Phosphate-Solubilizing Bacteria: These bacteria help in converting insoluble phosphorus into a soluble form that can be easily absorbed by plants. Examples include Bacillus megaterium and Pseudomonas striata.
Silicate Solubilizing Bacteria: These bacteria help in releasing silicon from insoluble silicates in the soil, making it available to plants. Examples include Bacillus spp. and Pseudomonas spp.
Potassium-Solubilizing Bacteria: These bacteria help in solubilizing potassium from insoluble minerals in the soil, making it available to plants. Examples include Bacillus fastidiosus and Bacillus mucilaginosus.
Zinc-Solubilizing Bacteria: These bacteria help in solubilizing zinc from insoluble sources in the soil, making it easily available to plants. Examples include Bacillus spp. and Pseudomonas spp.
Microbial Inoculants: These are mixed cultures of beneficial microorganisms that help in enhancing plant growth and improving soil health. Examples include Trichoderma spp. and Bacillus spp.
Plant Growth-Promoting Rhizobacteria (PGPR): These bacteria help in promoting plant growth by various mechanisms like nitrogen fixation, phosphorus solubilization, and production of plant growth hormones. Examples include Pseudomonas spp. and Bacillus spp.
Types of Biofertilizers
Symbiotic Nitrogen-Fixing Bacteria: Rhizobium is a vital symbiotic nitrogen-fixing bacteria that form a mutually beneficial relationship with plants, providing fixed nitrogen to them.
Loose Association of Nitrogen-Fixing Bacteria: Azospirillum is a type of nitrogen-fixing bacteria that live around the roots of higher plants without forming an intimate relationship with the plants. They collect plant exudates for food in a process known as associative mutualism.
Symbiotic Nitrogen-Fixing Cyanobacteria: Blue-Green algae or Cyanobacteria form symbiotic associations with various plants like liverworts, cycad roots, ferns, and lichens. Anabaena, found in fern leaf cavities, is responsible for nitrogen fixation.
Free-Living Nitrogen-Fixing Bacteria: These are free-living soil bacteria that perform nitrogen fixation independently. Examples include Clostridium beijerinckii and Azotobacter.
Among these types, Rhizobium and Azospirillum are the most widely used biofertilizers.
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