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VT | The way I understand it, CEC is often back-calculated based on measurement of base cations, not by actually counting negative exchange sites. The way our tests are done, the CEC of our sandy soils will jump quite a bit after getting the pH from 5.7 up to 6.8. I assume that's because at the lower pH we have H+ occupying a lot of cation exchange sites, and the H+ is not being included in the calculation along with the Ca++, Mg++, K+, etc. Once we amend the pH up closer to neutral we see a big jump in CEC since those newly added mineral cations are occupying a lot of the sites previously occupied by the neutralized H+.
Perhaps Joel Gruver can chime in? | |
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