Consider the following organisms: 1. Agaricus 2. Nostoc 3. Spirogyra Which of the above is/are used as biofertilizer / biofertilizers?

Biofertilizers are preparations containing living microorganisms that enhance nutrient availability to plants [4]. Nostoc is a genus of cyanobacteria (blue-green algae) capable of atmospheric nitrogen fixation, making it a widely used biofertilizer, particularly in paddy fields [3]. While cyanobacteria like Anabaena and Nostoc are primary examples of biofertilizers, other organisms listed do not serve this function [3]. Agaricus is a genus of mushrooms (macro-fungi) primarily cultivated for food rather than nutrient fixation in soil. Spirogyra is a filamentous green alga; although it is a photosynthetic eukaryote, it lacks the specialized nitrogen-fixing capabilities (heterocysts) found in cyanobacteria like Nostoc and is not typically classified or used as a biofertilizer in agricultural practices [1]. Therefore, only Nostoc (2) qualifies as a biofertilizer.

Sources

1. [4] https://www.sciencedirect.com/science/article/abs/pii/S0301479718307916
2. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Geographical advantage > p. 466
3. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Bio-fertilizers > p. 364