Step 1: Importance of Zinc.
Zinc is an essential micronutrient for plants, crucial for enzyme function, chlorophyll production, and growth regulation.
It is involved in auxin metabolism and protein synthesis.
Step 2: Deficiency in Indian soils.
Many Indian soils, particularly calcareous and alkaline types, exhibit zinc deficiency.
This deficiency is prevalent in regions where wheat, rice, and maize are cultivated.
Step 3: Critical limit.
The critical zinc deficiency level is defined as the concentration below which plant growth and yield are negatively impacted.
For Indian soils, this threshold ranges from 0.4 to 1.2 mg/kg of available zinc.
Step 4: Analysis of options.
- (A) 2.5--4.5 mg/kg: Excessively high; plants rarely experience deficiency at this level.
- (B) 1.5--2.5 mg/kg: Exceeds the actual critical deficiency level.
- (C) 0.4--1.2 mg/kg: Accurate; this is the recognized range for zinc deficiency in Indian soils.
- (D) 4.5--6.5 mg/kg: Very high; soils at this concentration are zinc-sufficient.
Step 5: Conclusion.
Consequently, zinc deficiency in Indian soils is deemed critical when available zinc levels are between 0.4 and 1.2 mg/kg.