UPSC Prelims 2000 · General Studies

Question 115: Science and Technology

Which one of the following organisms can serve as a biofertilizer for rice crop?

aBlue-green algae

bRhizobium sp

cMycorrhizal fungi

dAzotobacter sp

AnswerThe answer is (a).

Blue-green algae, or cyanobacteria such as Anabaena, Nostoc and Aulosira, fix atmospheric nitrogen in flooded rice fields, and they are used as a biofertilizer for rice, often along with the water fern Azolla. Rhizobium works with legume roots, mycorrhizal fungi help plants take up phosphorus, and Azotobacter is used for non-legumes grown in aerated soils.

Why each option is right or wrong

(a) Right: blue-green algae fix nitrogen in rice paddies.
(b) Rhizobium lives in the root nodules of legumes, not rice.
(c) Mycorrhizal fungi help phosphorus uptake and are not the usual rice biofertilizer.
(d) Azotobacter is used for crops of well-aerated soil, not waterlogged rice.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2000, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.