gt; 8.5$), which chemical soil amendment is most widely ... Explore step-by-step solution, answer key, and exam analytics on GATE AG Prep Portal." />
gt; 8.5$), which chemical soil amendment is most widely ... Explore step-by-step solution, answer key, and exam analytics on GATE AG Prep Portal." />
Question Bank • QB_IDE_ADV_081MCQ • 1 Mark
Section 5: Irrigation and Drainage Engineering
Agricultural Drainage
Subtopic: Leaching requirement and salinity control
Question Statement:
For reclaiming alkali (sodic) soils having an Exchangeable Sodium Percentage ($ESP > 15\%$) and high pH (gt; 8.5$), which chemical soil amendment is most widely applied to displace exchangeable sodium from the clay exchange complex?
In sodic soils, dispersed sodium ions ($2\text{Na}^+$) adsorbed on clay surfaces must be replaced by bivalent calcium ions ($\text{Ca}^{2+}$) via cation exchange:
$\text{Clay-Na}_2 + \text{CaSO}_4 \rightleftharpoons \text{Clay-Ca} + \text{Na}_2\text{SO}_4$
The displaced soluble sodium sulfate is subsequently leached out below the root zone by irrigation water. Agricultural gypsum is the primary economical calcium-supplying amendment. Option A is correct.