Which of the following are nitrogen-fixing plants?

Answer: (a) 1, 3 and 4 only

Alfalfa, chickpea and clover are all legumes with Rhizobium nodules.

Statement by statement

1. ✓ YES — a legume Pea family (Fabaceae), grown as fodder. Its root nodules carry Rhizobium.

2. ✗ NO A leafy green and grain (rajgira/chaulai). Nutritious, but it has no nodules.

3. ✓ YES — a legume Gram (chana) is a pulse, and all pulses are legumes. That is why gram is rotated with wheat.

4. ✓ YES — a legume A classic fodder legume, often sown to enrich pasture soil.

5. ✗ NO A succulent leafy weed and vegetable (Portulaca). No nitrogen-fixing nodules.

6. ✗ NO A leafy vegetable. Rich in iron, but it can’t fix nitrogen.

The idea

Legumes (the pea family) carry Rhizobium bacteria in their root nodules. The bacteria turn N₂ from the air into ammonia, and the plant pays them in sugar.

N₂ in air → Rhizobium in root nodule → Ammonia → plant protein

Why the others are wrong

(b) Adds purslane and spinach, which are leafy greens and not legumes.

(c) Picks three of the non-fixers and drops two legumes.

(d) Includes amaranth, purslane and spinach, none of which fix nitrogen.

The trap

Spinach and amaranth are “healthy greens”, rich in iron and protein, so they feel like nitrogen-fixers. Nutritious is not the same as nitrogen-fixing. Look for the pea family.

Also know

This is why farmers rotate legumes (gram, moong, arhar) with wheat and rice, and plough green manure (dhaincha, sunn hemp) back into the soil. Some non-legumes fix nitrogen too: Azolla (with Anabaena), free-living cyanobacteria, and alder trees (with Frankia).