Question

What is the critical value of deficiency of zinc in Indian soils?

• A. 2.5--4.5 mg/kg
• B. 1.5--2.5 mg/kg
• C. 0.4--1.2 mg/kg
• D. 4.5--6.5 mg/kg

Hint:

In zinc-deficient soils, foliar sprays or soil application of zinc sulphate (ZnSO$_{4}$) is the best corrective measure.

Answer 1

The Correct Option is C

Step 1: Importance of Zinc.
Zinc is a vital micronutrient for plants, required for enzyme activity, chlorophyll synthesis, and growth regulation.
It plays a role in auxin metabolism and protein synthesis.
Step 2: Deficiency in Indian soils.
Many Indian soils, especially calcareous and alkaline soils, are deficient in zinc.
This deficiency is common in wheat, rice, and maize-growing regions.
Step 3: Critical limit.
The critical value of zinc deficiency is defined as the concentration below which plant growth and yield are adversely affected.
For Indian soils, this threshold lies between 0.4--1.2 mg/kg of available zinc.
Step 4: Analysis of options.
- (A) 2.5--4.5 mg/kg: Too high, plants rarely suffer deficiency at this level.
- (B) 1.5--2.5 mg/kg: Higher than the actual critical deficiency level.
- (C) 0.4--1.2 mg/kg: Correct, this is the accepted range for zinc deficiency in Indian soils.
- (D) 4.5--6.5 mg/kg: Very high, soils at this level are zinc sufficient.
Step 5: Conclusion.
Hence, zinc deficiency in Indian soils is considered critical when available zinc falls between 0.4--1.2 mg/kg.