What are Biofertilizers ?
Author: Sandeep Kumar Bangarwa

  • 'Biofertilizer' is a substance which contains living microorganism which, when applied to seed, plant surfaces, or soil, colonizes the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant.Biofertilizers are not fertilizers.
  • Fertilizers directly increase soil fertility by adding nutrients. Biofertilizers add nutrients through the natural processes of fixing atmospheric nitrogen, solubilizing Phosphorus, and stimulating plant growth through the synthesis of growth promoting substances.
  • Microorganism induce many biochemical transformation in soil. These include mineralisation of organically bound forms of nutrients, exchange reactions, fixation of atmospheric nitrogen and various other changes leading to better availability of nutrients already present in the soil.
  • The group of microorganism responsible for nitrogen fixation, phosphate solubilisation and compost decomposition are being put to beneficial use in the form of Biofertilizers.
  • Biological nitrogen fixation contributes maximum ( 67.5%) towards enriching earth surface with nitrogen.
  • Microorganism capable of assimilating nitrogen are marked with “ nif” genes. They synthesise nitrogenase enzyme responsible for converting otherwise inert N2 to plant usable NH3. Such common useful organism are Rhizobium, Azatobacter, Azospirillium and Blue Green Algae ( BGA).
  • There are some microorganisms capable of solubilising insoluble soil phosphours while some collect available phosphorous from remote places out of reach of plant root hairs by sending elongated filaments. E.g. Vesicular Arbuscular Mycorrhiza.
  • Few of the heterotropic organisms decompose cellulose rapidly. Such beneficial organisms are domesticated in suitable carriers which on application to soil augment crop growth and yield. These carrier based microorganisms are called Biofertilizers or appropriately called bioinoculants or microbial inoculants or microbial fertilizers.
  • Biofertilizers can be grouped in different ways based on their nature and function.
(A) Nitrogen fixing Biofertilizers

1. Free-living - Azotobacter, Clostridium, Anabaena, Nostoc

2. Symbiotic - Rhizobium, Frankia, Anabaena azollae

3. Associative Symbiotic – Azospirillum

(B) Phosphorous solubilizing Biofertilizers

1. Bacteria - Bacillus megaterium var. phosphaticum, Bacillus circulans, Pseudomonas striata

2. Fungi - Penicillium sp, Aspergillus awamori

(C) Phosphorous mobilizing Biofertilizers

1. Arbuscular mycorrhiza - Glomus sp.,Gigaspora sp.,Acaulospora sp., Scutellospora sp. & Sclerocystis sp.

2. Ectomycorrhiza - Laccaria sp., Pisolithus sp., Boletus sp., Amanita sp.

3. Orchid mycorrhiza - Rhizoctonia solani

(D) Biofertilizers for micronutrients

1. Silicate and Zinc solubilizers - Bacillus sp.

(E) Plant growth promoting rhizobacteria

1. Pseudomonas - Pseudomonas fluorescens

  • The common microorganisms which have shown positive increase in crop yield and can possibly be used as Biofertilizers are as below: -
(A) Nitrogen

1. Symbiotic organisms

(a) Rhizobium (Symbiosis with Legumes)

  • Pulse Legumes:- Chickpea, Pea, Lentil, Moong, Urad Bean, Pigeon Pea
  • Oil Legumes:- Groundnut, Soyabean
  • Fodder Legume: -Berseem, Lucern
(b) Azolla (Water Fern) Azolla Ap. + BGA Symbiosis :- Rice

2. Associative Symbiotic organisms

(a) Azospirillum

  • Sorghum, Perl Millet, Rice, Wheat, Finger Millet, Maize, Kodo Kutaki, Tomato, Chilli
3. Non-Symbiotic organisms

(a) Azatobacter (Heterotrophs)

  • Cereals: Wheat, Rice, Maize, Sorghum, Sugarcane
  • Vegetables: Onion, Brinjal, Tomato, Cabage
  • Flowers: Chrysanthemum, Marygold
(b) Blue Green Algai (Photoautotrophs) :- Rice

(B) Phosphorous

1. "P" solubilizers and mineralizers

(a) ) Fungi - Aspergillus, Penicillum

  • For All Crops
(b) Bacteria - Bacillus Psudomonas

  • For All Crops
2. "P" Absorbers (Root Fungus Symbiosis)

(a) Versicular Arbuscular Mycorrhiza (VAM)

  • For All Crops
(b) Ectomycorrhizae

  • For All Crops
(c) Endomycorrizae Clomus :- Linseed, Maize, Wheat, Soyabean

( Different types of Bio-fertilizers )

1. Rhizobium

  • This belongs to bacterial group and the classical example is symbiotic nitrogen fixation.
  • The bacteria infect the legume root and form root nodules within which they reduce molecular nitrogen to ammonia which is reality utilized by the plant to produce valuable proteins, vitamins and other nitrogen containing compounds.
  • The site of symbiosis is within the root nodules.
  • It has been estimated that 40-250 kg N / ha / year is fixed by different legume crops by the microbial activities of Rhizobium.
2. Azotobacter

  • It is the important and well known free living nitrogen fixing aerobic bacterium .
  • It is used as a Bio-Fertilizer for all non leguminous plants especially rice, cotton, vegetables etc.
  • Azotobacter cells are not present on the rhizosplane but are abundant in the rhizosphere region.
  • The lack of organic matter in the soil is a limiting factor for the proliferation of Azotobaceter in the soil.
3. Azospirillum

  • It belongs to bacteria and is known to fix the considerable quantity of nitrogen in the range of 20- 40 kg N/ha in the rhizosphere in non- leguminous plants such as cereals, millets, Oilseeds, cotton etc.
4. Cyanobacteria

  • A group of one celled to many celled aquatic organisms. Also known as blue-green algae.
5. Azolla

  • Azolla is a free floating water fern that floats in water and fixes atmospheric nitrogen in association with nitrogen fixing blue green alga Anabaenaazollae.
  • Azolla fronds consist of sporophyte with a floating rhizome and small overlapping bi-lobed leaves and roots.
  • Azolla is considered to be a potential biofertilizer in terms of nitrogen contribution to rice.
  • Long before its cultivation as a green manure, Azolla has been used as a fodder for domesticated animals such as pigs and ducks.
  • In recent days, Azolla is very much used as a sustainable feed substitute for livestock especially dairy cattle, poultry, piggery and fish
6. Phosphate solubilizing microorganisms (PSM)

7. AM fungi

  • An arbuscular mycorrhiza (AM Fungi) is a type of mycorrhiza in which the fungus penetrates the cortical cells of the roots of a vascular plant.
8. Silicate solubilizing bacteria (SSB)

  • Microorganisms are capable of degrading silicates and aluminum silicates .
  • During the metabolism of microbes several organic acids are produced and these have a dual role in silicate weathering.
9. Plant Growth Promoting Rhizobacteria (PGPR)

The group of bacteria that colonize roots or rhizosphere soil and beneficial to crops are referred to as plant growth promoting rhizobacteria (PGPR).

1. Rao, D.L.N. (2014) Soil Biodiversity - Biofertilizers Research Progress (2012 -14). All India Network Project on Soil Biodiversity- Biofertilizers, IISS, Bhopal, pp 81.
2. Rao D.L.N. (2014) Recent Advances in Biological Nitrogen Fixation in Agricultural Systems. Proc. Ind. Natnl. Sci. Acad80 Spl. Sec: 359-378.
3. Aggani, S.L.(2013) Development of Bio-Fertilizers and its Future Perspective. Sch. Acad. J. Pharm.,2013; 2(4):327-332.
4. Wikipedia

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