Biofertilizers

Bio-fertilizers are living or biologically active products or microbial inoculants of bacteria, algae and fungi which are able to enrich the soil with nirogen (N), phosphorus (P) and organic matter etc.

Following are some of the important types of bio-fertilizers which can be considered for agro based industries.

• Rhizobium Biofertilizer:- 
• Rhizobium is a symbiotic bacteria forming root nodules in legume plants. 
• The nodules act as miniature nitrogen production factories in the fields. The nodule bacteria fix more nitrogen than  needed for the legume plant and the bacteria.
• The surplus fixed nitrogen is secreted into the field and fertilizes the soil.
• Rhizobium is more efficient than free living nitrogen fixing bacteria and can fix upto 200kg N/ha/year.

• Azotobactor Biofertilizer:-
• Azotobacter are aerobic free living nitrogen fixers. They grow in the rhizosphere (around the roots) and fix the atmospheric nitrogen non-symbiotically and make it available to particular cereals.
• These bacteria produce growth promoting hormones which helps in enhancing growth and yield of the plant.
• These are free living bacteria which grow well on a nitrogen free medium. 
• These bacteria utilize atmospheric nitrogen gas for their cell protein synthesis. This cell protein is then mineralised in soil after the death of Azotobacter cells thereby contributing towards the nitrogen availability of the crop plants.
• Azotobacter spp.,are sensitive to acidic pH, high salts, and temperature above 350C.
• There are four important species of Azotobacter viz. A.Chroococcum, A.agilis, A.paspali and A.vinelandii of which A.chroococcum is most commonly found in our soils.
• The species of Azotobacter are known to fix on an average 10 mg.of N/g of sugar in pure culture on a nitrogen free medium

• Azospirillium Biofertilizer:-
• The are aerobic free living nitrogen fixers which live in associative symbiosis.
• In this type of symbiosis bacteria live on the roots of the host plant and do not form any nodule with the roots.
• It increases crop yield and inoculation benefits crops.
• They also help the host plant by supplying growth hormones and vitamins.
• These bacteria are commonly used for preparation of commercial inoculants.
• Note:-
• Microbial inoculants also known as soil inoculants are agricultural amendments that use beneficial endophytes (microbes) to promote plant health. 
• Many of the microbes involved form symbiotic relationships with the target crops where both parties benefit (mutualism).
• While microbial inoculants are applied to improve plant nutrition, they can also be used to promote plant growth by stimulating plant hormone production
• Blue Green Algae:-
• Blue Green Algae (BGA or cyanobacteria) like Nostoc or Anabaena are free living photosynthetic organisms also capable of fixing the atmospheric nitrogen.
• In the flooded rice fields blue green algae serves as the nitrogen biofertilizer.
• When environmental conditions are just right, blue-green algae can grow very quickly in number. 
• Most species are buoyant and will float to the surface, where they form scum layers or floating mats. When this happens, we call this a "blue-green algae bloom."
• Azolla Biofertilizer:-
• Azolla is a water fern inside which grows the nitrogen fixing blue green algae Anabaena.
• It contains 2-3% nitrogen when wet and also produces organic matter in the soil.
• The Azolla Anabaena combination type biofertilizer is used in the whole world. 
• The only constraint in azolla is that it is an aquatic plant and water becomes a limiting factor in growing it particularly in the summer months.
• Phosphorus Solubilising Biofertilizer:-
• Phosphorus is an important element required for plant growth. 
• This element is needed for nodulation by rhizobium.
• Some micro-organisms are capable of of solubilising immobilised phosphorus  making it available to plants for absorption.
• Mycorrhizal Fungi Biofertilizer:-
• It acts as a biofertizer and occurs naturally on roots of the forest trees and crop plants.
• The fungi has the ability to dissolve and absorb phosphorus that plant roots can not readily absorb.
• In soils low in nutrients, there is an increased absorption of nutrients by plants infected with Mycorhhiza.