http://vjahnavi57.blogspot.in/2010/11/bio-fertilizers.html
life science
Sunday, November 21, 2010
BIO FERTILIZERS.
BACTERIAL BIOFERTILIZERS
LUIS E. FUENTES-RAMIREZ1 and JESUS CABALLERO-MELLADO2,
1 Laboratorio de Microbiología de Suelos, Centro de Investigaciones Microbiológicas, Instituto de Ciencias; Universidad Autónoma de Puebla. Apdo. Postal No. 1622, Puebla, Puebla, México;
2 Programa de Ecología Molecular y Microbiana, Centro de Investigación sobre Fijación de Nitrógeno; Universidad Nacional Autónoma de México, Apdo. Postal No. 565-A, Cuernavaca, Morelos, México.
ABSTRACT:
Many bacteria and fungi can enhance plant growth. The present review is limited to plant growth promoting rhizobacteria (PGPR). However, it includes endophytic bacteria that show plant growth enhancing activity as well. Also the best studied bacterial mechanisms of plant growth promotion are discussed, with a special emphasis on biological nitrogen fixation and synthesis of phytohormones, including less understood mechanisms like inhibition of plant ethylene synthesis, degradation of organic-P compounds, phenazine-related mineral solubilization, and synthesis of lumichrome. In addition, examples of PGPR genes that show activation in the interaction with plants, and beneficial events resulting from plant-bacterial interactions like stress relief and enhancement of other ecological associations are presented. Plant growth promoting activity and more precisely, crop yield enhancement are the final effects of the different mechanisms that PGPR possess and are the applicative goal of the agricultural microbiology research. Despite the undoubted economic and ecological benefits of utilizing some PGPR species as biofertilizers, the application of such a species must be very carefully assessed because of their importance as opportunistic pathogens in nosocomial infections and in patients with other diseases. On this basis, PGPR species must be selected for producing safe biofertilizers. Strain selection, as also the number of the bacterial cells, and characteristics of the bacterial cultures used in the production of biofertilizers, as well as, results of inoculation of different crops and cultivars with Azospirillum under field conditions are also included in the discussion. Key words: bacterial inoculation; endophytic bacteria; nitrogen fixation; phytohormones; rhizosphere bacteria; plant growth promoting rhizobacteria. 143 © 2005 Springer. Printed in the Netherlands. Z. A. Siddiqui (ed.), PGPR: Biocontrol and Biofertilization, 143–172. 144 Fuentes-Ramirez and Caballero-Mellado 1 INTRODUCTION Plant growth promoting rhizobacteria (PGPR) have been studied for long. It has been suggested in the last few years that endophytic N2-fixing bacteria may be more important than rhizospheric bacteria in promoting plant growth because they escape competition with rhizosphere microorganisms and achieve close contact with the plant tissues (Assmus et al., 1995; Döbereiner, 1992). The well known genera of PGPR are Azospirillum, Azotobacter, Bacillus, Burkholderia, Enterobacter, Klebsiella, and Pseudomonas, but some of these genera include endophytic species as well. The best-characterized endophytic bacteria include Azoarcus spp, Gluconacetobacter diazotrophicus, and Herbaspirillum seropedicae. Novel Burkholderia species, for instance, B. unamae (Caballero-Mellado et al., 2004) and B. tropica (Reis et al., 2004) have the potential for promoting plant growth (Caballero-Mellado et al., 2003) and are found in rhizospheric and endophytic association with different agricultural crops. Bacterial mechanisms of plant growth promotion include biological nitrogen fixation (BNF), synthesis of phytohormones, environmental stress relief, synergism with other bacteria-plant interactions, inhibition of plant ethylene synthesis, as well as increasing availability of nutrients like phosphorus, iron and minor elements, and growth enhancement by volatile compounds. However, the expression of such bacterial activities under laboratory conditions does not guarantee in association with a host plant. This is especially true of nitrogenfixation as abundantly expressed in culture media by many bacterial species. The mechanisms of plant growth promotion have been analyzed in different organisms, especially in Azospirillum spp. and in few other PGPR (Vande Broek et al., 2000; Lucy et al., 2004). In this review, Azospirillum as a model for studying mechanisms of plant growth promotion will only be covered briefly but some other models and new mechanisms will be presented in more depth. Many definitions and interpretations of the term biofertilizer exist (Vessey, 2003). In this chapter, a biofertilizer is a product that contains living microorganisms, which exert direct or indirect beneficial effects on plant growth and crop yield through different mechanisms. The term biofertilizer as used here could include products containing bacteria to control plant pathogens, but these are frequently referred to as biopesticides (Siddiqui and Mahmood, 1999; Burdman et al., 2000;VESSEY,2003
life science
Sunday, November 21, 2010
BIO FERTILIZERS.
Man began to cultivate the land in an organized way for food but the same land could not support the cultivation endlessly and this led him to think about the way and means of improving the fertility of soil.
In early days of agriculture, man increased the soil fertility with organic manure derived from crop and cattle residues then man made fertilizers containing nitrogen(N), Phosphorous(P), Potassium(k) which were called as ‘chemical fertilizers’.
These chemical fertilizers no doubt increase the product but also produced many harmful effects. Therefore, efforts have been made towards the use of bio fertilizers.
NEED FOR USE OF BIO FERTILIZERS:
The need for the use of bio fertilizers has arisen for 3 reasons:
1) Because increase in the use of fertilizers lead to increase crop productivity.
2) Because increase use of chemical fertilizers leads to damage in soil texture and other environmental problems are caused.
3) Chemical fertilizers are manufactured from petroleum, oil, coal.
The increase cost of these fossil fuels results in ever increasing cost of chemical fertilizers. Therefore, the use of bio fertilizers is both economical and environment friendly.
Biologically fixed nitrogen can supply and adequate amount of nitrogen to plants and other nutrients to some extent. It is non-hazardous way of fertilizers of soil.
BIOFERTILIZERS:
The term bio fertilizers denotes all nutrients input for plant growth which are of biological origin.
Bio fertilizers can be defined as preparations containing live or latent cells of efficient strains of nitrogen fixing and phosphate solubilizing organisms.
Soil or composting areas with the objective of increasing the number of such micro organisms and accelerate certain microbial processes to argument the extent of availability of nutrients in a form which can be easily assimilated by plants.
POTENTIAL ORGANISMS FOR BIO FERTILIZERS:
A good number of micro organisms of bacteria, algae, fungi are being identified and exploited as potential source of bio fertilizers.
BACTERIAL BIO FERTILIZERS:
Bacterial bio fertilizers comprises of:
Ø Nitrogen fixing bacterial organisms
Ø Phosphate solubilizing organisms
NITROGEN FIXING BACTERIAL BIO FERTILIZERS:
Many free living and symbiotic bacteria fix atmospheric nitrogen.
Increase of such bacteria in soil may increase the gross yield of nitrogen.
The 2 methods are:
Ø Bacterization
Ø Green manuring.
Bacterization is a technique of seed dressing with bacteria.
Eg:azotobacter ,bacillus, rhizobium.
It has been known that bacteria can successfully be established in root region of plants which in turn improve the growth of host.
Eg;Bacterial fertilizers named azotobacterium containing cells of azotobacter and chrococcum.
Phospho bacterium containing cells of Bacillus megatherium and Phosphoticum can be used as fertilizers which increases upto 10-20%
In rhizosphere , bacteria secrete growth substances and antibiotic secondary metabolites which contribute to seed germination and plant growth.
RHIZOBIUM:
Rhizobium exist in symbiotic relationship with legumes.They fiix atmospheric nitrogen and thus not only increase the production of the inoculated crops but also leave a sufficient amt of nitrogen in the soil which benefits the subsequent crop.
Seven groups of rhizobium have been recognized for inoculating legumes in India.
v Inoculated with theeRhizobium leguminosarum
v Rhizobium japonicum
v Rhizobium trifoli
v Rhizobium melilothi
v Rhizobium phaseoli
v Rhizobium lupinci
v Rhizobium species
The nitrogen fixing ability of legumes inoculated with these rhizobium ranges from 50kg to 150kg/hectare.Hence to increase thi ability to fix atmospheric nitrogen following efforts are being made:
1) Efficient rhizobia for different crops and locations which are tolerant to various stresses like drought, temperature, increased or decreased PH are being isolated, maintained and used.
2) Hop+ gene is being used which helps in recycling of hydrogen produced during nitrogen fixation.
3)Strains deficient in nitrate reductase have improved nitrogen fixation ability.
RHIZOBIUM.
AZOTOBACTER:
Azotobacter Vinelandii is a free-living bacterium that can fix atmosferic nitrogen into the soil, being a great source to obtain a natural biofertilizer that can be used in the cultivation of most crops.
It is a great source of nitrogen to meet the needs of crops because also has the capabilities to cause a rejuvenation of soil microbiology to tap out the biological fixation of nitrogen.
Azotobacter is Gram negative bacteria, polymorphic i.e. they are of different sizes and shapes. Their size ranges from 2-10x1-2.5 m ., young cell possess peritrichous flegella and are used as locomotive organs. Old population of bacteria includes encapsulated forms and have enhanced resistant to heat, desication and adverse conditions. The cyst germinates under favourable conditions to give vegetative cells. They also produce polysachharides. Azotobacter spp.,are sensitive to acidic pH, high salts, and temperature above 350C.
There are four important species of Azotobacter viz. A.Chroococcum, A.agilis, A.paspali and A.vinelandii of which A.chroococcum is most commonly found in our soils.
Nitrogen fixation by Azotobacter:
The species of Azotobacter are known to fix on an average 10 mg.of N/g of sugar in pure culture on a nitrogen free medium. A maximum of 30 mg. N fixed per gram of sugar was reported by lopatina. However, Azotobacter is a poor competitor for nutrients in soil. Most efficient strains of Azotobacter would need to oxidise about 1000 kg of organic matter for fixing 30 kg of N/ha. This does not sound realistic for our soils which have very low active carbon status. Besides, soil is inhabitated by a large variety of otherr microbes, all of which compete for the active carbon.
BENEFITS:
· It improves seed germination and plant growth
· Azotobacter are tolerant to high salts.
· It can benefit crops by Nitrogen fixation, growth promoting substances, fungi static substances.
· Azotobacter is heaviest breathing organism and requires a large amount of organic carbon for its growth.
· It is poor competitor for nutrients in soil and hence its growth promoting substances, fungistatic substances.
· It thrives even in alkaline soils.
· Azotobacter is less effective in soils with poor organic matter.
AZOTOBACTER
PHOSPHATE SOLUBILIZING BACTERIA:
In the soil phosphate is present in the combined forms with Ca, Fe, Al etc and are insoluble in water.They are converted into soluble phosphates by the activities of microbes which are called phosphate solubilizers.eg:Bacillus megatherium,Psedomonas, Psedomonas putida.
Some fungi like aspergillus, pencillium are also phosphate solubilizers but have not been used in commericial preparation of bio fertilizers.
The phosphate solubilizers secrete many organic acids ike HCOOH, CH3COOH,Succinic acid, Propionic acid etc in the soil.These acids react with rock phosphate to make them soluble in water.Thus, they convert inorganic phosphate into soluble phosphate which can be utilized by crop plants.
These bio fertilizers reduce the use of phosphate fertilizers in agriculture.
ALGAL BIOFERTILIZERS:
This comprises mainly of blue green algae
The importance of blue green algae (cyanobacteria) os bio fertilizers were recognized as early as 1939.
Blue green algae constitute an important group of micro organism capable of fixing atmospheric nitrogen.They comprises unicellular,colonial and filamentous forms.
Most of the nitrogen fixing blur green algae belongs to the genera Anabene, Nostoc, Cytoneme, Plectonema etc.In general N2 fixation is associated with forms possessing heterocysts.
The process of application of blue green algal culture in fields as bio fertilizers is known as ALGALIZATION.
In water logged conditions., blur green algae such as Anabene, nostoc multiply, fix atmospheric nitrogen and release it into the surroundings in the form of aminoacids, proteins and other growth promoting substances.
The benefit from algalizatio is about 25-30kg/hectare/cropping season
SPIROGYRA:
It is a non living nitrogen fixing algae. Its inoculations severs as organic biomass for the growing rice plants.
Furthur, the mucilaginous sheath of the filaments of spirogyra is an abode of many micro organisms some of which may fix nitrogen.
ANABENA-AZOLLA:
Anabena is a blue green algae which exist in a symbiotic association wit azolla a pteridophytic plant
Both the hast and the symbiotic Anabena which reside on the dosal lobe at azolla leaves are capable of photosynthesis but the nitrogen requirement of the host are fulfilled by the symbiont through nitrogen fixation.
An intreasting feature of Azolla-Anabena association is that the symbiosis is maintained during the saprophytic and gametophytic cycles
Azolla mat is harvested and dried to use as green manure
There are 2 methods of application in the field:
a)Incorporation of Azolla in soil prior to rice plantation./
b)Transplantation of the rice followed by the water drawing and incorporation of Azolla.
Azolla is capable of producing about 900kg of nitrogen/hectare/year.
The daily nitrogen rate is as high as7 kg nitrogen/hectare
ANEBENA
LIMITATIONS:
There are certain limitations in using Azolla as bio fertilizers.
a)Azolla as a green manure crop is labour intensive
c) Otimum temperature is required for Azolla multiplication.
MYCORRHIZAE:
It is a symbiotic association of fungi with plant roots.
Fungus absorbs nutrients from the soil and releases it into the host cell and in turn host supplies the fungus with food requirements.
Mycorrhizae helps in growth of plants by inhibiting the growth of pathogenic bacteria present in the soil.
There are 2 types of mycorrhizae
1)ecto mycorrhiza
2)endo mycorrhiza.
ECTOMYCORRHIZA:
Ectomycorrhizas, or EcM, are typically formed between the roots of around 10% of plant families, mostly woody plants including the birch, dipterocarp, eucalyptus, oak,pine, and rose families and fungi belonging to theBasidiomycota, Ascomycota, and Zygomycota. Ectomycorrhizas consist of a hyphal sheath, or mantle, covering the root tip and a hartig net of hyphae surrounding the plant cells within the root cortex. In some cases the hyphae may also penetrate the plant cells, in which case the mycorrhiza is called an ectendomycorrhiza. Outside the root, the fungal mycelium forms an extensive network within the soil and leaf litter. Nutrients can be shown to move between different plants through the fungal network. Carbon has been shown to move frompaper birch trees into Douglas-fir trees thereby promotingsuccession in ecosystems. The ectomycorrhizal fungusLaccaria bicolor has been found to lure and kill springtailsto obtain nitrogen, some of which may then be transferred to the mycorrhizal host plant.
The first genomic sequence for a representative of symbiotic fungi, the ectomycorrhizal basidiomyceteLaccaria bicolor, has been published. An expansion of several multigene families occurred in this fungus, suggesting that adaptation to symbiosis proceeded by gene duplication. Within lineage-specific genes those coding for symbiosis-regulated secreted proteins showed an up-regulated expression in ectomycorrhizal root tips suggesting a role in the partner communication. Laccaria bicolor is lacking enzymes involved in the degradation of plant cell wall components (cellulose, hemicellulose, pectins and pectates), preventing the symbiont from degradind the host cells during root colonization.
ENDO MYCORRHIZA:
Endomycorrhiza are variable and have been further classified as arbuscular, ericoid, arbutoid, monotropoid, and orchid mycorrhizae. Arbuscular mycorrhizas, or AM (formerly known as vesicular-arbuscular mycorrhizas, or VAM), are mycorrhizas whose hyphae enter into the plant cells, producing structures that are either balloon-like (vesicles) or dichotomously-branching invaginations (arbuscules). The fungal hyphae do not in fact penetrate the protoplast (i.e. the interior of the cell), but invaginate the cell membrane. The structure of the arbuscules greatly increases the contact surface area between the hypha and the cell cytoplasm to facilitate the transfer of nutrients between them.
Arbuscular mycorrhizae are formed only by fungi in thedivision Glomeromycota. Fossil evidence and DNA sequence analysissuggest that this mutualism appeared400-460 million years ago, when the first plants were colonizing land. Arbuscular mycorrhizas are found in 85% of all plant families, and occur in many crop species. The hyphae of arbuscular mycorrhizal fungi produce the glycoprotein glomalin, which may be one of the major stores of carbon in the soil. Arbuscular mycorrhizal fungi have (possibly) been asexual for many millions of years and, unusually, individuals can contain many genetically different nuclei (a phenomenon called heterokaryosis). Many plants in the order Ericales form ericoid mycorrhizas, while some members of the Ericales form arbutoid and monotropoid mycorrhizas. All orchids are mycoheterotrophic at some stage during their lifecycle and form orchid mycorrhiza with a range of basidiomycete fungi.
Mycorrhizal innoculations stimulate rooting and growth and there by transplant survival of cutting and seedling which is essential for the successful reclamation and forestation programs.
Due to this beneficial attributes the mycorrhizae are widely used as bio fertilizer for improving the growth of agriculture and horticulture plants
Thanks :
http://vjahnavi57.blogspot.in/2010/11/bio-fertilizers.html
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.719.2177&rep=rep1&type=pdf
life science
Sunday, November 21, 2010
BIO FERTILIZERS.
BACTERIAL BIOFERTILIZERS
LUIS E. FUENTES-RAMIREZ1 and JESUS CABALLERO-MELLADO2,
1 Laboratorio de Microbiología de Suelos, Centro de Investigaciones Microbiológicas, Instituto de Ciencias; Universidad Autónoma de Puebla. Apdo. Postal No. 1622, Puebla, Puebla, México;
2 Programa de Ecología Molecular y Microbiana, Centro de Investigación sobre Fijación de Nitrógeno; Universidad Nacional Autónoma de México, Apdo. Postal No. 565-A, Cuernavaca, Morelos, México.
ABSTRACT:
Many bacteria and fungi can enhance plant growth. The present review is limited to plant growth promoting rhizobacteria (PGPR). However, it includes endophytic bacteria that show plant growth enhancing activity as well. Also the best studied bacterial mechanisms of plant growth promotion are discussed, with a special emphasis on biological nitrogen fixation and synthesis of phytohormones, including less understood mechanisms like inhibition of plant ethylene synthesis, degradation of organic-P compounds, phenazine-related mineral solubilization, and synthesis of lumichrome. In addition, examples of PGPR genes that show activation in the interaction with plants, and beneficial events resulting from plant-bacterial interactions like stress relief and enhancement of other ecological associations are presented. Plant growth promoting activity and more precisely, crop yield enhancement are the final effects of the different mechanisms that PGPR possess and are the applicative goal of the agricultural microbiology research. Despite the undoubted economic and ecological benefits of utilizing some PGPR species as biofertilizers, the application of such a species must be very carefully assessed because of their importance as opportunistic pathogens in nosocomial infections and in patients with other diseases. On this basis, PGPR species must be selected for producing safe biofertilizers. Strain selection, as also the number of the bacterial cells, and characteristics of the bacterial cultures used in the production of biofertilizers, as well as, results of inoculation of different crops and cultivars with Azospirillum under field conditions are also included in the discussion. Key words: bacterial inoculation; endophytic bacteria; nitrogen fixation; phytohormones; rhizosphere bacteria; plant growth promoting rhizobacteria. 143 © 2005 Springer. Printed in the Netherlands. Z. A. Siddiqui (ed.), PGPR: Biocontrol and Biofertilization, 143–172. 144 Fuentes-Ramirez and Caballero-Mellado 1 INTRODUCTION Plant growth promoting rhizobacteria (PGPR) have been studied for long. It has been suggested in the last few years that endophytic N2-fixing bacteria may be more important than rhizospheric bacteria in promoting plant growth because they escape competition with rhizosphere microorganisms and achieve close contact with the plant tissues (Assmus et al., 1995; Döbereiner, 1992). The well known genera of PGPR are Azospirillum, Azotobacter, Bacillus, Burkholderia, Enterobacter, Klebsiella, and Pseudomonas, but some of these genera include endophytic species as well. The best-characterized endophytic bacteria include Azoarcus spp, Gluconacetobacter diazotrophicus, and Herbaspirillum seropedicae. Novel Burkholderia species, for instance, B. unamae (Caballero-Mellado et al., 2004) and B. tropica (Reis et al., 2004) have the potential for promoting plant growth (Caballero-Mellado et al., 2003) and are found in rhizospheric and endophytic association with different agricultural crops. Bacterial mechanisms of plant growth promotion include biological nitrogen fixation (BNF), synthesis of phytohormones, environmental stress relief, synergism with other bacteria-plant interactions, inhibition of plant ethylene synthesis, as well as increasing availability of nutrients like phosphorus, iron and minor elements, and growth enhancement by volatile compounds. However, the expression of such bacterial activities under laboratory conditions does not guarantee in association with a host plant. This is especially true of nitrogenfixation as abundantly expressed in culture media by many bacterial species. The mechanisms of plant growth promotion have been analyzed in different organisms, especially in Azospirillum spp. and in few other PGPR (Vande Broek et al., 2000; Lucy et al., 2004). In this review, Azospirillum as a model for studying mechanisms of plant growth promotion will only be covered briefly but some other models and new mechanisms will be presented in more depth. Many definitions and interpretations of the term biofertilizer exist (Vessey, 2003). In this chapter, a biofertilizer is a product that contains living microorganisms, which exert direct or indirect beneficial effects on plant growth and crop yield through different mechanisms. The term biofertilizer as used here could include products containing bacteria to control plant pathogens, but these are frequently referred to as biopesticides (Siddiqui and Mahmood, 1999; Burdman et al., 2000;VESSEY,2003
life science
Sunday, November 21, 2010
BIO FERTILIZERS.
Man began to cultivate the land in an organized way for food but the same land could not support the cultivation endlessly and this led him to think about the way and means of improving the fertility of soil.
In early days of agriculture, man increased the soil fertility with organic manure derived from crop and cattle residues then man made fertilizers containing nitrogen(N), Phosphorous(P), Potassium(k) which were called as ‘chemical fertilizers’.
These chemical fertilizers no doubt increase the product but also produced many harmful effects. Therefore, efforts have been made towards the use of bio fertilizers.
NEED FOR USE OF BIO FERTILIZERS:
The need for the use of bio fertilizers has arisen for 3 reasons:
1) Because increase in the use of fertilizers lead to increase crop productivity.
2) Because increase use of chemical fertilizers leads to damage in soil texture and other environmental problems are caused.
3) Chemical fertilizers are manufactured from petroleum, oil, coal.
The increase cost of these fossil fuels results in ever increasing cost of chemical fertilizers. Therefore, the use of bio fertilizers is both economical and environment friendly.
Biologically fixed nitrogen can supply and adequate amount of nitrogen to plants and other nutrients to some extent. It is non-hazardous way of fertilizers of soil.
BIOFERTILIZERS:
The term bio fertilizers denotes all nutrients input for plant growth which are of biological origin.
Bio fertilizers can be defined as preparations containing live or latent cells of efficient strains of nitrogen fixing and phosphate solubilizing organisms.
Soil or composting areas with the objective of increasing the number of such micro organisms and accelerate certain microbial processes to argument the extent of availability of nutrients in a form which can be easily assimilated by plants.
POTENTIAL ORGANISMS FOR BIO FERTILIZERS:
A good number of micro organisms of bacteria, algae, fungi are being identified and exploited as potential source of bio fertilizers.
BACTERIAL BIO FERTILIZERS:
Bacterial bio fertilizers comprises of:
Ø Nitrogen fixing bacterial organisms
Ø Phosphate solubilizing organisms
NITROGEN FIXING BACTERIAL BIO FERTILIZERS:
Many free living and symbiotic bacteria fix atmospheric nitrogen.
Increase of such bacteria in soil may increase the gross yield of nitrogen.
The 2 methods are:
Ø Bacterization
Ø Green manuring.
Bacterization is a technique of seed dressing with bacteria.
Eg:azotobacter ,bacillus, rhizobium.
It has been known that bacteria can successfully be established in root region of plants which in turn improve the growth of host.
Eg;Bacterial fertilizers named azotobacterium containing cells of azotobacter and chrococcum.
Phospho bacterium containing cells of Bacillus megatherium and Phosphoticum can be used as fertilizers which increases upto 10-20%
In rhizosphere , bacteria secrete growth substances and antibiotic secondary metabolites which contribute to seed germination and plant growth.
RHIZOBIUM:
Rhizobium exist in symbiotic relationship with legumes.They fiix atmospheric nitrogen and thus not only increase the production of the inoculated crops but also leave a sufficient amt of nitrogen in the soil which benefits the subsequent crop.
Seven groups of rhizobium have been recognized for inoculating legumes in India.
v Inoculated with theeRhizobium leguminosarum
v Rhizobium japonicum
v Rhizobium trifoli
v Rhizobium melilothi
v Rhizobium phaseoli
v Rhizobium lupinci
v Rhizobium species
The nitrogen fixing ability of legumes inoculated with these rhizobium ranges from 50kg to 150kg/hectare.Hence to increase thi ability to fix atmospheric nitrogen following efforts are being made:
1) Efficient rhizobia for different crops and locations which are tolerant to various stresses like drought, temperature, increased or decreased PH are being isolated, maintained and used.
2) Hop+ gene is being used which helps in recycling of hydrogen produced during nitrogen fixation.
3)Strains deficient in nitrate reductase have improved nitrogen fixation ability.
RHIZOBIUM.
AZOTOBACTER:
Azotobacter Vinelandii is a free-living bacterium that can fix atmosferic nitrogen into the soil, being a great source to obtain a natural biofertilizer that can be used in the cultivation of most crops.
It is a great source of nitrogen to meet the needs of crops because also has the capabilities to cause a rejuvenation of soil microbiology to tap out the biological fixation of nitrogen.
Azotobacter is Gram negative bacteria, polymorphic i.e. they are of different sizes and shapes. Their size ranges from 2-10x1-2.5 m ., young cell possess peritrichous flegella and are used as locomotive organs. Old population of bacteria includes encapsulated forms and have enhanced resistant to heat, desication and adverse conditions. The cyst germinates under favourable conditions to give vegetative cells. They also produce polysachharides. Azotobacter spp.,are sensitive to acidic pH, high salts, and temperature above 350C.
There are four important species of Azotobacter viz. A.Chroococcum, A.agilis, A.paspali and A.vinelandii of which A.chroococcum is most commonly found in our soils.
Nitrogen fixation by Azotobacter:
The species of Azotobacter are known to fix on an average 10 mg.of N/g of sugar in pure culture on a nitrogen free medium. A maximum of 30 mg. N fixed per gram of sugar was reported by lopatina. However, Azotobacter is a poor competitor for nutrients in soil. Most efficient strains of Azotobacter would need to oxidise about 1000 kg of organic matter for fixing 30 kg of N/ha. This does not sound realistic for our soils which have very low active carbon status. Besides, soil is inhabitated by a large variety of otherr microbes, all of which compete for the active carbon.
BENEFITS:
· It improves seed germination and plant growth
· Azotobacter are tolerant to high salts.
· It can benefit crops by Nitrogen fixation, growth promoting substances, fungi static substances.
· Azotobacter is heaviest breathing organism and requires a large amount of organic carbon for its growth.
· It is poor competitor for nutrients in soil and hence its growth promoting substances, fungistatic substances.
· It thrives even in alkaline soils.
· Azotobacter is less effective in soils with poor organic matter.
AZOTOBACTER
PHOSPHATE SOLUBILIZING BACTERIA:
In the soil phosphate is present in the combined forms with Ca, Fe, Al etc and are insoluble in water.They are converted into soluble phosphates by the activities of microbes which are called phosphate solubilizers.eg:Bacillus megatherium,Psedomonas, Psedomonas putida.
Some fungi like aspergillus, pencillium are also phosphate solubilizers but have not been used in commericial preparation of bio fertilizers.
The phosphate solubilizers secrete many organic acids ike HCOOH, CH3COOH,Succinic acid, Propionic acid etc in the soil.These acids react with rock phosphate to make them soluble in water.Thus, they convert inorganic phosphate into soluble phosphate which can be utilized by crop plants.
These bio fertilizers reduce the use of phosphate fertilizers in agriculture.
ALGAL BIOFERTILIZERS:
This comprises mainly of blue green algae
The importance of blue green algae (cyanobacteria) os bio fertilizers were recognized as early as 1939.
Blue green algae constitute an important group of micro organism capable of fixing atmospheric nitrogen.They comprises unicellular,colonial and filamentous forms.
Most of the nitrogen fixing blur green algae belongs to the genera Anabene, Nostoc, Cytoneme, Plectonema etc.In general N2 fixation is associated with forms possessing heterocysts.
The process of application of blue green algal culture in fields as bio fertilizers is known as ALGALIZATION.
In water logged conditions., blur green algae such as Anabene, nostoc multiply, fix atmospheric nitrogen and release it into the surroundings in the form of aminoacids, proteins and other growth promoting substances.
The benefit from algalizatio is about 25-30kg/hectare/cropping season
SPIROGYRA:
It is a non living nitrogen fixing algae. Its inoculations severs as organic biomass for the growing rice plants.
Furthur, the mucilaginous sheath of the filaments of spirogyra is an abode of many micro organisms some of which may fix nitrogen.
ANABENA-AZOLLA:
Anabena is a blue green algae which exist in a symbiotic association wit azolla a pteridophytic plant
Both the hast and the symbiotic Anabena which reside on the dosal lobe at azolla leaves are capable of photosynthesis but the nitrogen requirement of the host are fulfilled by the symbiont through nitrogen fixation.
An intreasting feature of Azolla-Anabena association is that the symbiosis is maintained during the saprophytic and gametophytic cycles
Azolla mat is harvested and dried to use as green manure
There are 2 methods of application in the field:
a)Incorporation of Azolla in soil prior to rice plantation./
b)Transplantation of the rice followed by the water drawing and incorporation of Azolla.
Azolla is capable of producing about 900kg of nitrogen/hectare/year.
The daily nitrogen rate is as high as7 kg nitrogen/hectare
ANEBENA
LIMITATIONS:
There are certain limitations in using Azolla as bio fertilizers.
a)Azolla as a green manure crop is labour intensive
c) Otimum temperature is required for Azolla multiplication.
MYCORRHIZAE:
It is a symbiotic association of fungi with plant roots.
Fungus absorbs nutrients from the soil and releases it into the host cell and in turn host supplies the fungus with food requirements.
Mycorrhizae helps in growth of plants by inhibiting the growth of pathogenic bacteria present in the soil.
There are 2 types of mycorrhizae
1)ecto mycorrhiza
2)endo mycorrhiza.
ECTOMYCORRHIZA:
Ectomycorrhizas, or EcM, are typically formed between the roots of around 10% of plant families, mostly woody plants including the birch, dipterocarp, eucalyptus, oak,pine, and rose families and fungi belonging to theBasidiomycota, Ascomycota, and Zygomycota. Ectomycorrhizas consist of a hyphal sheath, or mantle, covering the root tip and a hartig net of hyphae surrounding the plant cells within the root cortex. In some cases the hyphae may also penetrate the plant cells, in which case the mycorrhiza is called an ectendomycorrhiza. Outside the root, the fungal mycelium forms an extensive network within the soil and leaf litter. Nutrients can be shown to move between different plants through the fungal network. Carbon has been shown to move frompaper birch trees into Douglas-fir trees thereby promotingsuccession in ecosystems. The ectomycorrhizal fungusLaccaria bicolor has been found to lure and kill springtailsto obtain nitrogen, some of which may then be transferred to the mycorrhizal host plant.
The first genomic sequence for a representative of symbiotic fungi, the ectomycorrhizal basidiomyceteLaccaria bicolor, has been published. An expansion of several multigene families occurred in this fungus, suggesting that adaptation to symbiosis proceeded by gene duplication. Within lineage-specific genes those coding for symbiosis-regulated secreted proteins showed an up-regulated expression in ectomycorrhizal root tips suggesting a role in the partner communication. Laccaria bicolor is lacking enzymes involved in the degradation of plant cell wall components (cellulose, hemicellulose, pectins and pectates), preventing the symbiont from degradind the host cells during root colonization.
ENDO MYCORRHIZA:
Endomycorrhiza are variable and have been further classified as arbuscular, ericoid, arbutoid, monotropoid, and orchid mycorrhizae. Arbuscular mycorrhizas, or AM (formerly known as vesicular-arbuscular mycorrhizas, or VAM), are mycorrhizas whose hyphae enter into the plant cells, producing structures that are either balloon-like (vesicles) or dichotomously-branching invaginations (arbuscules). The fungal hyphae do not in fact penetrate the protoplast (i.e. the interior of the cell), but invaginate the cell membrane. The structure of the arbuscules greatly increases the contact surface area between the hypha and the cell cytoplasm to facilitate the transfer of nutrients between them.
Arbuscular mycorrhizae are formed only by fungi in thedivision Glomeromycota. Fossil evidence and DNA sequence analysissuggest that this mutualism appeared400-460 million years ago, when the first plants were colonizing land. Arbuscular mycorrhizas are found in 85% of all plant families, and occur in many crop species. The hyphae of arbuscular mycorrhizal fungi produce the glycoprotein glomalin, which may be one of the major stores of carbon in the soil. Arbuscular mycorrhizal fungi have (possibly) been asexual for many millions of years and, unusually, individuals can contain many genetically different nuclei (a phenomenon called heterokaryosis). Many plants in the order Ericales form ericoid mycorrhizas, while some members of the Ericales form arbutoid and monotropoid mycorrhizas. All orchids are mycoheterotrophic at some stage during their lifecycle and form orchid mycorrhiza with a range of basidiomycete fungi.
Mycorrhizal innoculations stimulate rooting and growth and there by transplant survival of cutting and seedling which is essential for the successful reclamation and forestation programs.
Due to this beneficial attributes the mycorrhizae are widely used as bio fertilizer for improving the growth of agriculture and horticulture plants
Thanks :
http://vjahnavi57.blogspot.in/2010/11/bio-fertilizers.html
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.719.2177&rep=rep1&type=pdf
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