Selenium and Cobalt

[nuttiest]

Is anyone sourcing these, and if so what form do you use?

 

[Shibui]

Any decent complete fertiliser should already have adequate micro nutrients so no need to find each one separately.

 

[nuttiest]

Maybe in Australia... here there are no micronutrient supplements or fertilizers that contain cobalt, selenium or silica.
Silica need would different depending on substrate.

 

[Glaucus]

Selenium, cobalt and silica are not essential micronutrients for plants. Plants cannot be deficient in them. Additionally, selenium and cobalt hang around in trace amounts in tap water and soils. And silica is abundant in soils, just not bioavailable. Which is why generally plants have no use for them. Whatever is the limiting factor on your plants growth or health, it isn't any of these.

 

[nuttiest]

Additionally, selenium and cobalt hang around in trace amounts in tap water and soils

and I get the reason manufacturers cannot do this but it is maybe not just a toxicity concern. Encapsulation in prills would be difficult given the small amounts, and cobalt is expensive to add.

 

[JeffS73]

Hydroponics companies can sell you Silicon that is bio available, cobalt is a heavy metal, generally toxic. Maybe get 0.001g of a gram from a potter?

 

[nuttiest]

Silicon that is bio available

I see they say that diatomaceous earth is the most effective way to add silica, so that's easy enough, but because getting doses of other 2 needs to be micrograms, I may do the selenium that are already measured out in supplement form.

I need to make clear this is a ONE time thing - not even a yearly supplement.

Now I answered my own question about why they are not in fertilizers

 

[Glaucus]

If you buy silica you may indeed get diatomaceous earth that is ground down into a powder. It is not bioavailable. If you want bioavailable silica, get a product like Yara Actisil. The best bioavailable form is orthosilicic acid.

It will be hard for a manufacturer to give you soil or fertilizer that is completely pure of any trace amounts of selenium or cobalt.
Many bacteria need cobalt, including bacteria that fix nitrogen in the soil.
If there would be no bioavailable cobalt in your soil, or your fertilizer, or anything, no bacteria or fungus would grow on it. It would stay completely sterile even with plenty of macronutrients, warmth and moisture.
So if you are worried about a lack of cobalt, then take a petri dish. And add some stuff that contains no cobalt. Like kitchen sugar, starch, and make a nice layer of that stuff. Then sprinkle your fertilizer on top of that. Make sure it is very moist. Put the cover on that petri dish And incubate at 30C. Then check in 5 days. If there is zero cobalt, there would be zero growth of bacteria or fungi.

 

[nuttiest]

If you buy silica you may indeed get diatomaceous earth that is ground down into a powder. It is not bioavailable. If you want bioavailable silica, get a product like Yara Actisil. The best bioavailable form is orthosilicic acid.

nice - thank you

It will be hard for a manufacturer to give you soil or fertilizer that is completely pure of any trace amounts of selenium or cobalt

I realize there is some contained in copper, but not as much as 'reccommeded' which is kind of only for soy growers maybe.

So if you are worried about a lack of cobalt, then take a petri dish. And add some stuff that contains no cobalt. Like kitchen sugar, starch, and make a nice layer of that stuff. Then sprinkle your fertilizer on top of that. Make sure it is very moist. Put the cover on that petri dish And incubate at 30C. Then check in 5 days. If there is zero cobalt, there would be zero growth of bacteria or fungi.

Love it - all anyone needs is at the vitamin store and science supply.
Thanks, Glaucus.

 

[Glaucus]

Well, the point here was that selenium and cobalt are needed in nanomolar or even picomolar amounts. Where normal nutrients are needed in micromolar and more common essential mineral elements in micromolar amounts. Meaning it is not so easy to in a lab setup, starve plants, bacteria, fungi from those micronutrients. Of course one can do it. But any normal everyday item. Like a bag of sugar. Or a bucket of sand. Or tap water. It will all contain these micronutrients. So historically, for some of these it was just very hard to demonstrate a deficiency in the lab. As it was hard to rule out any 'contamination', which would then fail in starving the plant of this nutrient.


A reference work on all of this is Marschner's mineral nutrition of higher plants. There is science done on adding additional Cobalt, silica and selenium. But these are among the bottom of the barrel nutrients in terms of what one as a plant grower needs to add to improve health.

But true, you could buy vitamin B12 and feed that to your plants.