.
What amounts or proportions of greensand, azomite, & clay are you recommending, and what kinds of each? Being natural products, all can be highly variable.
I've seen Azomite recommended as kind of a "magic sauce" for many horticultural applications, but even on the company website I'm unable to to find out what minerals it contains, and in what proportion. Supposedly it's a mineral rich montmorillonite clay--just like SafeTsorb, or kitty litter for that matter. So it's not clear what advantage of this would have over SafeTsorb--which makes a fine substrate (and cheap!) in it's own right. I've got it in my tank over a thin (≈1/2") layer of organic potting soil, and most plants seem to love it. The tank has only been up 7 months, so I can't attest as to the durability of the substrate and nutrient availability. I do supplement it with low-dose Thrive for the stem & floating plants.
What kind of clay do you use, and how much? In other threads people talk about using iron-rich pottery clay. Do we know what kind of iron is in pottery clay, if it's bioavailable to plants, and does that vary with the pH or other water parameters?
If you have a link to your resource/s for this, that would be most helpful.
It would be a recipe for anoxic conditions if the lower levels of soil were restricting O2 from moving through soil aggregates. Exactly what I want. Denitrification only occurs where there is little to no O2. While the soil depth and structure are ideal for plants to root well. Hydrogen Sulfide is not as big a threat as people make it out to be. H2S will be neutralized by O2 into harmless SO4. Basically as soon as H2S moves up through the low O2 soil it reacts with O2 in the upper levels of the soil and becomes SO4. Remember H2S forms in the absence of O2 and is neutralized with the presence of O2. If your soil structure is ideal you will have aggregates of silt, clay, sand, organic matter, and oxygen at all any depth in your soil substrate.
I recommend decomposed peat humus for several reasons. It is really important in my recipe to have acidic organic matter with high CEC and no mystery nitrogen compounds causing problems cycling. Because ammonium levels become very inconsistent which is a result of the cations NH4 being exchanged with other cations in the soil and being released from dissolving sediments. So that means one day I could have a ammonium spike and the next day ammonium is no longer available in the water column because it was exchanged for calcium or any one of many cations. The positive charges associated with different cations is what causes these mineral cations to exchange charged spots on the negatively charged organic matter and clay.
I believe to achieve and ideal soil structure some things need to be understood. Terrestrial soils have different structures depending on what the soil is composed of, the amount of rain, forrest fires, and volcanic activity can all drastically change soil structure. A loose crumbly soil rich in nutrients that holds water well and allows for O2 to be evenly disturbed through the soil. So you have silts, clays, and sands bound together by organic matter and the clay in the soil. All of these variously sized sediments are evenly distributed throughout the organic matter. Clay and calcium help hold the sediments together in aggregates and are a big part of the texture of the soil.
I think a 50/50 mix of organic matter and sediments will produce soil mix similar to ideal terrestrial soils. My thinking is that an ideal terrestrial soil is no different that ideal aquatic soil.
I am personally using 25 pounds of green sand hoping the sand will be a mixture of roughly sand sized particles, five pound of montmorillonite clay that is very fine, five pounds of micronized Azomite because thats what I have. If I was going to buy more I would get the next size up so it would in theory take longer to dissolve.
If you want to see a list of trace minerals in Azomite and what they do google: "Primary Trace Minerals and Rare Earth Elements in Azomite" you will see what is claimed by the company to be in Azomite. Azomite is hydrated sodium calcium aluminosilicate from volcanic mineral deposits. Volcanic ash and sediments are full of minerals and trace elements. Azomite is not a clay of any kind.
The red clay powders you can get on eBay or anywhere for that matter do contain iron oxides not available to plants as iron. Iron oxide is a variably charged particle meaning it is covered with positive and negative sites that attract positive and negative anions and cations. It is actually moving micronutrients around in the soil with other particles of iron oxide.
Clay should make up about 10% of the total volume of a soil. Any more the soil can become too silty and because it is wet in a tank it will hold the soil together with the help of calcium in the lime I use to buffer the soil after everything is mixed in the soil. I don't think I can remember what I have read in learning about soils. If you have any questions that stick out to you I will find you an answer and try to explain it the best I can and Ill share the source wit you so you can check it out. I have some websites saved that might interest you explaing soil stucture and what and ideal soil aggregate looks like and what it is made of. As well as, anything I found interesting that applied to soil in any way that helped me put together a plan that is thought out.
I will link some websites I found helpful and if you have any questions shoot me a pm and I will get back to you.
A good read on someone preparing their soil substrate: How-To: Mineralized Soil Substrate, by Aaron Talbot - APC Library - Aquatic Plant Central
What makes a fertile soil:
Read section IV. Physical Properties of Soil:
Soils, Plant Nutrition and Nutrient Management:
I started a tread in the Low Tech forum titled "Soil Substrate Recipies Please Chime In" that will tell everything I plan to use and why. If you take the time to read through those sites and then read my recipe things will make a lot more sense.