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UPSC Prelims 1981 · Agriculture · Soils
Gypsum is added to the soil
- (a) To increase the alkalinity
- (b) To decrease the acidity
- (c) To decrease the alkalinity
- (d) As an insecticide
Show the answer and explanation
Answer: (c) To decrease the alkalinity
Gypsum (calcium sulphate) replaces sodium in alkaline (sodic) soils, lowering alkalinity.
Why the others are wrong
(a) Gypsum reduces alkalinity, not increases it.
(b) Acidic soils get lime, not gypsum.
The trap
Lime and gypsum are both calcium — lime fixes acidic soil, gypsum fixes alkaline soil.
🔒 Acidic soil → lime. Alkaline/sodic soil → gypsum.