Q4. The bio-fertilizer used as a supplementary food for the cattle, especially for milking bovines is:
[RPSC RAS Prelims (2016)]
(A) Azotobacter
(B) Azospirillum
(C) Rhizobium
(D) Azolla
Answer: (D) Azolla
Explanation: Azolla is a small floating aquatic fern used both as a biofertiliser and, after suitable preparation, as protein-rich supplementary animal feed. Its association with nitrogen-fixing cyanobacteria supports paddy cultivation. The other options are nitrogen-fixing bacteria, not comparable aquatic feed plants.
Q3. Directions: The following items consist of two statements, Statement I and Statement II. You are to examine these two statements carefully and select the answers to these items using the code given below:
Statement I: Growth of plants is smooth with a complete fertilizer.
Statement II: A complete fertilizer always contains N, P, K.
[UPSC NDA General Ability Test (19 April 2015)]
(A) Both the statements are individually true and Statement II is the correct explanation of Statement I.
(B) Both the statements are individually true but Statement II is not the correct explanation of Statement I.
(C) Statement I is true but Statement II is false.
(D) Statement I is false but Statement II is true.
Answer: (B) Both the statements are individually true but Statement II is not the correct explanation of Statement I.
Explanation: A complete fertiliser supplies all three primary nutrients: nitrogen, phosphorus and potassium. Both statements were treated as true by the paper’s answer key, but the second was not accepted as a sufficient explanation of the first. Crop growth also depends on other nutrients and conditions.
Q2. Consider the following organisms: 1. Agaricus, 2. Nostoc, 3. Spirogyra. Which of the above is/are used as biofertilizer/biofertilizers?
[UPSC CSE Prelims GS Paper I (2013)]
(A) 1 and 2
(B) 2 only
(C) 2 and 3
(D) 3 only
Answer: (B) 2 only
Explanation: Nostoc is a cyanobacterium capable of fixing atmospheric nitrogen and can enrich soils as a biofertiliser. Agaricus is a mushroom genus, and Spirogyra is a filamentous green alga not normally used as a nitrogen-fixing biofertiliser. Therefore only the second organism qualifies.
Q1. Which of the following is/are used as biofertilizers? 1. Azolla, 2. Blue-green algae, 3. Alfalfa. Choose the correct answer using the codes given below.
[UPPSC PCS Prelims (2002)]
(A) 2 only
(B) 1 and 2
(C) 1 and 3
(D) 1, 2 and 3
Answer: (B) 1 and 2
Explanation: Azolla hosts nitrogen-fixing cyanobacteria, and certain blue-green algae also fix atmospheric nitrogen and enrich cultivated soils. Alfalfa is itself a nitrogen-fixing leguminous crop, generally regarded here as fodder or green manure rather than a microbial biofertiliser. Hence the first two qualify.
