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

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Abstract
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+ (PBCK), when exchangeable K+ constitutes a minor portion of the CEC, depends on the magnitude of the soil CEC and the Gapon exchange selectivity coefficient (KG). This dependency is valid only if the Q/I plot is directly K‐(Ca + Mg) interaction dependent. Upon increasing the CEC and KG, PBCK increases since PBCK = CEC KG. At low KG values the CEC has a lesser influence on increasing the PBCK, and at low CEC values the KG has a smaller influence on the magnitude of the PBCK. The PBCK is also inversely related to soil K‐loading but the influence of K‐loading on the magnitude of PBCK, appears to be important only when exchangeable K+ represents a significant portion of the CEC. The influence of K‐loading on the magnitude of PBCK, 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.

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