Evaluation of Potassium Quantity‐Intensity Relationships by a Computer Model Employing the Gapon Equation

The influence of cation exchange selectivity coefficients on quantity‐intensity ( Q/I ) relationships of soil systems was evaluated by the Gapon equation. Computer simulations of potassium Q/I plots revealed that the linear potential buffering capacity for K + (PBC K ), when exchangeable K + constitutes a minor portion of the CEC, depends on the magnitude of the soil CEC and the Gapon exchange selectivity coefficient ( K G ). This dependency is valid only if the Q/I plot is directly K‐(Ca + Mg) interaction dependent. Upon increasing the CEC and K G , PBC K increases since PBC K = CEC K G . At low K G values the CEC has a lesser influence on increasing the PBC K , and at low CEC values the K G has a smaller influence on the magnitude of the PBC K . The PBC K is also inversely related to soil K‐loading but the influence of K‐loading on the magnitude of PBC K , appears to be important only when exchangeable K + represents a significant portion of the CEC. The influence of K‐loading on the magnitude of PBC K , however, appears to be considerable only at K‐loading values much higher from those encountered in most agricultural soils. These findings are supported by data available in the literature.