Microbes as Biofertilizers: Rhizobium, Nostoc and Azotobacter

Microbes as biofertilizers increase the nutrient availability to crop plants either directly or through soil enrichment. These are scientifically made and distributed to farmers. The use of biofertilizers is advantageous mainly because it is environmentally friendly and sustainable. Nowadays, the use of biofertilizers is encouraged over chemical fertilizers, since these don’t disturb the ecological balance.

Key Takeaways: Biofertilizer, Microbes, Azotobacter, Anabaena, Nostoc, Crop plants, Fertilizer, Soil, Microorganisms, Bacteria

---

Biofertilizers

[Click Here for Sample Questions]

Biofertilizers are microorganisms which enrich the soil with nutrients, maximize the ecological benefits and minimize environmental impact.

The microorganisms are cultivated in scientific laboratories in suitable culture media. The cultured microorganism is autoclaved to destroy contamination and then cooled. After cooling, the microorganisms are filled in packets. These packets are distributed to farmers.

---

Types of Biofertilizers

[Click Here for Sample Questions]

Biofertilizers are broadly of three types:

1. Bacteria
2. Cyanobacteria
3. Mycorrhizal fungi

Each of the three types can be further divided:

1. Bacteria

1. Free living nitrogen fixing bacteria: Example- Azotobacter, Rhodopseudomonas
2. Loose association of nitrogen fixing bacteria: Example- Azospirillum
3. Symbiotic nitrogen fixing bacteria: Example- Rhizobium

2. Cyanobacteria

1. Free living nitrogen fixing cyanobacteria: Example- Nostoc
2. Symbiotic nitrogen fixing cyanobacteria: Example- Anabaena

3. Mycorrhizal Fungi

1. Ectomycorrhizae: Ectotrophic mycorrhizae
2. Endomycorrhizae: Endotrophic mycorrhizae

---

Microbes

[Click Here for Sample Questions]

Microbes or microorganisms are tiny living things that are too small to be seen by the naked eye and are found all around us. They can be found in water, soil, and air. They may exist as single-celled forms or as colonies of cells. The most common types of microbes are bacteria, viruses, protozoa, fungi.

Also Read: Evolution

---

Microbes as Biofertilizers

[Click Here for Sample Questions]

Microorganisms used as biofertilizers:

1. Azotobacter:

Azotobacter grows freely in the soil and enriches the soil with nitrogen. They are mostly saprophytic. Azotobacter helps reduce the use of man-made nitrogen fertilizers in paddy fields.

2. Azospirillum:

Azospirillum grows in the rhizosphere of crop plants. They fix atmospheric nitrogen and transfer it to crop plants. This association is called associative mutualism.

3. Rhizobium

Rhizobium forms symbiotic association with roots of higher plants. This can’t fix nitrogen as free organisms, but can only do that while in nodule due to the presence of pink pigments called leghaemoglobin. Leghaemoglobin removes oxygen which helps in nitrogen fixation. Ideally, crops should be grown in nitrogen free soil, otherwise, the ability of Rhizobium to fix nitrogen is hampered.

4. Nostoc

These cyanobacteria or blue green algae grow freely in the soil. They are photosynthetic by nature and can enrich the soil with nitrogen.

5. Anabaena

This nitrogen fixing cyanobacteria can develop a symbiotic association with liverworts, ferns and cycad roots. Anabaena provides nitrogen to the rhizosphere of paddy plants.

6. Ectomycorrhizae

These fungi grow on the surface of the root and in the outer cortex of plants line Pinus. They help in absorption of water, minerals from the soil, production of antimicrobial substances in the rhizosphere.

7. Endomycorrhizae

These fungi grow within the intercellular space of cortical regions of grasses, orchids. They produce a swollen area called a vesicle or finely branched masses called arbuscles. These fungi are also called vesicular arbuscular mycorrhizae. They help in absorption of mineral nutrition, release of growth promoting substances.

---

Advantages of Microbes as Biofertilizers

[Click Here for Sample Questions]

1. They increase the nitrogen and phosphorus available to crops more naturally than chemical fertilizers.
2. They are simple to use, even for novice farmers.
3. They do not pollute the soil or the environment, whereas chemical fertilizers often result in excessive input of nitrogen.
4. They are a cheap, easy-to-use alternative to manufactured chemical fertilizers.
5. They maintain normal soil fertility and make it biologically alive.
6. They increase yield because of the nitrogen and phosphorus they add to the soil.

Also Read:

---

Disadvantages of Microbes as Biofertilizers

[Click Here for Sample Questions]

1. Since biofertilizers are alive microorganisms, they require special care for long-term storage. 
2. If other microorganisms contaminate a particular biofertilizer or if the manufacturer uses the wrong strain, they become ineffective.
3. The soil in itself should contain adequate nutrients for the microorganisms to thrive and work.
4. Biofertilizers cannot totally replace conventional fertilizers.
5. They lose their effectiveness if the soil is not moist.
6. They are less effective if the soil is excessively acidic or alkaline
7. The availability of some biofertilizers depends upon the availability of particular strains of microorganisms or culture media.

---

Things to Remember

• Biofertilizers are living organisms, not chemicals.
• Biofertilizers provide nitrogen and a few other nutrients. They don’t provide a whole spectrum of nutrition to crops.
• Biofertilizers are essentially not connected with maintenance of air, water and texture of soil. They may affect them, but that’s not their primary purpose.
• Our dependence on chemical fertilizers and pesticides sustained and encouraged the growth of chemical input industries which not only affected human health but also disturb the ecological balance.
• Biofertilizers would play a key role in the productivity and sustainability of soil and protect the environment as eco-friendly and cost-effective inputs for the farmers.