Cation Exchange & Nutrient Availability
1️. Cation Saturation & Nutrient Release
- Higher % saturation of a cation = More available to plants.
Example:
- If 6 Cmol/kg Ca²⁺ is present in a soil with 8 Cmol/kg CEC (75% Ca saturation) → Ca is readily available.
- If the same 6 Cmol/kg Ca²⁺ is in a soil with 30 Cmol/kg CEC (20% Ca saturation) → Ca is less available.
2️. Influence of Complementary Adsorbed Cations
Adsorption Strength Order:
H⁺ > Al³⁺ > Ca²⁺ > Mg²⁺ > K⁺ = NH₄⁺ > Na⁺
Example:
- K⁺ is loosely held in acid soils (where H⁺ and Al³⁺ dominate), making it more available for plants but also more prone to leaching.
- In neutral to alkaline soils (where Ca²⁺ and Mg²⁺ dominate), K⁺ is held more tightly.
- High Ca levels can inhibit K⁺ uptake (nutrient antagonism).
3️. Effect of Colloidal Type
- Smectites (2:1 clays) hold Ca²⁺ tightly and require 70% base saturation before releasing it readily.
- Kaolinite (1:1 clay) releases Ca²⁺ more easily due to low charge density.