Overuse of which nutrient can lead to increased acidity in soils?

The overuse of sulfur can lead to increased acidity in soils due to its chemical properties and how it reacts in the soil ecosystem. When sulfur is applied to the soil, it undergoes oxidation and is converted to sulfate, which can release hydrogen ions into the soil solution, thereby lowering the soil pH and increasing acidity. This effect becomes more pronounced when sulfur is applied in large quantities, as it can significantly alter the ion balance within the soil.

In contrast, nitrogen is crucial for plant growth but does not directly cause soil acidity in the same way sulfur does. Similarly, phosphorus is essential for root development and energy transfer in plants, but it typically remains neutral in terms of pH effect. Potassium, while vital for various physiological functions in plants, also does not contribute to soil acidity when used appropriately. Hence, sulfur is the specific nutrient that, when overapplied, can lead to increased acidity, supporting the correctness of this answer.