Which soil test component helps guide lime or fertilizer decisions by indicating the proportion of CEC occupied by basic cations?

• A. Base saturation percentages
• B. Electrical conductivity
• C. Organic matter content
• D. Sodium adsorption ratio

Answer: (A)

Base saturation percentages show how much of the soil’s cation exchange capacity is occupied by basic cations such as calcium, magnesium, potassium, and sodium. This matters for lime or fertilizer decisions because it directly reflects how many exchange sites are filled with non-acidic cations versus acidic ones like hydrogen and aluminum. If base saturation is low, many sites are held by acidity, and applying lime (which supplies Ca and Mg and raises pH) helps replace H and Al on the exchange complex, improving nutrient availability. Fertilizers that supply Ca, Mg, and K can also raise base saturation toward more favorable levels. When base saturation is already high in basic cations, lime may be unnecessary, or the focus shifts to balancing specific nutrients without overcorrecting pH.

Electrical conductivity measures soil salinity, not how much of the exchange complex is occupied by basic cations. Organic matter content influences nutrient holding capacity but doesn’t directly indicate the proportion of CEC filled by basic cations. Sodium adsorption ratio relates to sodium’s effect relative to calcium and magnesium, not the overall base saturation of the exchange complex.