A biofertilizer (also bio-fertilizer) is defined as a substance which contains living microorganisms which, when applied to seed, plant surfaces, or soil, colonizes the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant.
Plants have a symbiotic relationships with fungi, bacteria, and algae, the most common of which are with mycorrhiza, rhizobium, and cyanophyceae. These are known to deliver a number of benefits including plant nutrition, disease resistance, and tolerance to adverse soil and climatic conditions.
Bio-fertilizers add nutrients through the natural processes of nitrogen fixation, solubilizing phosphorus, and stimulating plant growth through the synthesis of growth-promoting substances.
Rhizobium, Azotobacter, Azospirillum and blue green algae (BGA) have been in use a long time.
Azotobacter species are used for the cultivation of crops like wheat, maize, mustard, cotton, potato and other vegetable crops.
Azospirillum inoculations are recommended mainly for sorghum, millets, maize, sugarcane and wheat.
Blue green algae fix atmospheric nitrogen and are used as inoculations for paddy crop.
The phosphate-solubilizing bacteria, such as Pantoea agglomerans strain P5 or Pseudomonas putida strain P13, are able to solubilize the insoluble phosphate from organic and inorganic phosphate sources .These strains are of immense use in ecological and environmental point of view . Due to mineral ions such as Fe, Al and Ca or organic acids, immobilization of phosphate occurs and the rate of available phosphate (Pi) in soil is well below plant needs. Excess use of chemical Pi fertilizers are also immobilized in the soil ultimately less than 20 percent of added fertilizer is absorbed by plants. Therefore, to reduce phosphate resources and environmental pollutions( resulting from both production and applications of chemical Pi fertilizer) phosphate-solubilizing bacteria or phosphate bio-fertilizers are very inevitable.
Through the use of bio-fertilizers, healthy plants can be grown, while enhancing the sustainability and the health of the soil. Since they play several roles, a preferred scientific term for such beneficial bacteria is "plant-growth promoting rhizobacteria" (PGPR).
Since a bio-fertilizer is technically living, it can symbiotically associate with plant roots. Involved microorganisms could readily and safely convert complex organic material in simple compounds, so that plants can assimilate those nutrients easily .
Microorganism in biofertilizers symbiotic function causes improvement of the soil fertility.
Bio-fertilizers are cost-effective relative to chemical fertilizers. They have lower manufacturing costs, especially regarding nitrogen and phosphorus use that’s why it is farmers and cultivators friendly .
Biofertilizers also provide protection against drought and some soil-borne diseases and hence it may be defined as the panacea of green eco friendly .
It increases crop yield by 20-30%, replaces chemical nitrogen and phosphorus by 25%, and stimulates plant growth without altering the physical and chemical characteristics of the Soil .