Buffering Capacity of Soil

Buffering capacity is the soil’s ability to resist pH changes when acids or bases are added. It depends on reserve acidity (active, exchangeable, and residual acidity). Clayey soils with high organic matter have higher buffering capacity than sandy soils.

Factors Affecting Buffering Capacity

• Soil texture: Fine-textured soils have higher buffering capacity.
• Clay mineralogy: 2:1 type silicates increase buffering.
• Organic matter: Higher OM enhances buffering.

Importance of Buffering Capacity

• Stabilizes soil pH, preventing drastic changes harmful to plants and microbes.
• Determines liming requirements to neutralize acidity.

Types of Soil Acidity

• Active acidity: H⁺ ions in soil solution (measured by pH).
• Exchangeable acidity: H⁺ & Al³⁺ ions on soil colloids, released in salt solutions like KCl.
• Residual acidity: Bound H & Al in OM and clay, requiring liming for neutralization.

Causes of Soil Acidity

• Parent material: Acidic rocks (e.g., granite).
• Organic matter decomposition: Produces organic acids.
• Leaching in high rainfall areas: Removes bases like Ca²⁺, Mg²⁺.
• Acid rain: Sulfur & nitrogen oxides lower pH.
• Acidic fertilizers: NH₄⁺ fertilizers promote H⁺ release.
• Oxidation of sulfur/nitrogen: Produces H⁺ ions.
• Plant uptake of cations: Removes basic elements.

Effects of Soil Acidity

• Reduces nutrient availability (P, Ca, Mg).
• Increases toxicity of Al³⁺, Fe²⁺, Mn²⁺.
• Inhibits beneficial microbes (e.g., nitrogen-fixing bacteria).
• Affects soil structure and plant growth.