An exchange occur in the root zone whenever a plant root accesses a cation from the clay colloid. The plant may take some calcium, for example but when it does so, an electrical balancing act is performed. If the plant takes
If you have medium clay soil with a CEC of 20 to 30, then you have much higher storage capacity and less need to spoon feed. As long as fuel tank is not empty, these soils can deliver nutrition for extended periods. These are the soils that respond well to cation balancing strategies, where we try to achieve a cation balance involving 68% Calcium, 12% Magnesium, 3-5% potassium and less that 1.5% sodium on the clay colloid. The original research conducted by Dr. William Albrecht applied specifically to these types of soil.
However, we often find that playing the precise numbers game in very heavy soils is not always productive. These soils (with a CEC of 30-70) have such a large storage capacity that their need for extra inputs should always be confirmed with a leaf test. For example if you have 7000 ppm of Calcium on your soil test, that often can be enough. Always leaf test to see if the plant is accessing enough calcium before embarking on liming or Gypsum program that may not be necessary. If the leaf levels of calcium are good there is simply no need to play number game.