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 distinct steps: fragmentation, leaching, catabolism, humification, and mineralization.Detailed Analysis:
- Leaching Leaching: This is the specific process within decomposition where water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts. It removes nutrients from the topsoil, making them inaccessible to plant roots in the immediate term.
- Percolation Percolation: This refers to the physical movement and filtering of fluids (usually water) through porous materials like soil. While leaching occurs due to percolation, the specific phenomenon of nutrient transport and precipitation described in the question is defined as leaching.
- Infiltration Infiltration: This is the process by which water on the ground surface enters the soil. It is the initial entry of water, distinct from the subsequent downward movement of nutrients.
- Calcification Calcification: This is a soil formation process involving the accumulation of calcium salts (carbonates) in soil layers, typically occurring in arid or semi-arid regions. It is not the general term for the downward movement of water-soluble nutrients.
Key Takeaway:
Leaching is the step in decomposition responsible for the downward movement of water-soluble nutrients into lower soil horizons, often precipitating them as unavailable salts.