The correct option is Fragmentation.
Explanation
Decomposition is the process by which complex organic matter is broken down into simpler inorganic substances like carbon dioxide, water, and nutrients. It is an essential part of nutrient cycling and involves five main steps: fragmentation, leaching, catabolism, humification, and mineralisation.
Analysis of the Process:
- Fragmentation: This step involves the physical breakdown of detritus (dead plant and animal remains) into smaller particles. It is primarily carried out by detritivores (e.g., earthworms). This process increases the surface area of the detritus, facilitating subsequent microbial action.
- Leaching: By this process, water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts. It relates to the movement of nutrients rather than physical breakdown.
- Mineralisation: This occurs when humus is further degraded by microbes, resulting in the release of inorganic nutrients. It is a chemical and biological process, not a physical one.
- Nitrification: This is a specific phase in the nitrogen cycle where ammonia is oxidized to nitrite and then to nitrate by bacteria. It is not the general physical breakdown step of decomposition.
Key Takeaway: Fragmentation is the specific phase of decomposition where detritivores physically break down large organic debris into smaller particles to enhance microbial activity.