Home › PYQs › Environment › All questions › 1979 · Nitrogen fixation
UPSC Prelims 1979 · Environment · Nature’s Machinery
Which of the following crops helps in nitrogen fixation?
- (a) Rice
- (b) Wheat
- (c) Maize
- (d) Beans
Show the answer and explanation
Answer: (d) Beans
Beans are legumes: Rhizobium in their root nodules fixes nitrogen.
The idea
Rice, wheat and maize are cereals, members of the grass family. They have no nodule bacteria and must take all their nitrogen from the soil, which is why cereal farming needs so much urea. Beans are legumes and make their own supply through bacteria.
Lightning: a little nitrogen fixed in the air → Bacteria: most natural fixation → Factories (Haber–Bosch process): nitrogen for urea
The trap
UPSC asked this idea three times (1979, 1988, 1992).
Also know
The Haber–Bosch process makes ammonia from nitrogen and hydrogen under high pressure. It now fixes about as much nitrogen as all natural processes on land together, and it is the base of the fertiliser industry.
🔒 Legumes fix nitrogen. Cereals (rice, wheat, maize) do not.