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BIOFERTILIZERS. NITROGEN-FIXERS. Addition of Nitrogen to the soil Chemical fertilizers Biological nitrogen fixation (BNF) Chemical fertilizers: Pollution & soil contamination So, Biofertilizers / “Microbial inoculants” 100% natural and organic .

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  • Addition of Nitrogen to the soil

    • Chemical fertilizers

    • Biological nitrogen fixation (BNF)

  • Chemical fertilizers: Pollution & soil contamination

  • So, Biofertilizers / “Microbial inoculants”

  • 100% natural and organic


  • A large population of a specific / group of beneficial microorganisms for enhancing the productivity of soil either

    • by fixing atmospheric nitrogen or by solubilising soil phosphorus or

    • by stimulating plant growth through synthesis of growth promoting substances.

  • Main sources: Bacteria, fungi & cyanobacteria (blue-green algae)

  • Symbiotic relationship with plants


  • End product of the various phases of Biodigestion has humus in it. 

  • Pure Biofertilizer, and it can be

    • Used on soil as a high quality organic fertilizer

    • Used as a corrector of pH

    • Has a high nutrient concentration and can be used directly over soil before planting.

  • Diluted Biofertilizer.


  • Soil microbes used in biofertilizers are:

    • Phosphate Solubilizing microbes,

    • Mycorrhizae,

    • Azospirillum,

    • Azotobacter,

    • Rhizobium,

    • Sesbania,

    • Blue Green Algae, and

    • Azolla.

Phosphate solubilizing microbes

Phosphate-solubilizing Microbes:

  • Phosphorus, important nutrient for plants

  • Microbes that can solubilize the cheaper sources of P – as rock phosphate.

    • Bacteria – Pseudomonas striata & Bacillus megaterium

    • Fungi – Aspergillus & Penicillium


  • By secretion of organic acids

  • Also, releases soluble Pi into soil through decomposition of phosphate-rich organic compounds.

  • Usually, microbes inoculated to coffee husk along with rock phosphate while preparing compost.



  • Refers to fungus associated with plant roots.

  • 2 types:

    • Ectotrophic and

    • Endotrophic


  • Important for adequate uptake of immobile ions such as phosphate, zinc and micronutrients

  • Stimulates branching of the root

  • Increases the absorption surface of the root.

  • Tolerance to drought, high soil temperature, soil toxins, and extreme pH levels

  • Protection against root pathogens



  • Nitrogen-fixing bacteria that lives in a symbiotic relationship in the root cortex of several tropical crops

  • Stimulate plant growth through N2 fixation

  • Helps in production of growth substances like auxins, gibberellins and cytokinins.

  • 10-15% of the required N2 is met by Azospirillum biofertilizer.



  • Triple action

  • Free-living, N2-fixing bacteria

  • Produces several plant growth promoting substances.

  • Protects plants against pathogenic microbes either by discouraging their growth or by destroying them – BIOCONTROL.




  • Gram negative, motile, non-sporulating rods.

  • Forms root nodules in leguminous plants (Fabaceae) & fix atmospheric N2 (diazotrophy) in a symbiotic association


  • Legumes: Peas, beans, clover, and soy

  • Rhizobia enter a root hair and travel down a tube to a relatively anoxic centre of the root hair cell.

  • Here, proliferating plant cells form a nodule.

  • Bacteria differentiate into bacteroids

  • Fixes N2 from atmosphere into a plant usable form, ammonium (NH4+), utilising the enzyme nitrogenase

  • Plant supplies carbohydrates, proteins, sufficient O2, malate and succinate to bacteria





  • A genus from the family Fabaceae with some aquatic species

  • A green manure plant which forms both root and stem nodules in association with rhizobium and so, fixes more atmospheric N2

  • Produce 10 times more nodules than other legumes

  • Have a very high capacity to fix atmospheric N2


  • Grown & turned into the soil while still green to enrich soil N2

    • Enriches concentration of Ca, P, S & micronutrients.

  • Notable species

    • Rattlebox (Sesbania drummondii),

    • Spiny Sesbania (Sesbania bispinosa), and

    • Sesbania grandiflora (an edible plant)

Blue green algae

Blue Green Algae

  • or Cyanobacteria

  • Can carry out both photosynthesis as well as N2 fixation

  • Algal flakes are grown & then broadcasted.




  • Mosquito fern / Duckweed fern / Fairy moss / Water fern)

  • A genus of 7 species of aquatic ferns

  • A floating fern, harbouring a blue green algae in its leaf cavities.

  • Form a symbiotic relationship with the blue-green alga Anabaena azollae, that fixes atmospheric N2

  • Can grow at great speed - doubling its biomass every 2-3 days

  • Then, harvested, dried and used as biofertilizer

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