This document discusses various types of biofertilizers, including nitrogen-fixing bacteria like Azospirillum, Azotobacter, and Rhizobia that form symbiotic relationships with plants, fixing atmospheric nitrogen. It also mentions phosphate-solubilizing microbes that make phosphorus more available to plants, mycorrhizal fungi that help with nutrient and water absorption, and algae like blue-green algae and Azolla that can fix nitrogen through associations with cyanobacteria. The document provides details on the organisms used in biofertilizers and their benefits for enriching soils and supporting plant growth.

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. • 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