Which of the following is a slow-release phosphorus source effective in acidic soils?

Rock phosphate is considered a slow-release phosphorus source that is particularly effective in acidic soils. In such environments, the solubility of rock phosphate increases, making phosphorus more available to plants over time. The apatite mineral contained in rock phosphate does not dissolve quickly, but it gradually releases phosphorus as it reacts with soil acids, which helps to maintain soil phosphorus levels beneficial for plant growth.

Compost, while it can contribute nutrients including phosphorus, does not specifically provide a slow-release phosphorus source tailored for acidic soils like rock phosphate does. Superphosphate, on the other hand, is a more chemically active form of phosphorus designed for immediate availability, rather than a slow-release option. Bone meal can act as a phosphorus source as well, but it is generally considered to have a faster breakdown than rock phosphate and may not be as effective in acidic soils when considering the long-term release of phosphorus. Therefore, rock phosphate stands out as the ideal choice in this question.