​Volatilization of ammonia in soil increases with the increase in_______ [AF0 2013].

Correct option is D

​

(D) CaCO₃ content of the soil

Explanation

Ammonia volatilization increases in alkaline soils. Calcareous soils (rich in CaCO₃) favor ammonia loss due to:

Increase in Soil pH

CaCO₃ buffers soil toward alkaline reaction (pH > 7.5).
At higher pH, the equilibrium shifts:

Why (C) Na₂CO₃ is NOT the Correct Exam Answer

Sodium carbonate strongly raises pH, but

It is not commonly present in normal agricultural soils except sodic soils.

The question is general (not specific to sodic soils).

Standard agronomy textbooks associate high CaCO₃ (calcareous soils) with higher ammonia volatilization.