Potassium (K) is present in soil in different forms. Plants prefer to take up K from the soil as:
(A). Exchangeable K
(B). Solution K
(C). Total or Mineral K
(D). Non-exchangeable K
Choose the correct answer from the options given below:
Show Hint
Although mineral K makes up over \(90-98\%\) of total soil potassium, only \(1-2\%\) is in the readily available (solution + exchangeable) form at any given time.
Step 1: Understanding the Concept:
Soil potassium exists in dynamic equilibrium among four chemical pools with varying levels of plant availability. Step 2: Detailed Explanation:
The four pools of soil potassium, in order of decreasing availability and plant preference, are:
1. Solution K (B): Potassium ions dissolved in soil water. This pool is immediately available for root uptake.
2. Exchangeable K (A): Ions held electrostatically on clay and organic matter surfaces. This pool is in rapid equilibrium with solution K and is highly available.
3. Non-exchangeable K (D): Potassium trapped within the interlayer spaces of 2:1 clay minerals. It is slowly released to exchangeable and solution forms.
4. Total or Mineral K (C): Structural potassium bound within primary minerals (micas and feldspars). This pool is unavailable to plants and is only released over long periods through weathering.
- Thus, the preference and availability sequence is: (B) \(\rightarrow\) (A) \(\rightarrow\) (D) \(\rightarrow\) (C). Step 3: Final Answer:
The correct order of plant availability and preference is (B), (A), (D), (C).
