Question

In highly leached acidic soils, low absorption of micro-nutrients is expected for

• A. Iron and Manganese
• B. Boron and Molybdenum
• C. Calcium and Magnesium
• D. Phosphorous and Potassium

Hint:

At acidic pH ($< 5.5$): Fe, Mn, Zn, Cu, Al availability increases (toxicity risk). Mo and B availability decreases.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Soil pH strongly influences chemical solubility, precipitation, and biological availability of micronutrients in the soil solution.

Step 2: Detailed Explanation:
Micronutrient availability behavior across the pH spectrum:
1. Cationic Micronutrients (Fe, Mn, Zn, Cu): Solubility and availability increase drastically in acidic soils (often reaching toxic levels at pH $< 5.0$).
2. Anionic Micronutrients (Molybdenum and Boron):
- Molybdenum (Mo): Precipitated as insoluble iron/aluminum molybdates at low pH; availability decreases sharply in acidic soils.
- Boron (B): Highly water-soluble non-ionized boric acid is rapidly leached out under high rainfall leaching in acidic profiles.
Hence, low plant uptake in leached acid soils is expected for Boron and Molybdenum.

Step 3: Final Answer:
Thus, low absorption is expected for Boron and Molybdenum, matching option (B).