It facilitates nutrient cycling by releasing minerals from organic matter
Explanation
Humus is the dark, amorphous, and colloidal organic substance that forms in soil when plant and animal matter decays. It represents the stable fraction of soil organic matter and plays a critical role in the fertility and physical structure of forest soils.
Option Analysis
- It increases soil compaction and density is Incorrect: Humus improves soil structure by binding soil particles into aggregates. This creates pore spaces, thereby increasing porosity and aeration. Consequently, humus decreases soil bulk density and prevents compaction, rather than increasing it.
- It inhibits the proliferation of soil microbes is Incorrect: Humus serves as a primary source of carbon and energy for soil microorganisms. Its presence supports a vast population of bacteria and fungi. Therefore, it promotes, rather than inhibits, the proliferation of soil microbes.
- It facilitates nutrient cycling by releasing minerals from organic matter is Correct: The most significant ecological function of humus is its role as a nutrient reservoir. It holds nutrients such as nitrogen, phosphorus, and sulfur in organic forms. Through the process of mineralization, microbes slowly break down humus, releasing these inorganic minerals back into the soil solution for plant uptake, thus facilitating the nutrient cycle.
- It absorbs atmospheric oxygen for root respiration is Incorrect: While humus improves soil aeration by enhancing structure, it does not chemically absorb atmospheric oxygen for roots. Roots obtain oxygen from the air trapped within the soil pore spaces created by soil aggregates.
Key Takeaway
Humus is essential for soil fertility as it improves soil structure (porosity), retains moisture, and acts as a slow-release reservoir of nutrients through the process of mineralization.