Introduction :
A bio fertilizer is simply a substance which contains living microorganisms which when applied to the soil, a seed or
plant surface colonize the rhizosphere and promotes growth by increasing the supply or availability of nutrients to the host plant.
“ Bio fertilizer is a modernized form of organic fertilizer into which beneficial microorganisms have been incorporated ”
The production of bio fertilizer involves three biochemical steps which includes the breaking down of complex materials into smaller substances in a process known as anaerobic digestion. Three stage include :
Step - 1 : complex organic matter is broken down by cellulolytic microorganisms to produce simple molecules such as long chain fatty acids and other substances.
Step - 2 : The products from stage one are fermented leading to the production of simpler intermediates such as acetic acids, pyruvic acids, carbon dioxide and so on.
Step - 3 : Methanogens act on the products, giving off a mixture of gases known as biogas.
Bio fertilizer production represented in equation form
Types of Bio Fertilizers :
Biofertilizers add nutrients through the natural processes of fixing atmospheric nitrogen, solubilizing phosphorus and stimulating plant growth through the synthesis of growth-promoting substances. They can be categorised in different ways based on their nature and function.
1. Nitrogen fixing bio fertilizers
This group fixes nitrogen symbiotically. Nitrogen bio fertilizers help to correct the nitrogen levels in the soil. Nitrogen is a limiting factor for plant growth because plants need a certain amount of nitrogen in the soil to thrive. Different bio fertilizers have an optimum effect for different soils, so the choice of nitrogen bio fertilizer to be used depends on the cultivated crop.
Examples for nitrogen fixing microorganisms are :
(a) Rhizobium are used for legume crops
(b) Azotobacter and Azospirillum for non legume crops
(c) Acetobacter for sugarcane
(d) Azolle for lowland rice paddies
2. Phosphate solubilizing bio fertilizers
Phosphate solubilizing bacteria work by solubilizing the insoluble forms of phosphate in the soil, so that plants can use them. A phosphorus in the soil occurs mostly in insoluble form which cannot be absorbed by plants. Severa bacteria and fungi has ability to conver insoluble phosphate into soluble form by secreting organic acids which lower the pH of the soil and cause the dissolution of bound forms of phosphate making them available to plants.
Unlike nitrogen bio fertilizers, the usage of phosphorus bio fertilizers is not dependent on the crops cultivated on the soil. Phosphate is used for all crops with Rhizobium, Azotobacter, Azospirillum and Acetobacter.
3. Phosphate mobilizing bio fertilizers
They work by scavenging phosphates from soil layers and mobilizing the insoluble phosphorus in the soil to which they are applied. Sometimes Phosphate solubilizing bacteria also acts as phosphate mobilizers bacteria. Examples of phosphate mobilizing bacteria are Mycorrhiza.
The mycorrhiza is a mutually beneficial or symbiotic association of a fungus with the root of a higher plant. The most common fungal partners of mycorrhiza are Glomus species. Mycorrhizal roots show a sparse or dense wooly growth of fungal hyphae on their surface. Root cap and root hairs are absent.
Mycorrhiza is a potential bio fertilizer which mobilizes P, Fe, Zn, B and other trace elements. It supplies moisture from far-off inches and is ideal for long
4. Plant growth promoting bio fertilizers
They work by producing hormones and anti metabolites which promotesroot growth, decomposition of organic matter which helps in mieralization of the soil thereby increasing availability of nutrients and improving crop yield. Example of plant growth promoting bio fertilizer are Pseudomonas
Pseudomonas may be used as bio control agents that reduce disease severity and promote plant growth. They stimulate growth by several mechanisms. The bacteria can produce some compounds that inhibit spread of plant pathogens.
Pseudomonas species thrive under moist conditions in soil (particularly in association with plants), in sewage sediments and the aquatic environments. Environmental conditions which will affect their growth include nutrient availability, moisture, temperature, competition, UV irradiation, oxygen availability, salinity and the presence of inhibitory or toxic compounds, but nutritional demands of Pseudomonas are modest
5. Sulphur oxidizing bio fertilizers
They work by bacterial cell converting the non available sulphur and sulphur related compounds to easily assimilable form of sulphur salts through a process of oxidation. During this process, it brings down the high pH of the soil (alkasol soil). Hence, Symbion-S can be utilized in reclaiming the alkaline and saline soil for normal cultivation. Example of Sulphur oxidizing bio fertilizers are Thiobacillus Thiooxidants
Thiobacillus thiooxidans is an acidophilic, obligately au-totrophic bacterium which derives its energy by oxidizing. reduced or partially reduced sulfur compounds and obtains. its carbon by fixing carbon dioxide from the atmosphere. The strain is able to live in inorganic, acidic environments.
1. Mycorrhizal ( VAM )
Vesicular Arbuscular Mycorrhizal (VAM) fungi possess special structures known as vesicles and arbusculars. VAM fungi are intercellular, obligate endosymbionts and, on establishment on the root system, act as an extended root system. Besides harvesting moisture from deeper and faraway nitches in the soil, they also harvest various micronutrients and provide them to the host plants. VAM facilitates the phosphorus nutrition by not only increasing its availability, but also increasing its mobility. VAM are obligate symbionts and improve the uptake of Zn, Co, P and H2O. Its large-scale application is limited to perennial crops and transplanted crops.
Benefits of Bio Fertilizers
Make nutrients available.
Make the root rhizosphere livelier.
Growth-promoting substances are produced.
More root proliferation.
Better germination.
Improve the quality and quantity of produce.
Improve the fertilizer use efficiency.
Higher biotic and abiotic stress tolerance.
Improve soil health.
Residual effect.
Make the system more sustainable.
Importance of Bio Fertilizers
Bio fertilizers improve soil texture and yield of plants.
They do not allow pathogens to flourish.
They are eco-friendly and cost-effective.
Bio fertilizers protect the environment from pollutants since they are natural fertilizers.
They destroy many harmful substances present in the soil that can cause plant diseases.
Bio fertilizers are proved to be effective even under semi-arid conditions.
Secretion of plant growth hormones which helps in plant growth.
No special care is necessary while using bio fertilizer
Bio fertilizers restore the soil's natural, nutrient cycle and built soil matter.
Bio fertilizer provides protection against drought condition.
Application of Bio Fertilizers
Bio fertilizers are applied during following 3 phase
For seed treatment or seed inoculation
Seeding root dip
Main field application
Bio Fertilizers forms
Bio fertilizers can be applied in form of granules, powder and liquid form
Conclusion
Our dependence on chemical fertilizers and pesticides are becoming life threatening chemicals which are not only hazardous for human consumption but can also disturb the ecological balance. Bio fertilizers can help solve the problem of food need of the ever increasing global population.The application of bio fertilizers containing beneficial microbes promote to a large extent, crop productivity. These potential biological fertilizers would play a key role in productivity and sustainability of soil and protect the environment as eco friendly and cost effective inputs for the farmers.
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