The aquatic plant commonly used as bio fertilizer in the water-logged rice field is -

Question

UnlockIAS · Accepted Answer

Correct — C, Azolla. Azolla is a small floating water fern that harbours the nitrogen-fixing cyanobacterium Anabaena azollae in cavities of its leaves. Grown on the standing water of submerged (water-logged) paddy fields, this symbiosis fixes atmospheric nitrogen and, when the fern decomposes, releases it into the soil — which is why Azolla is a classic bio-fertilizer for rice. It also multiplies quickly and adds organic matter.

Why the other options are wrong — (a) Wolffia is the world's smallest flowering plant (a rootless duckweed); it is used locally as fodder/food but does not fix nitrogen and is not a paddy bio-fertilizer.  (b) Trapa is the water chestnut (singhara), grown for its edible fruit — a food crop, not a nitrogen-fixing bio-fertilizer.  (d) Lemna (common duckweed) is useful for wastewater treatment and as fodder, but it does not fix atmospheric nitrogen and is not the rice bio-fertilizer meant here.

Concept: Bio-fertilizers are living organisms that enrich soil nutrients. In paddy, the Azolla-Anabaena symbiosis is the key nitrogen-fixing bio-fertilizer: the fern floats on the field's standing water while its cyanobacterial partner converts atmospheric N2 into plant-available nitrogen.

State PCS 2023 Q77 — Science & Technology PYQ with Answer

State PCS 2023 Q77 — Science & Technology PYQ with Answer