Potassium silicate is soluble and immediately plant available at 5-6.5 pH range. Wollastonite, zeolite, diatomaceous earth, and flowable Gypsum may be suspendable but not soluble. This makes them candidates for media amendment, but not nutrient solutions.
EDIT: We can add azomite, lignite and Leonardite to that list, but heavy metal content they contain and pH availability for their benefits are a whole different discussion with these materials.
Wollastonite is plant available fairly quickly (hours to days based on bugbees study I attached) and last for months when amended in the substrate. Woll also is great as a foliar to mitigate PM. Wollastonite is set and forget and I suspect that’s the reason sunshine#4 puts it in their loose substrates. I attached some studies vansil provided. Correct me if I’m wrong but potassium silicate or silicates period are NOT available to plants until it’s broken down by bacteria after weeks and months to give us monosilicic acid. Hence the reason for earlier post of available silicic acid mixtures right?
Bioavailable Silicon_ Release Rate from Additives & Substrates (1) (14).pdf (1.5 MB)
VANSIL_Ag_Uses (6) (1).pdf (167.8 KB)
I have a 25lb bucket of agsil 16h sitting up because I haven’t used it this year really, the results from the woll we’re night and day for us. Visually the plants were turgid in less time. It seemed to me that wolly did in about 10 days what agsil took 3-4 weeks to do.
I have been searching my drive and bookmarks and I can’t find it but there was a study done and it showed plants taking 4weeks to accumulate enough si in the range we are looking for with our plants.
What I’m trying to get at is, how long does it take for potassium silicate to break down into silicic acid then? If potassium silicate is immediately plant available then why are we looking to use monosilicic acids?
I’m coming from a place of wanting more knowledge. This is peaceful from my side everyone.
The Effects of Foliar Sprays with Different Silicon Compounds.pdf (868.4 KB)
fpls-08-01061.pdf (1.8 MB)
You’re correct that monosilicic acid is the only form that is bioavailable. However, when in solution at the pH range mentioned, potassium silicate will immediately begin to depolymerize, creating a usable amount of silicic acid.
Higher concentrations and stability.
silicic acid = monosilicic acid = orthosilicic acid = PAS (plant avabile silicon); they are different names for the same thing.
Maybe this paper will be helpful:
It seems like you may think potassium silicate is the same thing as silicate sand or another silicate mineral. While it’s really like table salt, meaning it instantly dissolves into the water. Potassium silicate doesn’t “break down” into silicic acid when dissolved in water under appropriate conditions: the potassium and silicate immediately separate when they dissolve, and the silicates convert into silicic acid under the correct conditions.
The conversion of silicates from the salt (potassium silicate) into silicic acid is close to instantaneous as it dissolves into water (see the assumptions I wrote to @WhereAreTheStones making that statement true). I’m not sure anyone knows exactly how long it takes experimentally, but theoretically is a different matter. I would hazard guessing in the order of milliseconds to seconds. But I would imagine that as the silicon concentration increases in solution, the conversion rate of the silicates to silicic acid slows. And if you add too much silicon (>47 mg/L) at our pH range (5.5-6.5) to purified water, or you add ⪆10 m/gL silicon to a nutrient solution has that higher EC, the silicates will polymerize and/or precipitate.
@danielfp would be the one to ask for greater specifics regarding conversion rate and efficiency.
But, it’s safe to say if you’re following the assumptions I wrote below, the silicates will immediately convert to silicic acid under the right conditions.
For another example, suppose you want to make a stock solution of potassium silicate to mix into your nutrient soution. In that case, you first need to increase the purified water pH to 11 using potassium hydroxide, then dissolve the potassium silicate providing at most 421 mg/L Si, and finally top up to your target volume. Ensuring the final pH is at least 11.3.
Silicic acid = monosilicic acid. What we’re trying to do is stabilize the silicic acid. We’re trying to delay the polymerization of silicic acid by ions in solution, pH, oxidation(?), and time. So the silicic acid stays as silicic acid for as long as possible.
Think about it like this: We’re trying to surround (encapsulate) silicic acid with a protective barrier so it’s isolated and doesn’t interact with the other ‘stuff’ in the solution.
I could be mistaken, but, IIRC, when preparing a fresh nutrient solution, silicates from potassium silicate don’t depolymerize before converting into silicic acid because they’re not polymerized, assuming:
Polymerization occurs in existing/older nutrient solutions. Including when adding-back Si, espeically when higher Si rates are applied (~15-45 mg/L).
pH 11.3 Enhances the Solubility of Potassium Silicate for Liquid (1).pdf (1.0 MB)
Much appreciated everyone. All the information I had and knew was from years previous. Found that bugbee study from 2021, I attached it. It basically saying the same thing about mixing at a pH of 11.3 or higher.
Better solubility and much easier on your dosers. It seems we have been mixing agsil incorrectly for years now. I never ran ro or deionized water system before as I have been blessed with .2 ec at out last few locations.
Does anyone have suggestions on either system for small commercial settings?
@crowngruv that article has a good section on Reservoir turbidity. If used as pH down, the amount of phosphoric acid to adjust from 11.3 pH will require modification of your nutrient formulation.
When they started discussing turbidity in the article I attached I immediately read your post about it afterwards.
My next question is as it pertains to lowering our ph I have always used phosphoric acid. Would sulfuric acid have less effects on the nutrient formulation?
Also why does bugbee use nitric acid and neither of the above mentioned?
Utah Hydroponic Solutions.pdf (733.4 KB)
@crowngruv Bruce uses nitric acid with ammonium nitrate because in recirculating systems the plants will deplete solutions of N first and do require N replenishment, so the pH down serves a double purpose, it replenishes N as nitrate and also shifts ammonium balance to reduce future pH excursions towards the upside. In a run-to-waste system, where you only want to adjust pH for a single irrigation, you can use phosphoric, nitric or sulfuric, provided you adjust your formula to account for each addition.
Sulfuric is the best one to use because sulfate additions hardly affect plants, plus - since this is the strongest acid - it requires the lowest addition on a molar basis. In cannabis it is also important to control N and P as exactly as possible, so using sulfuric acid allows you to adjust pH without affecting your micro nutrient profile.
Here are some clarifications about Si in solution, for those interested:
Plants not only uptake monosilicic acid. They can uptake dimers and even substantial oligomers of silicic acid. Even silica nanoparticles of sizes of up to 20nm have been shown to be taken up by plants. It is safe to say that any form of molybdenum reactive silicon can be taken up by plants.
When basic silicates (potassium or sodium) dissolve at high pH, the silicon is mostly present as oligomers of silicate, not monomers. These oligomers are more stable at basic pH because of how strongly negatively charged they are (so they repel each other). At low concentration (lower than ~20 ppm) they break to the point where they are present mostly as monomer silicate, which turns into silicic acid when the pH is lowered. However they need to be diluted before the pH is brought down, if you lower the pH of a concentrated Si solution, the oligomers will never break and will just polymerize (they lose negative charge and can react with each other to form larger chains). This is why it is so important to add silicates first, then nutrients, then correct pH.
Once you have silicic acid at low concentration (<20 ppm) at neutral or even slightly acidic pH, it seems to be stable for weeks. I tested this hypothesis with one of Bruce’s students, Si from both acidic and basic sources of silicon, added to a pH 6 buffer (citric acid/citrate with an osmotic strength equivalent to a regular nutrient solution with an EC of around 2mS/cm) was stable for 5 weeks with no change in concentration we could tell. Whether it came from acid stabilized Si or base, made no difference. The amount of Mo reactive silicon remained the same.
Given the experimental results that I’ve seen, I would say that an acid stabilized Si source - once taken to pH 6 - is chemically as stable as Si from a basic source that has been taken to the same pH. Stabilizing agents seem to play no role once they are diluted so much. With these results, I see no reason why an acid stabilized Si source would be more desirable.
It is likely that beneficial effects that are unique to the Si stabilized forms in foliar tests are inherent to the effect of the stabilizing agents themselves on the plants. But not caused by the Si itself. At high dilutions of Si with highly dilute stabilizing agents, the Si forms cannot be told apart when acid or base are used, Si NMR also seems to support this conclusion.
In the case of Wollastonite, it is safe to say that some Si is available to plants probably seconds after it is put in a solution – which is when we see the first quantifiable amounts of Mo reactive Si. Microbe interactions might make things happen faster for some sources, but Wollastonite and other Ca silicates are quite highly soluble (compared to other silicates which don’t dissolve at all). If you add Wollastonite as an amendment, plants will uptake Si on every irrigation until the amendment runs out.
Bruce’s results show that an addition of around 1-3g/L of Wollastonite will lead to 5-10ppm of Si to become available per irrigation. Assuming complete plant uptake, you are likely to lose around 40mg/L of Wollastonite per irrigation, which means, 1g/L is likely to last you around 25 irrigation events. Adding more Wollastonite won’t lead to higher Si concentration per irrigation, it would just last longer or be more homogeneously distributed in the media (fewer pockets of high/low concentration). For a full crop cycle 3g/L of wollastonite is likely to be more than enough (75 irrigation events).
I have tested the above with clients and we get the same tissue concentrations of Si as we got with a 20ppm of Si supplementation from potassium silicate with 10-30g/L of Wollastonite (I haven’t tried less, we just wanted to be overly safe).
First thank you for the detailed response. My fear had always been using too much wollastonite as I never did any tissue samples. I just saw that it worked visually and stopped anything in the coco from growing like nates, thrips etc.
Whats interesting was many months back I spoke with Mackenzie Jones in email about her study with Bruce. There were 2 things she addressed for me which were a concern.
wollastonite r&d 10-15% substrate
You have confirmed and clarified a lot for me, thank you. I had to read that over a few times but its clicking.
Did some math I would be at .08 cents per pot of wollastonite for an entire 3 month run and agsil 16H @ 9.10 per gallon (7.8% rtu formula) I would be at .90 cents for a 3 month run per pot.
Something I don’t comprehend fully is when I was looking at the spec sheet for wollastonite I saw that a 10% slurry would net you a ph of 10-11. Based on Bugbees chart the solubility of si increased after about a ph of 10, so would one then be able to simply ph down this solution and you’re ready to use based off what you stated above? Or would you still need ro/deionize - koh - CaSi - acid of choice? And am I not sure on the correct vernacular or terms but am I right to assume the calcium carbonate in tap water would cause precipitation with the wollastonite in solution?
So there are a couple of important things here.
A slurry of wollastonite at 10% that is allowed to reach steady state - stirred until silicate no longer dissolves - will likely have an Si concentration close to 1g/L (1000 ppm of Si), at a pH of around 10-11. This will however take quite a long time to achieve (likely a few days). If you did this with tap water (containing Ca) it will likely be a bit lower, because of the common ion effect.
If you filtered it - to remove the solid - and lowered its pH, it would precipitate out a lot of silicon as silica, because the Si concentration would be too high and it would polymerize. You do not want to use Wollastonite by creating slurries that are allowed to reach equilibrium with water. This takes a long time and is ineffective.
It is also difficult to predict what concentration of Si will be reached with a Wollastonite slurry if you do not allow equilibrium to be reached. Depending on temperature, pH ,ionic composition of the water and time, it might be anything between 0 and its equilibrium concentration.
However, when you irrigate, Wollastonite never reaches the steady state, it just dissolves while there is enough water, then it stops dissolving. Since it dissolves so slowly, it barely dissolves and barely increases the pH. Since the nutrient solution has significant buffering capacity and also contains substantial amounts of Ca, it hinders the solubility of the Wollastonite, on top of its already very sluggish dissolution kinetics at pH 6 (sluggish, but enough to give you 5-10ppm of Mo reactive Si per irrigation, which is perfect).
It is critical to consider here that we are not achieving the steady state equilibrium with Wollastonite in media, we are just allowing it to start its dissolution process so that enough silicon is released such that plants can use it. It happens to have just the right dissolution kinetics for that.
When in media the plant roots and nutrient solution help regulate the release and process because the timing of water exposure to the Wollastonite is dependent on the root uptake of water. If you try to do a slurry and water that, it is entirely up to you and a much messier deal (because you would need to filter that as well, control time, temperature, adjust pH, etc).
Ok so that answers that.
Our best options are wollastonite in the media or filtered water, ph up to 11.3+, si, then ph down to your working solution.
So from what I understand from that very good explanation, using peg sorvitol etc, as stabilizers, is not necessary, simply, pH below 1-2 sulfuric acid and stock solution mother is ready?
Thank you DF for your contribution.
Sadly, no. It’s best to use the basic (pH) stock solution I described (see the report liked by @crowngruv) if you don’t want to use stabilizers. Or use direct addition (don’t make a stock solution) if you’re running a small grow.
I may have misread your post, but wollastonite isn’t the best option for fertigation with Si. The best option is potassium silicate. How you prepare the silicate stock solution depends upon your goals.
Currently, there isn’t enough information, either way, to say if a stabilized silicic acid stock solution is beneficial compared to adding silicate (direct addition or from a basic stock solution) for irrigation. Let alone for the many different substrates and hydroponic methods growers use. Plus, when complexing silicic acid with carnitine, the stabilization of silicic acid may carry over when diluted into the nutrient solution to some degree.
When using a basic (pH) stock solution of Si, whether you need to reduce or increase the pH of the nutrient solution depends upon the solution preparation. For example, using RO water and injectors or dosers with an A and B stock solution method, where at least one of the stocks is at pH 3.0-4.0, the basic silicate stock solution serves the dual purpose of adding Si and increasing solution pH. When formulating and mixing nutrients in-house, it’s possible to design the stock solutions so the basic silicate stock solution is the only pH adjustment.
The same holds for foliar. There isn’t enough evidence to make a definitive claim for the superior Si source. Even though there is evidence that stabilized silicic acid may be better than silicate. High-quality foliar fertilization studies are the exception, not the rule, because researchers typically don’t optimize foliar solutions for concentration gradient, pH, adjuvants (including surfactants), timing, environmental conditions, droplet size, etc. Let alone optimize the controls they apply.
And plant cuticles aren’t identical between all species or even a single leaf; for example, the cuticles of some plant species have a crystalline nature while others do not. There are differences in leaf absorption of water and aqueous solutes in rate, cuticle pathway tortuosity, uptake, presence of various epidermal structures (like trichomes), stomatal density and size, etc. Science has much to learn about the mechanisms of foliar uptake by plants.
You do need stabilizers at acidic pH. Although silicic acid is more stable at highly acidic pH, it will still polymerize readily at high concentrations (>100ppm). If you prepare a 1% Si solution at pH <1.5, you absolutely need stabilizing agents or it will just polymerize and form silica gel.
Given that the forms of silicon are basically equivalent when you dilute them and put them at pH 6 (otherwise the Si-NMR spectra would look different). It is safe to say that, at least regarding Si, it makes no difference whether you come from a basic silicate concentrate or an acid-stabilized silicic acid concentrate (at least with Si in the 10-20 ppm range in the final solution).
Any difference must therefore be exclusively due to the effects of the stabilizing agents on the plants. Many of these - carnitine, glycerol, boron, molybdenum - are expected to be taken up by plants and play a role in plant metabolism.
We do need studies with proper controls, where a basic Si with the same stabilizing agents added is compared with an acidic Si with the stabilizing agents and with a solution that just contains the stabilizing agents. We should see absolutely no difference between both Si treatments and probably an improvement of the stabilizing agent control over a control with just water being sprayed.
If I have a 1% solution without stabilizers and without the formation of silica gel and it is diluted to 20ppm, it will go from oligomer to monomers and finally silicic acid? as it would happen in a basic solution at pH11.
From my study of the chemistry of silicates - both from published data and experiments done with others - it seems clear that Silicon containing polymers and oligomers only break up at very basic pH values (>11). This is why basic solutions can dissolve SiO2, but acid solutions cannot (with the exception of fluoride containing acid solutions).
If you have a 1% solution in acid pH, whatever its makeup is will remain as-is or polymerize further once you bring it to 5-7 pH. Even if you dilute it, oligomers will not break (this only happens at basic pH).
Thank you for your contributions to learning about the science of monosilicon acid. danielfp , Ralf
I was looking about DMSO and its applications and I found this patent, where if I understand correctly it uses DMSO or MSM as the first stabilizer and propylene glycol, etc as the second stabilizer, it also mentions that maltose, dextrose, sucrose, sorbitol, xylitol, glucose, dextran, no They are good stabilizers.
I await your opinions, the patent covers colloidal silicon, I suppose that is not so important.
excuse my english by google
Did you ever do the side-by-side comparison on it?