Biofertilizers - Types & their application

'Biofertilizer' is a substance which contains living microorganism 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.Biofertilizers are not fertilizers. Fertilizers directly increase soil fertility by adding nutrients. 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 grouped in different ways based on their nature and function.

S. No.




N2  fixing Biofertilizers



  Azotobacter, Clostridium,  Anabaena, Nostoc,



  Rhizobium, Frankia, Anabaena azollae


  Associative Symbiotic



P Solubilizing Biofertilizers



  Bacillus megaterium var. phosphaticum

  Bacillus circulans, Pseudomonas striata



  Penicillium sp, Aspergillus awamori


P Mobilizing Biofertilizers


  Arbuscular mycorrhiza

  Glomus sp.,Gigaspora sp.,Acaulospora sp.,

  Scutellospora sp. & Sclerocystis sp.



  Laccaria sp., Pisolithus sp., Boletus sp., Amanita sp.


  Orchid mycorrhiza

  Rhizoctonia solani


Biofertilizers for Micro nutrients


  Silicate and Zinc solubilizers

  Bacillus sp.


Plant Growth Promoting Rhizobacteria



  Pseudomonas fluorescens


Different types of biofertilizers:

1. Rhizobium - This belongs to bacterial group and the classical example is symbiotic nitrogen fixation. The bacteria infect the legume root and form root nodules within which they reduce molecular nitrogen to ammonia which is reality utilized by the plant to produce valuable proteins, vitamins and other nitrogen containing compounds. The site of  symbiosis is within the root nodules. It has been estimated that 40-250 kg N / ha / year is fixed by different legume crops by the microbial activities of Rhizobium. Table shows the N fixation rates.

Table: Quantity of biological N fixed by Liqiud Rhizobium in different crops

Host Group

Rhizobium Species


N fix kg/ha

Pea group


  Rhizobium leguminosarum

  Green pea, Lentil

62- 132

Soybean group




57-  105

Lupini Group


  R. lupine orinthopus


70- 90

Alfafa grp.Group


  R.mellilotiMedicago Trigonella


100- 150

Beans group


  R. phaseoli


80- 110

Clover group


  R. trifoli



Cowpea group


  R. species

  Moong, Redgram, 
  Cowpea, Groundnut

57- 105

Cicer group


  R. species

  Bengal gram

75- 117

2.  Azotobacter - It is the important and well known free living nitrogen fixing aerobic bacterium. It is used as a Bio-Fertilizer for all non leguminous plants especially rice, cotton, vegetables etc. Azotobacter cells are not present on the rhizosplane but are abundant in the rhizosphere region. The lack of organic matter in the soil is a limiting factor for the proliferation of Azotobaceter in the soil.

3. Azospirillum- It belongs to bacteria and is known to fix the considerable quantity of nitrogen in the range of 20- 40 kg N/ha in the rhizosphere in non- non-leguminous plants such as cereals, millets, Oilseeds, cotton etc.

4. Cyanobacteria- A group of one-celled to many-celled aquatic organisms. Also known as blue-green algae                                                                                                                                          

5. Azolla -  Azolla is a free-floating water fern that floats in water and fixes atmospheric nitrogen in association with nitrogen fixing blue green alga Anabaenaazollae. Azolla fronds consist of sporophyte with a floating rhizome and small overlapping bi-lobed leaves and roots. Azolla is considered to be a potential biofertilizer in terms of nitrogen contribution to rice. Long before its cultivation as a green manure, Azolla has been used as a fodder for domesticated animals such as pigs and ducks. In recent days, Azolla is very much used as a sustainable feed substitute for livestock especially dairy cattle, poultry, piggery and fish

6. Phosphate solubilizing microorganisms(PSM)

7. AM fungi- An arbuscular mycorrhiza (AM Fungi) is a type of mycorrhiza in which the fungus penetrates the cortical cells of the roots of a vascular plant.

8. Silicate solubilizing bacteria (SSB)- Microorganisms are capable of degrading silicates and aluminum silicates. During the metabolism of microbes several organic acids are produced and these have a dual role in silicate weathering.

9. Plant Growth Promoting Rhizobacteria (PGPR)-The group of bacteria that colonize roots or rhizosphere soil and beneficial to crops are referred to as plant growth promoting rhizobacteria (PGPR).


Liquid Biofertilizers


The advantages of Liquid Bio-fertilizer over conventional carrier based Bio-fertilizers are listed below:-

  • Longer shelf life -12-24 months.                                               
  • No contamination.
  • No loss of properties due to storage upto 45º c.
  • Greater potentials to fight with native population.
  • Easy identification by typical fermented smell.
  • Better survival on seeds and soil.
  • Very much easy to use by the farmer.
  • High commercial revenues.
  • High export potential.

Characteristics of different liquid Bio-fertilizers


Physical features of liquid Rhizobium:

  • Dull white in colour
  • No bad smell
  • No foam formation, pH 6.8-7.5


Physical  features of liquid Azospirillum:

  • The colour of the liquid may be blue or dull white.
  • Bad odours confirms improper liquid formulation and may be concluded as mere broth.
  • Production of yellow gummy colour materials comfirms the quality product.
  • Acidic pH always confirms that there is no Azospirillum bacteria in the liquid.

Role of Liquid Azospirillumunder field conditions:

  • Stimulates growth and imparts green colour which is a characteristic of a healthy plant.
  • Aids utilization of potash, phosphorous and other nutrients.
  • Encourage plumpness and succulence of fruits and increase protein percentage.


Physical features of liquid Azotobacter:

The pigmentation that is produced by Azotobacter in aged culture is melanin which is due to oxidation of tyrosine by tyrosinase an enzyme which has copper. The colour can be noted in liquid forms. Some of the pigmentation are described below-

  • A. chroococcum: Produces brown-black pigmentation in liquid inoculum.
  • A. beijerinchii: Produces yellow- light brown pigementation in liquid inoculum
  • A. vinelandii: Produces green fluorescent pigmentation in liquid inoculum.
  • A. paspali: Produces green fluorescent pigmentation in liquid inoculum.
  • A. macrocytogenes: Produces, pink pigmentation in liquid inoculum.
  • A. insignis: Produces less, gum less, grayish-blue pigmentation in liquid inoculum.
  • A. agilies: Produces green-fluorescent pigmentation in liquid inoculum.


This is a sacharophillic bacteria and associate with sugarcane, sweet potato and sweet sorghum plants and fixes 30 kgs/ N/ ha year. Mainly this bacterium is commercialized for sugarcane crop. It is known  to increase yield by 10-20 t/ acre and sugar content by about  10-15 percent.

Liquid  Bio-fertlizer application methodology-

There are three ways of using Liquid Bio-fertilizers

  1. Seed treatment
  2. Root dipping
  3. Soil application


Dosage of liquid Bio-fertilizers in different crops

Recommended Liquid Bio-fertilizers and its application method, quantity to be used for different crops are as follows:






Quantity to be used

Field crops


Seed treatment


200 ml/ acre



Chickpea, pea, Groundnut, soybean, beans, Lentil, lucern, Berseem, Green gram, Black gram, Cowpea and pigeon pea




Seed treatment

200 ml/ acre

Wheat, oat, barley




Seed treatment

200 ml/ acre

Oil seeds


Seed treatment

200 ml/ acre

Mustard, seasum, Linseeds, Sunflower, castor




Seed treatment

200 ml/ acre

Pearl millets, Finger millets, kodo millet


Maize and Sorghum


Seed treatment

200 ml/ acre

Forage crops and Grasses


Seed treatment

200 ml/ acre

Bermuda grass, Sudan grass, Napier Grass , ParaGrass, StarGrass etc.


Other Misc. Plantation Crops


Seedling treatment

500 ml/ acre



Tea, Coffee


Soil treatment

400 ml/ acre

Rubber, Coconuts


Soil treatment

2-3 ml/ plant

Agro-ForestRY/Fruit Plants


Soil treatment

2-3 ml/plant at nursery

All fruit/agro-forestry (herb,shrubs, annuals and perennial) plants for fuel wood fodder,fruits,gum,spice,leaves,flowers,nuts and seeds puppose

Leguminous plants/ trees


Soil treatment

1-2 ml/ plant



Application of Biofertilizers

1. Seed treatment or seed inoculation 
2. Seedling root dip 
3. Main field application

Seed treatment

One packet of the inoculant is mixed with 200 ml of rice kanji to make a slurry. The seeds required for an acre are mixed in the slurry so as to have a uniform coating of the inoculant over the seeds and then shade dried for 30 minutes. The shade dried seeds should be sown within 24 hours. One packet of the inoculant (200 g) is sufficient to treat 10 kg of seeds.

Seedling root dip

This method is used for transplanted crops. Two packets of the inoculant is mixed in 40 litres of water. The root portion of the seedlings required for an acre is dipped in the mixture for 5 to 10 minutes and then transplanted.

Main field application

Four packets of the inoculant is mixed with 20 kgs of dried and powdered farm yard manure and then broadcasted in one acre of main field just before transplanting.

Rhizobium :- For all legumes Rhizobium is applied as seed inoculant.

Rhizobium (only seed application is recommended)

S. No.


Total requirement of packets per ha























In the transplanted crops, Azospirillum is inoculated through seed, seedling root dip and soil application methods. For direct sown crops, Azospirillum is applied through seed treatment and soil application.


  • Bacterial inoculants should not be mixed with insecticide, fungicide, herbicide and fertilizers.
  • Seed treatment with bacterial inoculant is to be done at last when seeds are treated with fungicides.

Constraints in Biofertilizer Technology

Though the biofertilizer technology is a low cost, ecofriendly technology, several constraints limit the application or  implementation of the technology the constraints may be environmental, technological, infrastructural, financial, human resources, unawareness, quality, marketing, etc. The different constraints in one way or other affecting the technique at production, or marketing or usage.

Technological constraints

  • Use of improper, less efficient strains for production.
  • Lack of qualified technical personnel in production units.
  • Production of poor quality inoculants without understanding the basic microbiological techniques
  • Short shelf life of inoculants.

Infrastructural constraints

  • Non-availability of suitable facilities for production
  • Lack of essential equipments, power supply, etc.
  • Space availability for laboratory, production, storage, etc.
  • Lack of facility for cold storage of inoculant packets

Financial constraints

  • Non-availability of sufficient funds and problems in getting bank loans
  • Less return by sale of products in smaller production units.

Environmental constraints

  • Seasonal demand for biofertilizers
  • Simultaneous cropping operations and short span of sowing/planting in a particular locality
  • Soil characteristics like salinity, acidity, drought, water logging, etc.

Human resources and quality constraints

  • Lack of technically qualified staff in the production units.
  • Lack of suitable training on the production techniques.
  • Ignorance on the quality of the product by the manufacturer
  • Non-availability of quality specifications and quick quality control methods
  • No regulation or act on the quality of the products
  • Awareness on the technology
  • Unawareness on the benefits of the technology
  • Problem in the adoption of the technology by the farmers due to different methods of inoculation.
  • No visual difference in the crop growth immediately as that of inorganic fertilizers.

Authors: Himachal Motghare and Rashmi Gauraha O/o Dy.Director of Agriculture,