Which of the following amendments is commonly used to raise soil pH?

• A. Iron sulfate
• B. Limestone
• C. Aluminum sulfate
• D. Elemental sulfur

Answer: (B)

Raising soil pH comes from adding materials that neutralize acidity and supply base cations. Limestone fits this role because it’s mainly calcium carbonate. When applied, calcium carbonate neutralizes hydrogen ions in the soil solution and on exchange sites, forming water and carbon dioxide, and it releases calcium to displace acidic cations. Dolomitic limestone adds magnesium as well, which can help if magnesium is low. Liming effects are gradual and depend on soil testing to reach a target pH; overliming can raise pH too far and disrupt nutrient balance.

The other amendments listed either acidify soils or work differently: iron sulfate and aluminum sulfate introduce acidic components, lowering pH, while elemental sulfur must be oxidized by soil bacteria to sulfuric acid, also lowering pH. So limestone is the appropriate choice for increasing soil pH.