Soil compaction reduces which properties?

• A. Bulk density
• B. Carbon content
• C. Soil temperature
• D. Oxygen, infiltration, and root growth

Answer: (D)

Soil compaction changes the soil’s pore structure, which controls gas exchange, water movement, and root penetration. When the soil is compacted, pore space—especially the large, connected pores that air and water use—gets crushed. That reduces air-filled porosity, so oxygen diffusion to roots and soil microbes drops. Water movement also slows, so infiltration capacity falls and rainfall tends to run off rather than soak in. The compacted, dense layer presents a physical barrier to root growth, making it harder for roots to extend and access water and nutrients. Because these are the key effects of compaction, oxygen availability, infiltration, and root growth are reduced. (Bulk density actually increases with compaction, not decreases; carbon content and soil temperature aren’t the primary, direct reductions caused by compaction.)