If you want a more sophisticated protocol that involves using a Brix meter and biological soil testing from Logan labs, go to the website of the Real Food Campaign.
First I want you to know you strike me as a sincere person and I don't think you're a scammer or spammer in any way. In fact, you remind me of my late grandfather who was a natural healer. He had a gift for healing, sort of a cross between a chiropractor and nutritionist, although he never had much schooling. But God bless him, he also bought into every nutrition scheme, including soil nutrition, that sounded good and was probably taken a few times. My mom still buys into many such things and no amount of real science will convince her otherwise.
Now that we're done with the nice-ities (smile), I didn't know what a Brix meter was so I looked it up. That is about as unsophisticated as one could hope to get. That doesn't mean it can't be useful. It's comparable to a TDS (total dissolved solids) meter that I've used to screen well water. The operative word here is screen. This is not the same as analyze.
From the web site you recommended, near bottom of page:
"Also remember that many other substances can falsely indicate "brix" readings"http://realfoodcampaign.org/content/brix
A Brix is not a serious analytical tool. I didn't see anything about biological testing on the web site but maybe I missed it.
EDIT: I checked the Logan Labs web site and didn't see anything about biological testing there either. Again, maybe I missed it.
As I said in an earlier post, I can use the lab at which I am employed on a limited basis. I already have the soil remineraliztion products Sea90 and Azomite. As soon as the ECOMIN gets in I will bring samples to the lab and put them on an XRF (X-ray fluorescence) spectrometer. I will also take a soil sample from my garden just for giggles. This will detect pretty much every element from sodium on up. So copper, potassium, gold, etc., no problem. As my XRF is configured it does not provide structural information, only presence of elements. It cannot the the lighter elements such as nitrogen, oxygen, carbon, etc. Thus it cannot detect nitrate (NO3) or carbonate (CO3) as these are lighter and also require structural information.
I also have access to two ICs (ion chromatographs) with mass spectrometer detector, one configured for anions and the other for cations. These can readily detect nitrate but I have never attempted carbonate. My guess is the anion IC will pick it up but I'll have to run a standard to know for sure. This is not a problem.
I also have access to a few other instruments but the XRF alone will probably tell me what I want to know, which is the presence of trace elements.