To raise soil pH and lower soil acidity, what is added to the soil?

• A. Sulfur
• B. Gypsum
• C. Compost
• D. Lime

Answer: (D)

Raising soil pH and reducing acidity is accomplished by adding lime. Lime, typically calcium carbonate or dolomitic lime, neutralizes the acidic hydrogen ions and exchangeable aluminum that keep soil pH low. This reaction gradually increases pH toward neutral and provides calcium (and magnesium with dolomitic lime), which also helps soil structure and root development. The effect is slow and depends on soil buffering, texture, and organic matter, so a soil test and follow-up applications are important.

Sulfur lowers soil pH by forming sulfuric acid, so it’s not used to raise pH. Gypsum supplies calcium and sulfur but doesn’t significantly raise pH, though it can improve structure and salt-related problems in some soils. Compost can modestly affect pH through organic matter decomposition, but it isn’t a reliable method for raising pH to neutral levels like lime is.