1. BIOFERTILIZERS
NITROGEN-FIXERS

2. 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

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

4. 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.

5. Soil microbes used in biofertilizers are:
Phosphate Solubilizing microbes,
Mycorrhizae,
Azospirillum,
Azotobacter,
Rhizobium,
Sesbania,
Blue Green Algae, and
Azolla.

6. 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

7. 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.

8. Mycorrhizae Refers to fungus associated with plant roots. 2 types:
Ectotrophic and
Endotrophic

9. 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

10. Azopirillum
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.

11. Azotobacter 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.

12. Rhizobia

13. Gram negative, motile, non-sporulating rods.
Forms root nodules in leguminous plants (Fabaceae) & fix atmospheric N2 (diazotrophy) in a symbiotic association

14. 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

15. Sesbania

16. Sesbania 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

17. 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)

18. Blue Green Algae or Cyanobacteria
Can carry out both photosynthesis as well as N2 fixation
Algal flakes are grown & then broadcasted.

19. Azolla

20. 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