CEC and nitrate, phosphate
As I understand it, cation exchange capacity is the ability the substrate to bind positively charged ions and make them available to plant roots. After reading Positron's excellent explanation here, I've learned some ions are more easily attracted to the substrate:
However, major macronutrients nitrate and phosphate are negatively charged. Is CEC then non-applicable for these two nutrients then? A common concern with soil substrates is the depletion of nutrients, which if CEC worked for all nutrients, would be remedied by water column dosing. Yet if nitrates and phosphates aren't binded, is the depletion a bigger concern, especially for plants like HC and other carpeting plants that are recommended to be planted in a nutrient rich substrate?
Anion exchange capacity is a thing, but seems to only work in very low pH.
Thanks for any thoughts!