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Biofertilizer notes

Submitted by Mousumi Sepai, Last Modified on 2019-12-24

Biofertilizer definition

Biofertilizer is a substance which contains living microorganisms 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 add nutrients through the natural process of fixing atmospheric nitrogen, solubilizing phosphorus, and stimulating plant growth through the synthesis of growth promoting substances. They can be grouped in different ways based on their nature and function.

Different types of biofertilizers

  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 molecules 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/na/year is fixed by different legume crops by the microbial activities of Rhizobium.

  2. Azotobacter:- It is an important and well known free living nitrogen fixing aerobic bacterium. It is used as a Biofertilizer for all non leguminous plants especially rice, cotton, vegetables etc. Azabacter cells are not present on the rhizoplane but are abundant in the rhizosphere region. The lack of organic matter in the soil is a limiting factor for the proliferation of Azotobacter 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/na in the rhizosphere in non-leguminous plants such cereals, millets, oil seeds, 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 algae Anabaena Azollae. 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. 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):- Phosphate solubilizing microorganisms(PSM) are beneficial microorganisms capable of solubilizing inorganic phosphorus from insoluble compounds.

  7. Fungi:- An arbuscular mycorrhiza is a type of mycorrhiza in which the fungus penetrates the cortical cells of the roots of a vascular plant.

  8. Silicate solubilizing bacteria:- Microorganisms are capable of degrading silicates and aluminium 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 bacterial to crops are referred to as plant growth promoting rhizobacteria.


Role of biofertilizers in soil fertility and agriculture

Biofertilizers are known to play a number of vital roles in soil fertility, crop productivity and production in agriculture as they are eco friendly and can not at any cost replace chemical fertilizers that are indispensable for getting maximum crop yields some of the important functions or roles of biofertilizers in agriculture are.

  1. They supplement chemical fertilizers for meeting the integrated nutrient demand of the crop.

  2. They can add 20-200 kg N/na year (eg. Rhizobium sp. 50-100 kg N/na year, Azospirillum Azotobacter 20-40kg N/na/yr. Azolla 40-80 kg N/na, BGA: 20-30 kg N/na) under optimum soil conditions and thereby increases 15-25 percent of total crop yield.

  3. They can at best minimize the use of chemical fertilizers no exceeding 40-50 kg N/na under ideal agronomic and pest free conditions.

  4. Application of biofertilizers results in increased mineral and water uptake, root development, vegetative growth and nitrogen fixation.

  5. Some biofertilizers stimulate production of growth promoting substance like Vitamin-B complex, Indole acetic acid(IAA) and Gibberellic acids etc.

  6. Phosphate mobilizing or phosphorus solubilizing biofertilizers? micro organisms(bacteria, fungi). Converts insoluble soil phosphate into soluble forms by secreting several organic acids and under optimum conditions they can solubilize/mobilize about 30-50 kg P205/na due to which crop yield may increase by 10%-20%.

  7. Mycorrhiza or VA-mycorrhiza when used as biofertilizer enhance uptake of P, Zn, S and water, leading to uniform crop growth and increased yield and also enhance resistance to root diseases and improve hardiness of transplant stock.

  8. They liberate growth promoting substances and vitamins and help to maintain soil-fertility.

  9. They act as antagonists and suppress the incidence of soil borne plant pathogens and thus, help in the bio-control of diseases.

  10. They improve physical properties of soil, soil tilth and soil health in general.

  11. The improved soil fertility and soil productivity.

  12. BGA play a vital role in the nitrogen economy of rice fields in tropical regions.

  13. Plays an important role in the recycling of plant nutrients.

  14. They are cheaper, pollution free and renewable energy sources.

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