That makes sense and I agree calculating CEC from milliequivalents of K, Mg, Ca, Na, H probably isn’t a great way to reflect the ‘inherent’ capacity of the soil to sorb cations. The different CEC you are seeing in your case might be due to the different pH of the two soils. From Ward Labs soil testing guide: In most soils, CEC increases with pH. At very low pH levels (< 5.0), hydrogen (and perhaps aluminum) ions are held so tightly that they effectively resist replacement, resulting in a relatively lower CEC than at high pH values. As pH increases, hydrogen is ionized and is thus replaceable, releasing additional sites on the clay (or humus) particles.