All I really know about cobalt is that way back in ceramics class in high school, we used it in glazes for the color blue (when fired). OH ya, it wasn't cheep either (but don't remember any prices). And I have never seen it listed as a trace (or any) element (essential or not) in a hydroponic nutrient. Although I have read a little about Silicon as being a beneficial plant nutrient (not essential though).

Thanks Homehydro,
I found it. The source States;
"COBALT (Co) - a constituent of vitamin B-12 and required for the fixation of nitrogen and DNA synthesis".
"Deficiency - causes pernicious anemia (lack of vitamin B-12) and improper nitrogen assimilation".
"Toxicity - all but smallest amount causes quick wilt and death".
OH ya, The source sells it in the form of cobalt nitrate [Co(NO3)2 + 6H2O] to the tune of $49.95 per pound (1 Lb. minimum) plus S&H. But the good news is that their complete nutrients incorporate the proper micro dose. Although I believe they formulate good nutrient products at a reasonable price I'm beginning to Kind of doubt that cobalt is essential, required, or beneficial. Maybe its not even plant digestible in this form.
I've read a little on silicon also, and that it protects the roots from fungi. Would that defeat the use of Mycorrhizae (beneficial fungi)? How beneficial is Mycorrhizae? I understand that it's organic and I rather not go that root if it will create problems Or if it lacks results.

I did a search for those exact quotes and it only came back with one match.

http://www.marijuanapassion.com/forum/showthread.php/7536-Mineral-Elements?p=61299&viewfull=1

In the beginning of that post it mentions that the information was out of the "ECO Enterprises" catalog. I haven't checked into that catalog. But I would always recommend to be weary of just believing any sales pitch. With that said, I am not suggesting that there's not any validity to Cobalt as a nutrient, just that one should consider the source of the information. I also did another search for "Cobalt+hydroponics" (with the quotes) then narrowed it to .edu websites under advanced search. Here's the search result list: Cobalt hydroponics site:.edu

I did find this statement (under section Nutrient Solution Recipes):
"Certain plant species may need others for good growth: Silica (Si), Aluminum (Al), Cobalt (Co), Vanadium (V), and Selenium (Se)."

From, http://ag.arizona.edu/hydroponictomatoes/nutritio.htm
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Also these statement (under section titled "OTHER NUTRIENTS: Elements that have been found in plant tissue and are most
likely required by some plants in some amounts for growth.")

"2. Silicon: May be involved in cellulose formation and carbohydrate metabolism. Seems to protect against insects, diseases and many environmental stresses. Beneficial for C4 and CAM plants.
3. Cobalt: Required by nitrogen fixing bacteria in legume plants."

From, PLANT NUTRITION AND NUTRITIONAL DISORDERS (also a arizona.edu website)
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Also these statements:

"To be considered an essential element:
1. must be required for completion of life cycle
2. must be involved in some aspect of metabolism as part of a molecule, enzyme cofactor, ion for water
balance, etc.
3. no other element can substitute for it"

"Other elements are required by particular groups of plants. In some cases, there is not an absolute
requirement for the element. These are called beneficial elements:
Na (sodium): required by CAM plants and C4 plants
Si (silica): part of the cell wall of a number of land plants, including Equisetum, tomato, and many
grasses
Co (cobalt): needed the Rhizobium symbionts of legumes for nitrogen fixation"

From page two, section titled Mineral Nutrition: Mineral Nutrition (from Weber State University, Ogden, Utah)

So it would appear that cobalt is needed by bacteria and not the plant per se. I would assume that hydroponically grown plants don't fix N the same as soil grown where the process is anaerobic - oxygen kills the bacteria that use the cobalt to fix nitrogen.

Yes, I got the Quote from the Eco catalog page 10. They fail to explain that it is required for organic pea/bean inoculation and does absolutely nothing for maters in a sterile hydro solution. I didn't think it smelled right. Thanks for all the legitimate reputable links and the time it took to research it.
~Ken~

Zathras,
You posted while I was still typing. Yes, the Rhizobium Symbionts (a beneficial bacteria) need traces of cobalt to grow and feed nitrogen to the roots of legumes. Some example of legumes are: Peas, Beans, and I think vetches and clovers. This combination is often used as a cover crop to grow what is called a Green Manure to provide nitrogen in organic soil gardening. Tilling in this crop works great for building up nitrogen in an outdoor organic Soil tomato garden.
However, Tomato plants do not require beneficial bacteria to fix their nitrogen and the last time I checked most of us do not rotate crops and till dead plants into our reservoirs to build up our nutrient solutions. Was this explanation helpful?

Just thought I I would add this link: Nutrients: Beyond Macros and Micros

It is a commercial website, but the article was written Dr. Lynette Morgan is an internationally recognized hydroponics consultant, researcher, and the author. I am still wanting to get her book on "Hydroponic Strawberry Production"

homehydro,
Great article. It pretty much confirms that my .242 EC (122 ppm) well water may have some benefits over my a/c condensate as I Previously suspected. Now if I could get a complete analysis regarding Calcium, Iron, magnesium and sulfur content to compensate for, it should be safe to assume that most of these micro/trace minerals would be Included in sufficient quantity.
Thanks again.
Ken

Homehydro,
Daniel put together a good read regarding cobalt.
Its at allhydroponics.blogspot.com/2010/08/cobalt-in-hydroponics-better-or-worse.html
It explains your findings quite well.
Thanks Daniel,
Ken

Thanks hardclay7a,
I'll give it a read. I bookmarked it. It also looks like there's an article about silicon too, I'll give that one a read also.