Which amendment is used to decrease soil pH?

The chosen answer, sulfur, is indeed recognized for its ability to decrease soil pH, making soils more acidic. When sulfur is added to soil, it undergoes a chemical process, where it is oxidized by soil bacteria to form sulfuric acid. This acid effectively lowers the pH level of the soil, which is essential in situations where soil becomes too alkaline for certain crops or plants that thrive in more acidic conditions.

Understanding the properties of other options helps clarify their respective functions. For instance, potash is primarily a source of potassium, which is critical for plant growth but does not influence pH levels significantly. Calcite contains calcium carbonate, which is used to increase soil pH and correct acidity rather than reduce it. Bone meal is an organic fertilizer that provides phosphorus and calcium but also does not lower soil pH. Thus, sulfur stands out as the best choice for the purpose of decreasing soil pH effectively.