Effects of Lime on Acid Soils

A. Direct Effects

Liming reduces the solubility and toxicity of Al³⁺ and Mn⁴⁺, which can cause:

• Inhibition of root cell division.
• Reduced root respiration.
• Increased cell wall rigidity.
• Interference with enzyme activity.
• Impaired uptake of nutrients like Ca, Mg, and P.
• Root membrane damage below pH 4.5, affecting beneficial microorganisms.

B. Indirect Effects

a. Phosphorus Availability

• At low pH, P is fixed by Al, Fe, and Mn, forming insoluble compounds.
• Liming increases pH, inactivating these metals and making P more available (best at pH 6.5–7.5).
• Excessive liming can reduce P availability due to precipitation as CaPO₄ or MgPO₄.

b. Micronutrient Availability

• All micronutrients (except Mo) are more available at low pH.
• Mo becomes more available at higher pH due to liming.

c. Nitrification

• Increased nitrification as NH₄⁺ is converted to NO₃⁻ at pH 6.5–7, benefiting plant growth.

d. Nitrogen Fixation

• Rhizobium activity and N₂ fixation improve at pH ~6.5, enhancing legume growth.

e. Disease Control

• Club root in Cole crops is reduced by raising pH.
• Potato scab incidence increases if pH exceeds 8.