By which step of decomposition do water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Leaching
Decomposition breaks dead organic matter (detritus) down into simple inorganic substances. It has five steps: fragmentation, leaching, catabolism, humification and mineralisation. In leaching, water dissolves the soluble inorganic nutrients and carries them down into the soil. There they settle as salts that plants cannot use.
Option (1) Fragmentation — Incorrect. In fragmentation, detritivores such as earthworms break detritus into smaller particles. Nothing is washed down into the soil.
Option (2) Leaching — Correct. In leaching, water-soluble inorganic nutrients go down into the soil and form unavailable salts.
Option (3) Humification — Incorrect. Humification makes humus, a dark, amorphous substance that resists microbes. It does not move nutrients down into the soil.
Option (4) Mineralisation — Incorrect. Mineralisation is the release of inorganic nutrients when humus is broken down further by microbes. It makes nutrients available rather than locking them away.
NCERT Extract:
Decomposition – “… The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralisation. Detritivores (e.g., earthworm) break down detritus into smaller particles. This process is called fragmentation. By the process of leaching, water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.”