Which of the following is an example of a natural, organic fertilizer?

Bone meal is an excellent example of a natural, organic fertilizer. It is derived from ground animal bones, typically from cattle, and is rich in phosphorus and calcium, which are essential nutrients for plant growth. Being a byproduct of the meat industry, it is considered organic because it is not synthetically manufactured, but rather utilizes natural materials to enhance soil fertility and plant nutrition.

In contrast, urea, calcium nitrate, and potassium sulfate are synthetic or mineral-based fertilizers. Urea is an inorganic compound that supplies nitrogen but is artificially produced rather than sourced from natural organic materials. Calcium nitrate, also synthetic, combines calcium and nitrogen in a nitrate form, which is not derived from natural organic processes. Potassium sulfate provides potassium and sulfur and is typically mined or processed rather than being a natural organic product.

Thus, bone meal stands out as the only option that qualifies as a natural, organic fertilizer, making it the most suitable choice in this context.