Base saturation indicates what aspect of soil fertility?

• A. The proportion of all exchange sites occupied by exchangeable bases.
• B. The total organic matter content.
• C. The soil's water holding capacity.
• D. The concentration of micronutrients.

Answer: (A)

Base saturation describes what fraction of the soil’s cation exchange capacity is occupied by basic (base) cations—calcium, magnesium, potassium, and sodium. It is usually expressed as a percent of the CEC. This matters for soil fertility because these bases are essential plant nutrients and help maintain soil structure and pH buffering, making nutrients more readily exchangeable to plant roots. When base saturation is high, soils tend to be more fertile and less acidic; when it is low, hydrogen and aluminum ions dominate the exchange sites, signaling acidic conditions that can limit nutrient availability and increase aluminum toxicity. Amending with lime or other amendments can raise base saturation by displacing acidic cations with calcium and magnesium, improving fertility. The other options describe different soil properties (organic matter content, water holding capacity, and micronutrient concentration) that base saturation does not measure directly.