Numerous microorganisms are useful for the soil and help in absorbing necessary nutrients in the environment. By picking out the important and efficient microorganisms and culturing them, their benefits can be increased. These microorganisms can be added to the soil directly. These are called biofertilizers. 

Biofertilizers are defined as materials that embody microorganisms that are required by plants and crops to increase plant growth. The fertility of the soil is increased by these microbes. Their major sources are organisms from phylum cyanobacteria, phylum fungi, and bacterial groups. The common types of biofertilizers are bacterial, fungal, algal, and actinomycetes. Biofertilizers differ from fertilisers as they do not contain synthetic chemicals. A few examples are Rhizobium, Azotobacter, and Azoprillium. 

Role of Biofertilizers

Biofertilizers contain living microorganisms. They differ in impact and action based on the combination. They can even be applied alone.

The various roles of biofertilizers are:

• They fix nitrogen from the atmosphere into the soil and root nodules. This makes nitrogen easily available for taking up by the plant. 
• The insoluble forms of chemical compounds, such as phosphate like tricalcium, aluminium phosphate, and iron phosphate, are converted to soluble forms by biofertilizers.
• They help to search for phosphates in the soil layers.
• They nurture the growth of plants by secreting hormones and anti-metabolites.
• They mineralise the soil by decomposing complex organic substances. 
• They improve the yield of the plant by at least 10 to 25%, without causing any harmful effects to the soil.
• They increase the availability of nutrients in the soil for the plant.

Characteristics of Common Biofertilizer Microorganisms

The common microorganisms used as biofertilizers are listed below.

• Rhizobium: It is the most widely used as a biofertilizer. It is also observed to be very effective with plants. Legumes have a symbiotic association with Rhizobium. It fixes nitrogen from the atmosphere. 

The amount of Rhizobium available depends on the number of legumes in the field. If there are fewer legume plants, its function decreases. Not all legumes are compatible with the Rhizobium microorganism. Rhizobium is specific to legumes of the nod factor.

• Azospirillum: The microbe is gram-negative, aerobic, and microaerophilic. It is known as an important diazotroph. Graminaceous plants form associative symbiotic relations with Azospirillum. It is recommended for growing rice.

• Azotobacter: It is a free-living, gram-negative bacteria that are present in the rhizosphere soil of plant species. This is also a well-known diazotroph that helps in fixing nitrogen from the atmosphere. They are widely used for commercial agriculture purposes. They are capable of secreting phytohormones as well.

• Blue-Green Algae: Among all the algae, blue-green algae is the only one capable of fixing biological nitrogen. This is due to the presence of heterocysts. They embody chloroplasts, making them photosynthetic. It improves the fertility of the soil and enriches organic matter. 

Biofertilizers in India 

The following represents the microbes used as biofertilizers in India

Application Methods of Biofertilizers

The following 3 methods are the ways to apply biofertilizers:

• Root dipping the seedling 

This method is used for crops such as rice or paddy. In this method, a bed of water contains the sowed seedlings. It is kept this way for 8 to 10 hours.

• Seed Treatment 

In this method, the nitrogenous and phosphorus fertilisers are mixed in certain proportions. The seeds are soaked in this mixture. They are then left for drying. The dried seeds are then sowed. 

• Soil treatment 

In this method, the compost fertilisers and biofertilizers are mixed and kept overnight. It is scattered in the soil.

Advantages of Biofertilizers

Biofertilizers are unique in their functions compared to chemical fertilisers. The advantages of biofertilizers are listed below.

• Act as a supplement to chemical fertilisers
• Cost-effective and help in lesser use of chemical fertilisers
• Atmospheric nitrogen is directly fixed by the biofertilizer microbes
• Improves growth of plants by increasing the availability of hormones and vitamins
• They improve yield by at least 10–20%
• Improve the soil texture and maintain the fertility of the soil
• It is a sustainable method

Conclusion

There are plenty of microorganisms that can be used to aid agricultural produce. These are called biofertilizers. Biofertilizers are microbes that are embodied in fertilisers to improve plant growth in a sustainable way. The role of biofertilizers is to fix nitrogen, increase plant growth and yield, and mineralise the soil. 

Some common examples of microbes are Rhizobium, Azotobacter, and blue-green algae. A table discussing the common microbes used in India is also given in the article. There are 3 methods by which fertilisers can be applied: seedling root dipping, soil, and seed treatment. They also have many advantages like increased mineralization, increased yield, and cost-effectiveness.