What does cation saturation refer to in soil science?

• A. The total amount of cations dissolved in soil water.
• B. The percentage of cation exchange sites occupied by specific cations in the soil.
• C. The ratio of soil acidity to base saturation.
• D. The number of plant nutrients in the soil.

Answer: (B)

Cation saturation is about how the soil’s exchange sites are occupied by different cations. So the soil has a total capacity to hold exchangeable cations (CEC), and cation saturation describes the percentage of those sites taken up by specific cations such as calcium, magnesium, potassium, sodium, and aluminum. This distribution matters for both nutrient availability and soil structure: calcium and magnesium saturation generally supports good soil flocculation and root growth, while excessive sodium saturation can cause soil dispersion and poor water movement, and aluminum saturation points to acidity and potential root toxicity in acidic soils. The other options describe either dissolved ions in soil water, a different ratio not defining saturation, or a vague count of nutrients, none of which capture how the exchange sites are partitioned among the cations.