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
• 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:
• 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.
Mycorrhizae
• 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
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.
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.
Rhizobia
• 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
Sesbania
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
• 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
• or Cyanobacteria
• Can carry out both photosynthesis as well
as N2 fixation
• Algal flakes are grown & then
broadcasted.
Azolla
• 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 bluegreen 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