The correct option is 1 and 3 only.
Explanation
Soil formation (pedogenesis) is a complex exogenic process driven by five major factors: parent material, topography, climate, biological activity, and time. Biological activity involves the interaction of flora and fauna with the soil, contributing to organic matter accumulation, nutrient cycling, and structural modification.
Statement-wise Analysis:
- Statement 1 is Correct: Organisms such as ants, termites, and earthworms act as agents of bioturbation. They actively rework the soil by moving materials vertically, bringing subsoil to the surface and carrying surface organic matter into deeper layers, thereby facilitating mixing and aeration.
- Statement 2 is Incorrect: Earthworms have a profound effect on both the texture and chemistry of the soil. They ingest soil and organic matter, breaking them down and excreting them as casts. This process modifies soil texture by creating granular aggregates and alters soil chemistry by increasing nutrient availability and decomposition rates.
- Statement 3 is Correct: The influence of larger animals (such as burrowing rodents, moles, or grazing herbivores) is predominantly mechanical. Their activities, including digging, burrowing, and trampling, physically loosen the soil, break down aggregates, and assist in physical weathering, although they also contribute organic waste.
Key Takeaway:
Biological activity is essential for soil development; small organisms and invertebrates significantly alter soil chemistry and texture through digestion and mixing, while larger animals primarily contribute to soil formation through mechanical disturbance.