Which of the following is an example of an organic fertilizer?

• A. Urea
• B. Ammonium sulfate
• C. Potassium nitrate
• D. Worm casting

Answer: (D)

Organic fertilizers come from natural sources of organic matter and support soil life as well as the plants. Worm casting fits this because it’s produced by earthworms digesting organic waste, adding nutrients in organic form along with humus and beneficial microorganisms. This improves soil structure, water retention, and microbial activity, and nutrients are released slowly as the organic matter breaks down, reducing leaching and burn risk. The other options are synthetic inorganic fertilizers: urea, ammonium sulfate, and potassium nitrate all provide nutrients in readily available forms and mainly boost plant nutrition directly without enhancing soil organic matter or biology to the same extent.