Which soil condition leads to limited oxygen availability?

• A. Saturated soils
• B. Dry soils
• C. Crusted surfaces
• D. Frozen soils

Answer: (A)

When soil pores are filled with water, there’s little or no air space for oxygen to occupy. Oxygen moves much more slowly through water than through air, so diffusion of O2 from the atmosphere into the soil is greatly reduced. As microbes and plant roots consume the available oxygen, the soil can become hypoxic or even anoxic. This is the direct reason why saturated soils limit oxygen availability. Dry soils, crusted surfaces, and frozen soils still allow some air or gas exchange (though they have their own limiting factors), but saturation most directly and consistently creates the low-oxygen conditions.