The correct option is Leaching.
Explanation
Decomposition is the process by which decomposers break down complex organic matter into inorganic substances like carbon dioxide, water, and nutrients. This process is largely oxygen-requiring and involves several specific steps: fragmentation, leaching, catabolism, humification, and mineralization.
Analysis of Processes:
- Leaching (Correct): In this process, water-soluble inorganic nutrients dissolve in percolating water and move down into the lower soil horizons. Consequently, they precipitate as unavailable salts, becoming temporarily inaccessible to plants.
- Fragmentation: This involves the physical breakdown of detritus (dead organic matter) into smaller particles by detritivores, such as earthworms. It increases the surface area for microbial action but does not directly involve the downward movement of dissolved nutrients.
- Catabolism: This is the chemical breakdown where bacterial and fungal enzymes degrade detritus into simpler inorganic substances.
- Humification: This process leads to the accumulation of a dark-coloured, amorphous substance called humus, which is highly resistant to microbial action and serves as a reservoir of nutrients.
Key Takeaway:
Leaching is the specific step in decomposition responsible for the vertical transport of water-soluble nutrients into deeper soil layers, often removing them from the immediate reach of plant roots.