If soil has a high pH, which amendment should be added?

• A. Limestone
• B. Sodium Nitrate
• C. Ammonia
• D. Sulfur

Answer: (D)

When soil pH is high (alkaline), you want to add something acidic to bring the pH down. Elemental sulfur is a common and effective choice because soil microbes oxidize it to sulfuric acid, gradually increasing soil acidity and lowering the pH toward a more favorable range for many plants.

Limestone is the opposite: it adds calcium carbonate to neutral or raise acidity, used when soils are too acidic, not when they’re too alkaline. The other options—sodium nitrate and ammonia—are mainly nitrogen fertilizers and don’t serve as a deliberate pH-lowering amendment. They don’t reliably adjust high pH the way sulfur does.