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A biofertilizer (also bio-fertilizer) is a substance which contains living microorganisms which, when applied to seeds, plant surfaces, or soil, colonize the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant. Biofertilizers add nutrients through the natural processes of nitrogen fixation, solubilizing phosphorus, and stimulating plant growth through the synthesis of growth-promoting substances. Biofertilizers can be expected to reduce the use of synthetic fertilizers and pesticides. The microorganisms in biofertilizers restore the soil's natural nutrient cycle and build soil organic matter. Through the use of biofertilizers, 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). Therefore, they are extremely advantageous in enriching soil fertility and fulfilling plant nutrient requirements by supplying the organic nutrients through microorganism and their byproducts. Hence, biofertilizers do not contain any chemicals which are harmful to the living soil.
Biofertilizers provide "eco-friendly" organic agro-input. Biofertilizers such as Rhizobium, Azotobacter, Azospirilium and blue green algae (BGA) have been in use a long time. Rhizobium inoculant is used for leguminous crops. Azotobacter can be used with 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 belonging to a general cyanobacteria genus, Nostoc or Anabaena or Tolypothrix or Aulosira, fix atmospheric nitrogen and are used as inoculations for paddy crop grown both under upland and low-land conditions. Anabaena in association with water fern Azolla contributes nitrogen up to 60 kg/ha/season and also enriches soils with organic matter.
Other types of bacteria, so-called 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. In fact, due to immobilization of phosphate by mineral ions such as Fe, Al and Ca or organic acids, the rate of available phosphate (Pi) in soil is well below plant needs. In addition, chemical Pi fertilizers are also immobilized in the soil, immediately, so that less than 20 percent of added fertilizer is absorbed by plants. Therefore, reduction in Pi resources, on one hand, and environmental pollutions resulting from both production and applications of chemical Pi fertilizer, on the other hand, have already demanded the use of phosphate-solubilizing bacteria or phosphate biofertilizers.
Benefits of biofertilizers are:
- These are means of fixing the nutrient availability in the soil.
- Since a bio-fertilizer is technically living, it can symbiotically associate with plant roots. Involved microorganisms could readily and safely convert complex organic material into simple compounds, so that they are easily taken up by the plants. Microorganism function is in long duration, causing improvement of the soil fertility. It maintains the natural habitat of the soil. It increases crop yield by 20-30%, replaces chemical nitrogen and phosphorus by 30%, and stimulates plant growth. It can also provide protection against drought and some soil-borne diseases.
Some important groups of biofertilizers include:
- Azolla-Anabena symbiosis: Azolla is a small, eukaryotic, aquatic fern having global distribution.Prokaryotic blue green algae Anabena azolla resides in its leaves as a symbiont. Azolla is an alternative nitrogen source. This association has gained wide interest because of its potential use as an alternative to chemical fertilizers.
- Rhizobium: Symbiotic nitrogen fixation by Rhizobium with legumes contribute substantially to total nitrogen fixation. Rhizobium inoculation is a well-known agronomic practice to ensure adequate nitrogen
- Vessey, J. Kevin (2003). "Plant growth promoting rhizobacteria as biofertilizers". Plant and Soil. 255 (2): 571. doi:10.1023/A:1026037216893.
- "Listing 17 bio-fertilizer microbes and their effects on the soil and plant health functions". Explogrow. 15 June 2016.
- http://eprints.ru.ac.za/36/1/Kiguli.PDF[dead link]
- Malboobi, Mohammad Ali; Behbahani, Mandana; Madani, Hamid; Owlia, Parviz; Deljou, Ali; Yakhchali, Bagher; Moradi, Masoud; Hassanabadi, Hassan (2009). "Performance evaluation of potent phosphate solubilizing bacteria in potato rhizosphere". World Journal of Microbiology and Biotechnology. 25 (8): 1479. doi:10.1007/s11274-009-0038-y.
- Pandey, Anita; Trivedi, Pankaj; Kumar, Bhavesh; Palni, Lok Man S (2006). "Characterization of a Phosphate Solubilizing and Antagonistic Strain of Pseudomonas putida (B0) Isolated from a Sub-Alpine Location in the Indian Central Himalaya". Current Microbiology. 53 (2): 102. doi:10.1007/s00284-006-4590-5. PMID 16832725.