Certified Crop Advisor Practice Exam

What is the primary form of plant-available potassium?

1. K2O

2. KCl

3. KH2PO4

4. KOH

The correct answer is: KCl

The primary form of plant-available potassium is potassium chloride (KCl). This compound is commonly used as a fertilizer due to its high potassium content and solubility in water, making potassium readily available for plant uptake in the soil. Potassium is an essential macronutrient that plays a crucial role in various physiological processes in plants, including osmoregulation, enzyme activation, and photosynthesis. When applied to crops in the form of KCl, it dissociates into potassium ions (K+) and chloride ions (Cl-), with K+ being the form that plants absorb. While K2O (potassium oxide) is often used in literature and on fertilizer labels to express potassium content, it is not directly plant-available. Instead, it serves as a measurement convention, representing the percentage of potassium derived from this oxide. Other forms like KH2PO4 (potassium dihydrogen phosphate) and KOH (potassium hydroxide) are also sources of potassium but are less commonly used primarily for providing potassium in straightforward fertilization practices.