Question

Given below are two statements :
Statement (I) : Soil having high amount of hydrogen ions affect the nutrient availability.
Statement (II) : Increased soil pH beyond 7.0 increases the availability of micronutrients.
In light of the above statements, choose the most appropriate answer from the options given below. :

• A. Both Statement (I) and Statement (II) are correct
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect
• D. Statement (I) is incorrect but Statement (II) is correct

Hint:

- Most plant nutrients are at their maximum availability in the slightly acidic to neutral pH range of 6.0 to 7.0.
- Micronutrients (except Mo) become highly available in acidic soils (pH < 6.0) and can reach toxic levels, while they become deficient in alkaline soils (pH > 7.0).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Soil reaction (pH) is a master variable that governs the chemical forms and solubility of plant nutrients.
A high concentration of hydrogen ions (\(\text{H}^+\)) indicates an acidic soil, which significantly alters nutrient dynamics and microbial activity.

Step 2: Detailed Explanation:
Let us analyze the two statements in detail:
- Statement (I):
Soil with a high concentration of hydrogen ions (\(\text{H}^+\)) is highly acidic (low pH).
This acidity directly affects nutrient availability.
For instance, in strongly acidic soils, phosphorus is precipitated as insoluble iron and aluminum phosphates, while essential basic cations like calcium (\(\text{Ca}^{2+}\)), magnesium (\(\text{Mg}^{2+}\)), and potassium (\(\text{K}^+\)) are leached out of the root zone.
Therefore, Statement (I) is correct.
- Statement (II):
As the soil pH increases beyond 7.0 (alkaline conditions), the availability of most essential micronutrients—including iron (\(\text{Fe}\)), manganese (\(\text{Mn}\)), zinc (\(\text{Zn}\)), copper (\(\text{Cu}\)), and boron (\(\text{B}\))—decreases significantly.
This occurs because these metallic ions react with hydroxyl (\(\text{OH}^-\)) and carbonate (\(\text{CO}_3^{2-}\)) ions to form highly insoluble hydroxides and carbonates.
The only exception is molybdenum (\(\text{Mo}\)), whose availability increases with pH.
Therefore, Statement (II) is incorrect.
Thus, Statement (I) is correct but Statement (II) is incorrect.

Step 3: Final Answer:
The correct option is (C), as Statement I is correct and Statement II is incorrect.