Originally Posted by paradoxlost
So the way the CEC test works is this:
You flood the CEC sites with NH4+. Than you take a solution with a known concentration of K+ with a volume greater than the volume of the soil porosity. Than you flood the soil with a solvent and measure the concentration of K+ that were held on cation exchange sites. This concentration will tell you the amount of cations held per unit volume of soil.
This is the basic jist of the ammonia CEC determination. Obviously there is a little more too it, it's been a while since I have done this technique.
The limitations of this are with alkaline soils and saline soils, as salts will start to form ionic bonds which have the same effect as CEC, but are technically not part of CEC. Maybe the spectroscopy technique might have an accuracy issue. If you're running Atomic Adsorption Spectroscopy, versus something like an Induced Couple Plasma.
Idk what spectrum does btw as far as spectroscopy. But probably Atomic Adsorption. That is the most cost effective, and accurate enough for agriculture's purpose.
Thanks for reply, I do understand how the test works. My point was more about the quality of the people & processes along the way. How you take that soil sample, where, how many spots, how it's sifted, mixed and so on. The person in the lab, how detailed are they, how detailed is the labs process, how much pride do the people take in their jobs doing that work etc etc etc... Samples are also taken at a point in time - I was more trying to say it's has endless limitations but also offers invaluable detail.
My native around here in spots is > 12% OM, 40% is certainly a lot for OM but not unheard of.
reading this thread it just feels at times that some think their going to become a great farmer if only they get that perfect soil test result - I can't stress how wrong this is and IMO, leads many down the wrong rabbit hole...
Understanding is King, test results are simply one piece to that puzzle