Question

Which one of the following is useful in rice fields?
A) Rhizobium
B) Clostridium
C) Anabena
D) Ferrobacterium

Answer 1

Organisms that can fix atmospheric nitrogen to make available to the rice plant is very beneficial for their growth (As rice consume a large amount of nitrogen). These organisms can present in both free-living forms or in symbiotic form.

Complete step by step answer: Nitrogen-fixing blue-green algae has special kind of cells present in them called heterocyst which helps in nitrogen fixation. Rhizobium, Anabaena, Azospirillum and Azotobacter are considered as biofertilizer as they enhance the nutrients content of the soil which is uptaken by the plant. Rhizobium fixes nitrogen only when it is present symbiotically with the root of a leguminous plant (Example: pulses, soyabean, etc.). It is not present in rice as rice belongs to the Gramineae family. Azospirillum and Azotobacter also enhance the nitrogen content of the soil but they are free-living in the soil, that means they do not live in symbiotic relation with any organism or plant.
Anabaena (A blue-green algae) lives symbiotically with Azolla (water fern) and fix nitrogen and enhance the nitrogen content of the soil by ninety per cent. These are used in the paddy or rice field.
Ferrobacterium provides iron to the field but rice is the heavy feeder of nitrogen.
Hence, the correct answer is option C.

Note: Nowadays many people have shifted to organic food as they have become more conscious towards their health, so, the farmers have also started practising organic farming. In this type of farming, many types of chemicals are not used for fulfilling nutritional requirements; they are using biofertilizers which consist of main bacteria, fungi and Cyanobacteria.