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 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