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Competency Area 5: Soil pH and Liming

PO 40. Describe how liming materials increase soil pH.

  1. Limestone is calcium carbonate and magnesium carbonate: CaCO3 and MgCO3
  2. The limestone dissolves in water to form carbonic acid (H2CO3) and calcium hydroxide (Ca(OH)2): CaCO3 + H2O ↔ H2CO3 + Ca(OH)2
  3. Carbonic acid is unstable and converts to carbon dioxide (CO2) and water; the CO2 gas escapes: H2CO3 ↔ CO2 + H2O
  4. The remaining calcium hydroxide dissociates: Ca(OH)2 ↔ Ca2+ + 2OH-
  5. The Ca2+ replaces 2H+ from the soil, increasing the soil base saturation
  6. The hydroxide anion (OH-) reacts with the soil acid cation (H+), forming water: OH- + H+ ↔ H2O