Factors Affecting Cation Exchange Capacity (CEC) of Soil
CEC determines a soil’s ability to retain and supply nutrients to plants. Several factors influence CEC:
1️. Soil Texture
- Sandy soils have lower CEC due to low clay and organic matter.
- Clayey soils have higher CEC, especially 2:1 clays (Smectite) compared to 1:1 clays (Kaolinite).
CEC of different soils:
- Clay soils: Usually >30 meq/100g soil.
- Sandy soils: Range from 0–50 meq/100g soil.
2️. Soil pH
- Higher pH → Higher CEC (more negative charges develop).
- At low pH, only the permanent charges of 2:1 clays hold cations.
- At neutral to alkaline pH, more exchange sites become available, increasing CEC.
3️. Organic Matter (OM) Content
- More organic matter → Higher CEC.
- Organic matter contributes 2.0 Cmol/kg soil for every 1% humus.
4️. Type and Amount of Clay
- Smectite (2:1 clay) has higher CEC than Illite or Kaolinite (1:1 clay).
- Clay content directly affects the CEC of soil.
5️. Exchangeable Cations Present
- Soils in humid regions: More H⁺, Al³⁺ (acidic).
- Soils in dry regions: More Ca²⁺, Mg²⁺, Na⁺ (neutral to alkaline).
- Base saturation (percentage of CEC occupied by a particular cation) affects soil pH and nutrient availability.