1. Biofertilizers are microbial inoculants that help improve soil fertility by fixing nitrogen, solubilizing phosphorus, or decomposing organic matter. They are environmentally friendly alternatives to chemical fertilizers. 2. There are several types of biofertilizers including nitrogen fixers, phosphate solubilizers, mycorrhizal fungi, and plant growth promoters. Nitrogen fixers include bacteria that live freely or in association with plants. 3. Production of biofertilizers involves selecting efficient microbial strains, growing them in culture, mixing them with carriers like peat, and packaging the inoculants for storage and application to seeds or soil. Maintaining viability and following quality standards is important

1. Biofertilizers and their production

2. Biofertilizers are carrier-based microbial inoculants containing sufficient cells of efficient strains
of specific microoranisms, that help in enhancing the soil fertility by fixing atmospheric nitrogen,
solubilization/ mineralization of phosphorus or decomposing organic wastes, by augmenting
plant growth promoting substances with their biological activities.
Biofertilizers

3. Characteristicsof Biofertilizers
• They are reasonable and nature friendly fertilizers which contain microbial inoculants of
algae, fungi and bacteria either alone or in combination.
• Highly suggested for improving soil fertility and health. • They are easily applicable and do
not require any extra proficiency.
• They require in less quantity in comparison to synthetic fertilizers.
• They help in enrichment of soil through micro- flora build up

4. Types of biofertilizers (on the bases of nature and function)
1. Nitrogen fixing: Nitrogen is most abundant and ubiquitous in the air, yet becomes a limiting nutrient due to difficulty
of its fixation and uptake by the plants. However, certain microorganisms, some of which can form various
associations with plants as well, are capable of considerable nitrogen fixation. These microbes can be:-
- Bacteria
• Free living: Free-living in the soil eg. Azotobacter
• Associative: Living in rhizosphere (associative/associated) without endophytic symbioses. Eg. Azospirillum
• Symbiotic: Having symbiotic and other endophytic associations with plants. Eg. Rhizobia, Frankia
- Blue grean algae (Cyanobacteria): have been reported to be helpful in enhancing rice-field fertility for the
cultivation of rice in many parts of the world. BGA can further provide natural growth hormones, 172
proteins, vitamins, and minerals to the soil. Eg. Anabaena, Nostoc, Tolypothrix, Cylindrospermum etc.
- Azolla: is a floating pteridophyte, which contains as endosymbiont the nitrogenfixing cyanobacterium Anabaena
azollae. Azolla is either incorporated into the soil before rice transplanting or grown as a dual crop along with rice.

5. 2. Phosphate solubilizing: The phosphorus-solubilizing bacteria (PSB) can increase phosphorus availability to
plants by dissolution of bound phosphates in soil by secreting organic acids characterized by lower pH in their
vicinity. Eg. Bacillus spp., Paenibacillus spp., Pseudomonas spp. etc.
3. Phosphate mobilizing: The mycorrhizal fungi form obligate or facultative functional mutualistic symbioses
with more than 80% of all land plants, in which the fungus is dependent on host for photosynthates and energy
and in return provides a plethora of benefits to its host. The mycelium of the fungus extends from host plant
root surfaces into soil, thereby increasing the surface area for more efficient nutrient access and acquisition for
the plant, especially from insoluble phosphorus sources and others like calcium, copper, zinc, etc, eg.
ectomycorrhiza (Laccaria spp., Pisolithus spp., Boletus spp., Amanita spp.), endomycorrhiza (eg. arbuscular
mycorrhiza- Glomus sp., Gigaspora sp., Acaulospora sp., Scutellospora sp., and Sclerocystis sp.)

6. 4. Mineral-Solubilizing Biofertilizers – Potassium solubilizing: Certain rhizobacteria can solubilize insoluble
potassium forms, which is another essential nutrient necessary for plant growth. Eg. Bacillus edaphicus, B.
mucilaginosus, and Paenibacillus glucanolyticus – Silicate and zinc solubilizing: Another important mineral is zinc,
which is present at a low concentration in the Earth’s crust, due to which it is externally applied as the costlier
soluble zinc sulfate to overcome its deficiencies in plant. Certain microbes can solubilize insoluble cheaper zinc
compounds like zinc oxide, zinc carbonate, and zinc sulfide in soil. Similarly, microorganisms can hydrolyze silicates
and aluminum silicates by supplying protons (that causes hydrolysis) and organic acids. Eg. Bacillus subtilis,
Thiobacillus thioxidans, and Saccharomyces sp.
5. Plant growth promoting rhizobacteria: Besides nitrogen-fixing, phosphorus and minerals solubilizing microbes,
there are microbes that are suitable to be used as biofertilizers as these enhance plant growth by synthesizing
growth-promoting chemicals like growth hormones (auxins, gibberellin etc.). These bacteria shows more than one
mechanism of plant growth promotion viz. nitrogen fixation, phosphorus solubilization, production of antibiotics,
cytokinins, chitinase, and other hydrolytic enzymes and enhancement of soil porosity. Eg. Achromobacter,
Alcaligenes, Arthrobacter, Actinoplanes, Azotobacter, Bacillus, Pseudomonas fluorescens, Rhizobium,
Bradyrhizobium etc.

7. 6. Compost Biofertilizers: Compost is a decomposing, brittle, murky material forming a symbiotic food web within the soil,
which contains about 2% (w/w) of nitrogen, phosphorus, and potassium, along with microorganisms, earthworms, and dung
beetles.
• The microbial organic solid residue oxidation causes the formation of humuscontaining material, which can be used as an
organic fertilizer that sufficiently aerates, aggregates, buffers, and keeps the soil moist, besides providing beneficial minerals
to the crops and increasing soil microbial diversity.
• Compost is produced from a wide variety of materials like straw, leaves, cattleshed bedding, fruit and vegetable wastes,
biogas plant slurry, industrial wastes, city garbage, sewage sludge, factory waste, etc.
• The compost is formed from these materials by different decomposing microorganisms like Trichoderma viridae, Aspergillus
niger, A. terreus, Bacillus spp., several Gram-negative bacteria (Pseudomonas, Serratia, Klebsiella, and Enterobacter), etc. that
have plant cell wall-degrading cellulolytic or lignolytic and other activities, besides having proteolytic activity and antibiosis
(by production of antibiotics) that suppresses other parasitic or pathogenic microorganisms .
• Another important type (vermicompost) contains earthworm cocoons, excreta, microorganisms (like bacteria,
actinomycetes, fungi), and different organic matters, which provide nitrogen, phosphorus, potassium, and several
micronutrients, and efficiently recycles animal wastes, agricultural residues, and industrial wastes costeffectively and uses low
energy

8. Biofertilizer Production
• Biofertilizers are the biological preparations with live dormant strains of microbes, which positively impact
soil rhizosphere and helps in plant development. Biofertilizers are formulated with living or dormant (inactive
metabolically) microbial cells. An efficient nitrogen-fixing strain is selected, and later the inoculum is prepared to
produce a bio-fertilizer of good quality.
• An inoculum is a form in which the strain is inoculated in the seed or soil. Besides strain selection, maintenance,
storage and packing are other aspects of bio-fertilizer production. During the biofertilizer production, the product
manufactured must fulfil the quality standards laid down by BIS

9. Production of biofertilizer
Commercial Production:
To produce inoculum, you must inoculate the isolated strain in small
flasks containing a suitable medium. The starter culture should have
a volume that must produce at least 1×109 cells/ml. Then, add
culture to the carrier for the preparation of bio-inoculant.
Carriers carry nitrogen-fixing organisms. Primarily, sterilize the
carrier and then inoculate it into the seed or soil. But in a few cases,
the carrier is inoculated first and later subjected to sterilization via
UV irradiation. Then, package the inoculum or biofertilizer with a
standard quantity of 109-1010 viable cells/gram.
As per the quality standards, the final moisture content of the
biofertilizer must be 40-60%. For large scale biofertilizer production,
use large culture fermenters rather than big flasks. The production
process of biofertilizer includes the following sequential steps:

10. Strain Selection
First, select the efficient nitrogen-fixing strains and later maintain the culture of strains artificially in the laboratory on the
nutrient-rich medium before inoculating them in the seed or soil.
Seed Pelleting
Then, prepare the inoculum of the desired strain. After that, inoculate the seeds using either of the seed coating
methods (direct coating or slurry method). The direct seed coating method uses gum arable or sugary syrup. The slurry
seed coating method uses efficient nitrogen-fixing strains (coating of rhizobia over specific host legume seeds).
Then, add calcium carbonate to the sticky seeds right away after seed coating. Sometimes, root nodule bacteria are
absent in soil, necessary to fulfil the plant’s nitrogen requirements. Therefore, we should inoculate the soil with
inadequate nodule bacteria with seed pellets of highly effective rhizobia.
Inoculant Carriers
Inoculants are simply the mixture of the starter culture and a finely milled carrier material. The ideal properties
of the carrier should have the properties:
•Non-toxicity
•Good moisture absorption capacity
•Free of lump forming material
•Easy to sterilize
•Inexpensive
•Easily available
•Good buffering capacity

11. Therefore, the carrier material with these properties can prolong the growth of microbial strains. Peat is the most standard carrier
used in bioinoculant preparation. The application of peat is not common in few countries such as India due to its unavailability.
Therefore, peat as a carrier can be substituted with various alternative carriers like lignite, coal, charcoal, vermiculite,
polyacrylamide etc. The production of inoculant involves carrier processing, in which the carrier material is subjected to the
following stages:
•Mining: Carrier like peat is mined, drained and cleared off stones, roots, etc.
•Drying: Then, the carrier material is shredded and dried.
•Milling: After that, pass the peat through heavy mills. Peat is generally used as a soil inoculant, with a preferable particle size
(0.5-1.5 mm).
•Neutralization: Then, neutralize the carriers by treating them with precipitated CaCO3, which maintains the pH between 6.5 and
7.0.
•Sterilization: At last, sterilize the carriers so that they can be used as inoculants.
Quality Standards for Inoculants
During the production of biofertilizers, it should be kept in mind that the product must make up the quality standards. The
inoculant should be carrier-based. There should be a minimum of 108 viable cells per gram (dry mass) of the carrier in the
inoculant. The inoculant must have an expiry period of at least 12 months from DOM.

12. Packaging
Finally, pack the bio-inoculant in polyethene bags of low density (50-75 µ). Label each packet with the product
information like name of the product, type of carrier, batch number, DOM, DOE, net quantity and storage instructions
etc. Each packet should be ISI (BIS) certified.
Storage
Store the bio-inoculant in a cool and dry place. Keep the bio-inoculant ideally at a temperature of 15°C and a pH
between 6.0 and 7.5.
Inoculation into the Field
Seed inoculation and soil inoculation are the two standard inoculation methods that are prevalently used. The soil
inoculation involves direct mixing of the bio-inoculant into the sowing furrow along with the seeds. Seed inoculation is
a more popular technique that involves seed pelleting or coating with an inoculant.