Certified Crop Advisor Practice Exam

Which of the following plant nutrients is a cation in soils?

1. Calcium

2. Potassium

3. Nitrate

4. Ammonium

The correct answer is: Potassium

Potassium is correctly identified as a cation in soils. Cations are positively charged ions, and potassium falls into this category as it possesses a positive charge in its ion form (K⁺). In soil chemistry, cations are crucial for various plant functions, including nutrient uptake and cellular processes. Calcium and ammonium are also cations; calcium as Ca²⁺ and ammonium as NH₄⁺. However, nitrate is an anion, existing as NO₃⁻, which means it carries a negative charge. Understanding the behavior of these different ions in the soil and their roles in plant nutrition is essential. Cations generally adhere to soil particles, contributing to soil fertility by being readily available for absorption by plant roots.