Which statement about lime and sulfur as soil pH amendments is true?

• A. Lime raises pH and sulfur lowers pH.
• B. Lime lowers pH and sulfur raises pH.
• C. Both lime and sulfur raise pH.
• D. Neither lime nor sulfur affect pH.

Answer: (A)

Understanding how lime and sulfur modify soil pH helps you see why this statement is true. Lime, typically calcium carbonate, neutralizes acidity in the soil solution by reacting with hydrogen ions, which raises the pH and makes the soil less acidic. Sulfur works the opposite: when added as elemental sulfur, soil bacteria oxidize it to sulfuric acid, increasing hydrogen ion concentration and lowering the pH. This is why lime is used to raise pH on acidic soils, while sulfur is used to lower pH on alkaline soils. The other options don’t fit because lime does not lower pH, and sulfur does not raise pH (in practice, sulfur’s effect is to acidify, not alkalinize).