What commonly happens in soils that are saturated?

• A. Oxygen becomes abundant
• B. Oxygen becomes limited
• C. Nitrogen fixation occurs
• D. Water drains quickly

Answer: (B)

In soils that are saturated, all the pore spaces are filled with water, leaving little air. Oxygen moves into soil and to roots mainly through air-filled pores, so when those pores are waterlogged, diffusion of oxygen slows dramatically and the soil becomes low in oxygen. This creates anaerobic conditions that affect roots and many soil processes. That’s why the typical outcome is that oxygen becomes limited. The other options don’t fit: abundant oxygen can’t be maintained when pores are waterlogged, water isn’t draining quickly under saturation, and nitrogen fixation isn’t a guaranteed result of saturation and depends on specific microbial and plant conditions.