A biofertilizer is a substance containing living which, when applied to seeds, plant surfaces, or soil, colonize the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary to the host plant.
Composition
Biofertilizers provide "eco-friendly" organic agro-inputs.
Rhizobium,
Azotobacter,
Azospirillum and
blue-green algae (BGA) are perhaps the species with the longest history of use as biofertilizers.
Rhizobium inoculant is used for leguminous crops.
Azotobacter can be used with crops like
wheat,
maize,
Mustard plant,
cotton,
potato, and other vegetable crops.
Azospirillum inoculations are recommended mainly for
sorghum,
millets,
maize,
sugarcane, and
wheat.
Blue-green algae belonging to the
cyanobacteria genera Nostoc,
Anabaena,
Tolypothrix, and
Aulosira fix atmospheric nitrogen and are used as inoculants for
paddy field grown in both upland and lowland conditions.
Anabaena, in association with the water fern
Azolla, can contribute nitrogen up to 60 kg/ha/season and can also enrich soils with organic matter.
Seaweeds are rich in various types of mineral elements (potassium, phosphorus, trace elements, etc.), hence they are extensively used as a form of manure replacement by people of coastal districts. Seaweed-fertilizer also helps in breaking down clays.
Fucus is used by Irish people as a biofertilizer on a large scale. In tropical countries, the bottom mud from dried-up ponds which contain abundant blue-green algae is regularly used as biofertilizer in fields.
Bacteria
Plant-Growth Promoting Microorganisms:
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Rhizobium: Symbiotic nitrogen fixation by Rhizobium with legumes contributes substantially to total nitrogen fixation. Rhizobium inoculation is a well-known agronomic practice to ensure adequate nitrogen.
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Bradyrhizobium (in particular Bradyrhizobium japonicum).
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Bacillus spp. (in particular B. amyloliquefaciens, B. mojavensis, B. thuringiensis, B. licheniformis, and B. subtilis).
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Priestia megaterium
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Azotobacter (A. chroococcum, A. vinelandii)
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Pseudomonas (P. fluorescens)
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Streptomyces
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Azospirilium
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Streptomyces grisoflavus
Fungi
Mycorrhiza fungi such as:
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Glomus spp.
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Rhizophagus irregularis
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Gigasporaceae. (in particular G. margarita)
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Trichoderma. (such as T. viride, T. harzianum, T. reesei, T. longibrachiatum, T. atroviride, T. koningii)
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Epichloë spp.
Archaea
Organic matter
-
Compost is commonly used as biofertilizers. It can be used directly on the soil or by using compost-derived products such as extracts or compost-tea made by fermenting compost mass. Vermicompost-based innoculants proposed by permaculture methods, Korean natural farming and JADAM
-
Manure
-
Lemnoideae
Seaweed and blue green algae:
Cyanobacteria:
Mechanisms
Biofertilizers work through multiple mechanisms. Plant-growth promoting rhizobacteria (PGPR) and
mycorrhizae are generally thought to increase the fixation of atmospheric nitrogen,
convert inorganic
phosphorus compounds into soluble forms, increase the
bioavailability of minerals in the soil,
and synthesize
plant hormone that promote growth, such as
and
gibberellin.
Another mechanism proposed is the AAC-
Deamination production of
Bacillus species, which prevents excessive increases in the synthesis of
ethylene under various stress conditions.
Benefits
Biofertilizers are cost-effective and ecofriendly in nature, and their continuous usage has been shown to enhance soil fertility.
Besides promoting growth by multiple mechanisms, biofertilizers produces substances suppressing
Plant disease, guarding plants from abiotic and biotic stresses and detoxification of belowground pollutants.
Extensive use of
Agrochemical in agricultural practices has been found to cause environmental disturbances and public health hazards affecting food security and sustainability in agriculture.
Biofertilizers offers an alternative solution for such agrochemicals, and show yield increase of up to about 10–40% by increasing protein contents, essential amino acids, and vitamins, and by nitrogen fixation.
Since a bio-fertilizer is technically living, it can associate with plant roots. Involved microorganisms could readily and safely convert complex organic material into simple compounds, so that they are easily taken up by the plants. Microorganism function is in long duration, causing improvement of the soil fertility. It maintains the natural habitat of the soil. It increases crop yield by 20-30%, replaces chemical nitrogen and phosphorus by 30%, and stimulates plant growth. It can also provide protection against drought and some soil-borne diseases. It has also been shown that to produce a larger quantity of crops, biofertilizers with the ability of nitrogen fixation and phosphorus solubilizing would lead to the greatest possible effect.
Future Research
Biofertilizers have been shown to have varying effects in different environments,
and even within the same environment. This is something that many scientists have been working on, however there is no perfect solution at this time. They however, have been shown to have the most profound effects in drier climates.
In the future, it is hoped that biofertilizers effects will be better controlled and regulated in all environments, as well as analysis targeted at specific species.
See also
