Q. Which of the following are nitrogen-fixing plants?

1. Alfalfa
2. Amaranth
3. Chickpea
4. Clover
5. Purslane (Kulfa)
6. Spinach

Select the correct answer using the code given below: (UPSC Prelims 2022)
Answer: 1, 3 and 4 only
Notes: The correct answer is [A] 1, 3 and 4 only. This question tests your knowledge of the Leguminosae (Fabaceae) family, which contains plants that form symbiotic relationships with Rhizobium bacteria to fix atmospheric nitrogen.

• Alfalfa (Statement 1 – Correct): Also known as Lucerne, Alfalfa is a highly nutritious perennial legume used as forage. It is well-known for its deep root system and excellent nitrogen-fixing capabilities.
• Chickpea (Statement 3 – Correct): Locally known as Chana, it is a pulse and a key member of the legume family. It helps in restoring soil fertility by fixing nitrogen in its root nodules.
• Clover (Statement 4 – Correct): Species like Trifolium (Red or White Clover) are quintessential nitrogen fixers often used as "green manure" or cover crops to enrich agricultural soil naturally.
• Amaranth (Statement 2 – Incorrect): Amaranth is a pseudocereal belonging to the Amaranthaceae family. While it is nutrient-dense, it does not fix nitrogen.
• Purslane (Statement 5 – Incorrect): Commonly known as Kulfa in India, this is a succulent belonging to the Portulacaceae family. It is a weed/vegetable but lacks nitrogen-fixing symbiosis.
• Spinach (Statement 6 – Incorrect): Spinach belongs to the Amaranthaceae family (formerly Chenopodiaceae). It is a nitrogen-demanding crop rather than a nitrogen-fixing one.

Other common nitrogen-fixing plants frequently mentioned in UPSC include Groundnut, Soyabean, Peas, Beans, and Lentils.