Classification of Biofertilizers

Biofertilizer contains living microorganisms which, when applied to soil, colonizes the rhizosphere or the interior of the plant and promotes growth by increasing the availability of primary nutrients to the host plant. 

Classification of Biofertilizers (Cover)

Types of Biofertilizers

The various types of biofertilizers which help the plant to grow at different levels of its growth are:

1. Nitrogen Fixing Biofertilizers

2. Phosphate Biofertilizers

    a. Phosphorous Solubilizing Biofertilizers

    b. Phosphorus Mobilizing Biofertilizers

3. Biofertilizers for Micro-nutrients

4. Plant Growth Promoting Rhizobacteria

5. Compost

1) Nitrogen Fixing Biofertilizers

i. Increase soil nitrogen level ii. Fixes the atmospheric nitrogen in the soil and make it available to the plants 

Examples: Azotobacter, Nostoc, Rhizobium, Azospirillum
a) Azobacter
i. Free living N-fixing bacterium
ii. Non-leguminous plants
b) Cyanobacteria
i. Nostoc/Blue green algae
ii. Free-living as well as symbiotic
iii. Fix atmospheric nitrogen to soil
c) Rhizobium
i. Symbiotic N-fixing bacterium
ii. Leguminous plants
d) Azospirillum
i. Associative symbiotic N-fixing bacteriumii. Graminaceous plants

2) Phosphate Biofertilizers

a. Phosphorous Solubilizing Biofertilizersb. Phosphorus Mobilizing Biofertilizers

a) Phosphorus Solubilizing Biofertilizers

i. Solubilize the insoluble phosphate from organic and inorganic phosphate sources

ii. Releases insoluble phosphorus in soil and fix in clay minerals

iii. Secrete organic acids and lower the pH to dissolve bound phosphates in soil

Examples: Species of Bacillus, Pseudomonas, Penicillium, Aspergillus

b) Phosphorus Mobilising Biofertilizers

Transfer phosphorus from the soil to the root cortex

Examples: Arbuscular Mycorrhiza (AM fungi)

i.Fungus penetrates the cortical cells of the roots

ii. Increase surface area of roots

iii.Displace of absorption equilibrium of phosphate ions which increases the transfer of P ions

iv. Stimulate metabolic processes

v. Arbuscles absorb these nutrients into the root system

3) Biofertilizers for Micro-nutrients

i. Bacterial species are Silicate and Zinc solubilizers

ii. Degrade silicates and aluminium silicates in soil

iii. Help in silicate weathering

Example: Bacillus sp.

4) Plant Growth Promoting Rhizobacteria (PGPRs)

i. Act as both Biofertilizer and Biopesticides

ii. Promote growth by:

    a) Improved Nutrient Availability (Biofertilizers)

    b) Suppression of Plant Disease (Bioprotectants)

    c) Phytohormones Production (Biostimulants)

Roles of PGPR

Examples: Pseudomonas sp., Bacillus sp.

PGPR Action

5) Compost Biofertilizers

i. Utilize animal dung to enrich soil with microorganisms

ii. Eco-friendly organic fertilizer

iii. Consists of nitrogen, phosphate solubilizing bacteria and various decomposing fungi

iv. Microorganisms breaks down organic matter (dead plants, farm yard waste, cattle waste etc.)

Examples: Cellulolytic fungi, Azotobacter

Compost Biofertilizers [Uses (Left) and mode of action(Right)]

Liquid Biofertilizers

i. Liquid biofertilizers are suspensions having agriculturally useful microorganisms, which fix atmospheric nitrogen and solubilize insoluble phosphates and make it available for the plant

ii. Reduces the use of chemical fertilizer by 15-40%

iii. Long shelf life

iv. More temperature tolerant and contamination free

v. Easy to produce and apply

vi. Help to produce organic crops so as to compete in the global market

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Related Articles on Biofertilizers: 

1) Introduction to Biofertilizers

2) Status of Biofertilizers in Pakistan: Their Application Methods and Advantages

3) Phosphate Biofertilizers - Enhancing Soil Fertility

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Post by: Saman Riaz (M.Phil Scholar-CEMB)