“The Ideal Soil v2.0” page 46 lists several CEC exchanges that happen: 2H+ for 1Ca++, or 2H+ for 1Mg++, or 1H+ for 1K+, or 1Mg++ for 1Ca++, or 2K+ for 1Ca++. The exchange of 2K+ for 1Ca++ would seem to indicate that Potassium has the stronger binding attraction over Calcium if I understand how the exchanges he listed work correctly.