Base saturation refers to the proportion of exchange sites occupied by which type of cations?

Base saturation refers to the proportion of exchange sites occupied by which type of cations?

• A. Anions
• B. Acidic cations (H+ and Al3+)
• C. Basic cations (Ca2+, Mg2+, K+)
• D. Neutral cations (Na+, NH4+)

Answer: (C)

Base saturation is the percentage of a soil’s cation exchange capacity that is occupied by base-forming cations. The key base cations are calcium, magnesium, and potassium (Ca2+, Mg2+, K+), which help neutralize acidity and support plant nutrition. Acidic cations such as hydrogen and aluminum (H+ and Al3+) occupy exchange sites in more acidic soils, lowering base saturation. So the proportion of exchange sites held by Ca2+, Mg2+, and K+ represents the base saturation. For example, if the soil’s CEC is 20 meq/100 g and Ca, Mg, and K together occupy 12 meq, the base saturation is 12/20 = 60%. (Sodium can be considered a base cation in some contexts, but it’s not part of the trio in this framing.)