Question

An organism used as a biofertilizer for raising soybean crops is?

• A. Nostoc
• B. Azotobacter
• C. Azospirillum
• D. Rhizobium

Answer 1

The correct option is D

Rhizobium

The correct option is D

Explanation of correct option

1. The soybean crop requires nitrogen in high amounts. Around 5 pounds of nitrogen per bushel is required.
2. The addition of biofertilizers helps in enhancing the nutritional content of the soil. These biofertilizers consist of fungi or bacteria that aid in the colonization of rhizospheres, root interior, or rhizoplane of the plants.
3. Rhizobium, a Gram-negative bacteria, has a symbiotic relationship with leguminous plants like alfalfa and soybeans.
4. They convert atmospheric nitrogen into usable forms of nitrates and nitrites.

Explanation of incorrect option

Option A

1. Nostoc refers to Gram-negative cyanobacterium found in both aquatic and terrestrial environments. They fix atmospheric nitrogen and carbon dioxide.
2. Addition of this biofertilizer increases the height and number of leaves of the plant.

Option B

1. Azotobacter refers to Gram-negative, aerobic, free-living, soil bacteria that have thick-walled cysts.
2. It helps in the germination of seeds, increases plant hormone secretion, and fixes nitrogen from the atmosphere.

Option C

1. Azospirillum is a Gram-negative, non-fermentative, microaerophilic, nitrogen-fixing bacteria.
2. It helps in increasing phytohormone synthesis and increases tolerance towards biotic and abiotic stresses. This aids in plant growth.

Final answer

An organism used as a biofertilizer for raising soybean crops is Rhizobium.