Biology: Biofertilizers

Biofertilizers are defined as preparations containing living cells or latent cells of efficient strains of microorganisms that help crop plants uptake of nutrients, by their interactions in the rhizosphere when applied through seed or soil. They accelerate certain microbial processes in the soil which augment the extent of availability of nutrients in a form easily assimilated by plants. They can be grouped in different ways based on their nature and function.

Nitrogen-fixing Biofertilizer: Azotobacter, Beijerinckia, Clostridium, Klebsiella, Anabaena, Nostoc, Rhizobium, Frankia, Anabaena azollae.
Phosphorus-solubilizing/mobilizing Biofertilizers: Bacillus megatherium var. phosphaticum, Aspergillus, Pezizella ericae.
Biofertilizers for micronutrients: Bacillus spp.
Plant Growth Promoting Rhizobacteria: Pseudomonas fluorescens.

Cyanobacteria (blue-green algae) and Azolla are used as biofertilizers. However, Alfalfa is a perennial flowering plant of the pea family.

Nitrogen-fixing Biofertilizer: Azotobacter, Beijerinckia, Clostridium, Klebsiella, Anabaena, Nostoc, Rhizobium, Frankia, Anabaena azollae.
Phosphorus-solubilizing/mobilizing Biofertilizers: Bacillus megatherium var. phosphaticum, Aspergillus, Pezizella ericae.
Biofertilizers for micronutrients: Bacillus spp.
Plant Growth Promoting Rhizobacteria: Pseudomonas fluorescens.

Cyanobacteria (blue-green algae) and Azolla are used as biofertilizers. However, Alfalfa is a perennial flowering plant of the pea family.

• Rhizobium:

This bacterium forms a symbiotic relationship with the root nodules of legumes (e.g., beans, peas) and fixes atmospheric nitrogen, making it available to the plant.

• Blue-green algae (cyanobacteria):

These photosynthetic microorganisms, including species like Anabaena and Nostoc, are found in various environments, including rice paddies. They can fix atmospheric nitrogen and are a significant source of nitrogen in rice fields.

• Azolla:

This water fern has a symbiotic relationship with the cyanobacterium Anabaena azollae, which fixes nitrogen within the leaf cavities of the fern. Azolla is often used as a biofertilizer in rice paddies, providing nitrogen to the plants.

Nostoc is a blue-green alga (cyanobacteria) that can fix atmospheric nitrogen into a usable form for plants.

Anabaena is another blue-green algae that also has the ability to fix nitrogen. Some species of Anabaena form symbiotic relationships with plants like Azolla, further enhancing nitrogen fixation.

Azotobacter is a bacterium that can also fix nitrogen, especially in the soil. Unlike Nostoc and Anabaena, Azotobacter is not an algae.

Mycorrhiza refers to the symbiotic relationship between fungi and plant roots, where the fungi help the plant absorb nutrients. While mycorrhizae enhance plant growth and nutrient uptake, they don't directly fix nitrogen from the atmosphere.

The demand for milk and meat in India is creating a new potential, in profitability of animal husbandry as an occupation. Yet, at some time there is a substantial decline in fodder availability. The search for alternatives led to a wonderful plant Azolla which holds the promise of providing a sustainable food for livestock. Azolla, in turn, provides the carbon source and favourable environment for the growth and development of algae. It is this unique symbiotic relationship that makes Azolla a wonderful plant with a high protein content.

Azotobacter is a bacteria. Azotobacter naturally fixes atmospheric nitrogen in the rhizosphere (the zone surrounding the root of plants). So option (d) is not correctly matched. Other three options are correctly matched.

Brown algae (Phaeophyceae) are distinguished by their brown color, thanks to the pigment fucoxanthin. They are also primarily marine organisms. Kelp is a well-known example of brown algae.

Green algae (Chlorophyta) are characterized by their green color due to the presence of chlorophyll. They are found in both freshwater and marine environments. Green algae are evolutionarily closer to land plants than other algae.

Cyanobacteria or blue-green algae is an example of biofertilizer, which helps in fixing atmospheric nitrogen. Blue-green algae are mainly used as biofertilizer in the crop paddy.