Manure
Explanation
Soil amendments are materials added to soil to improve its physical properties, fertility, and capacity to support plant growth. They are broadly classified into organic amendments (derived from biological sources through decomposition) and inorganic/chemical fertilizers (synthetically manufactured or mined minerals).
Analysis of Options
- Urea: Incorrect. Although urea is chemically an organic compound (containing carbon), agricultural urea is synthetically manufactured from ammonia and carbon dioxide. It is not derived from the natural decomposition of biological waste.
- Superphosphate: Incorrect. This is a synthetic inorganic fertilizer produced by treating phosphate rock with sulfuric acid. It is used primarily to supply phosphorus to plants.
- Manure: Correct. Manure is a natural organic substance obtained through the decomposition of plant residues, animal excreta (such as cattle dung), and other biological wastes. It enriches the soil with nutrients and humus, thereby improving soil structure and fertility.
- Potash: Incorrect. Potash refers to various mined and manufactured salts containing water-soluble potassium. It is an inorganic mineral fertilizer.
Key Takeaway:
Manure is an organic soil amendment formed by the natural decomposition of plant and animal waste, whereas fertilizers like urea, superphosphate, and potash are industrially synthesized or mined inorganic compounds.