Formation affected by organisms
Explanation
Humus is a dark, amorphous, and organic material found in soil, resulting from the decomposition of plant and animal residues. It is a vital component that influences soil fertility, structure, and moisture retention.
Option Analysis
- Formation affected by organisms is Correct: The formation of humus is fundamentally a biological process. Soil organisms (the biosphere), including bacteria, fungi, earthworms, and insects, break down dead organic matter. The rate of humus formation is heavily influenced by the population and activity of these organisms, which in turn depend on climatic conditions.
- It is inorganic is Incorrect: Humus is organic, not inorganic. It is derived from carbon-based life forms (plants and animals). The inorganic portion of soil consists of minerals derived from the weathering of parent rocks.
- Only parent rock matters is Incorrect: While the parent rock determines the mineral composition and texture of the soil, it does not dictate humus formation. Humus accumulation is primarily determined by the biological activity and climate (which affects decomposition rates), regardless of the underlying rock type.
- Not essential is Incorrect: Humus is highly essential. It improves soil structure by binding particles into aggregates, increases water-holding capacity, and serves as a reservoir of nutrients like nitrogen and sulfur for plant growth.
Key Takeaway: Humus is the organic component of soil formed through the decomposition of biomass by soil microorganisms; its formation is governed by the biological factor of soil formation rather than the parent rock.