Bio-fertilizers are ready to use live formulates of such beneficial micro-organisms which on application to seed, root or soil mobilize the availability of nutrients by their biological activity in particular, and help build up the micro-flora and in turn the soil health in general.
Biofertilizers have an important role to play in improving nutrient supplies and their crop availability in the years to come. They are of environment friendly, non-bulky and low cost agricultural inputs. Some specific bacteria or micro-organisms in the soil convert nitrogen into ammonia and amino acids. These amino acids can be used by plants to build up proteins. The process is called “biological nitrogen fixation” and the product is called biofertilizers. A biofertilizer is an organic product containing a specific micro-organism in concentrated form which is derived either from the plant roots or from the soil root zone (Rhizosphere).
1.Nitrogen Fixing Bacteria (NFB)
a) Symbiotically by Rhizobium
b) Non symbiotically by Azatobactor, Azospirillum
2.Phosphorous Solubilizing Bacteria (PSB)
3.Potassium Mobilizing Micro-organism (Frateuria aurentia).
In recent years, a need has arisen for organic fertilizers including bio-fertilizers to minimize our dependence on fertilizer nitrogen, phosphorous and potassium.Water based formulations have rarely been marketed, except in developing countries like India, because of the difficulty of curbing growth of contaminants in less pure preparations. Growth is easily arrested by drying in wettable powders. However, currently, there is more interest in developing liquid concentrates with multi-bacteria for market.
Rhizobium :It is a symbiotic nitrogen fixer which assimilates atmospheric nitrogen and fixes in the root nodules, formed in the roots of leguminous plants. They produce enzymes which reduce the molecular nitrogen to ammonia which is readily utilized by plants. Rhizobium can fix 50-200 kgs N/ha in one crop season and can leave behind substantial quantities of about 20-30 kgs N/ha for the succeeding crop.
Azotobacter: This group of bacteria is free living nitrogen fixer. The plants inoculated with Azotobacter, derive possible benefits in terms of increased grain, plant biomass and nitrogen uptake which in turn are attributed to increase in nitrogen input from biological nitrogen fixation, development and branching of roots., production of plant growth hormones, vitamins, enhancement in uptake of K and Fe, improved water status of the plant and increased anti-fungal compounds.
Azospirillum : It is an associative micro-aerophilic nitrogen fixer. It colonizes the root mass and in an environment of low oxygen tension. These bacteria induce the plant roots to secrete a mucilage which aerates low oxygen environment and helps to fix atmospheric nitrogen. High nitrogen fixation capacity, low energy requirement and abundant establishment in the roots of plants and tolerance to high soil temperature make these most suitable for tropical condition. Azospirillum can be used under saline-alkaline conditions because they are known to maintain high nitrogen activities under such stress conditions.
Phosphorous Solubilizing Bacteria (PSB): Indian soils are generally low to medium in available phosphate. Not more than 30% of the applied phosphate is available to the current crop, remaining part gets converted into relatively unavailable form. Bacteria likeBacillus megatherium, Bacillus polymyxa, Pseudomonas strata, Pseudomonas rathonisposses the ability to solubilize insoluble phosphate to soluble form by secreting organic acids. These organic acids lower soil Ph and in turn brings about dissolution of unavailable forms of soil phosphorous. Some of the hydroxyl acids chelate Ca, Al, Fe and Mg resulting in effective availability in soil. Its inoculation as bio-fertilizer reduces the phosphate dose by 50% and could be applied in the form of rock phosphate which is the cheaper source of phosphorous.
Potash Mobilizing Bacteria ( Frateuria aurentia):
Use of K-Bacteria releases some of the gorged potassium between the layers of clay. The potash mobilizing bacteria is gram negative rod type bacteria, can grow in Ph 3.5 to11 and capable of mobilizing the mineral potash to the tune of 40-60 kg per ha.