Certified Crop Advisor Practice Exam

What component neutralizes soil acidity when lime is applied?

1. H2O

2. CO3-

3. PO4^3-

4. SO4^2-

The correct answer is: CO3-

When lime is applied to soil, calcium carbonate (CaCO3), the primary component of lime, acts to neutralize soil acidity. The part of this compound that is particularly responsible for the neutralization process is the carbonate ion (CO3^2-). This ion reacts with hydrogen ions (H+) in the soil, which contributes to acidity. By combining with the hydrogen ions, CO3^2- reduces the concentration of these acidic ions, thereby increasing the pH level of the soil and making it less acidic. In this context, the other options do not have a direct role in neutralizing soil acidity. Water (H2O) does not participate in the neutralization process specifically. Phosphate ions (PO4^3-) are more associated with plant nutrition rather than directly affecting soil acidity. Sulfate ions (SO4^2-) similarly do not have a neutralizing effect on acidity in the way that carbonate ions do. Therefore, the presence of CO3^2- is fundamental in the liming process to correct soil pH and improve soil health for agricultural purposes.