39588657 bio fertilizers

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Biofertilizers


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Definition

Biofertilizers includes selective microorganisms

like bacteria, fungi, algae which are capable offixing atmospheric N or convert insolublephosphate and other salts in the soil into formsavailable to plants.


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Nutrients are taken up primarily by theroots in the form of an aqueous solution

in the soil

Photosynthesis: CO2 + H2O carbohydrates (CHO) + O2

Major Cause: Nutrient

Deficiency In Soil


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Why Biofertilizers???

Disadvantages of chemical fertilizers: The chemical fertilizers are used for better crop yield

which are also providing N,P. But use of these fertilizers in excess of recommended

levels in order to ensure high yields(generally farmersdo),cause environmental pollution.

These environmental contamination & over supply ofnutrients can lead to negative consequences on humansand animals.

- Ingestion of nitrate can be toxic to humans. It cause eutrophication.


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Advantages

Biofertilizers are the microbial inoculants

contain unique and beneficial strains of soilmicrobes.

The Biofertilizers production cost is very low

On nutrient basis 1 tonne of Rhizobium

Biofertilizers is equivalent to 100 tonne of fertilizer nitrogen (Verma & Bhattacharyya,1991).


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Advantag

es

1. Biofertilizers are supplements to chemicalfertilizers.

2. They are cheap & can help to reduce fertilizer

consumption.3. They provide biological nitrogen directly to plants

4. They help in solubilization & mineralization ofother plants nutrients like phosphates.

5. They enhance plant growth due to release of hormones, vitamins, auxins and other growthpromoting substances.


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Advantag

es

6. On an average crop yield increases by 10-20percent with their use.

7. They control and suppress soil borne diseases

8. They help in the proliferation and survival ofbeneficial micro organisms in the soil

9. They improve soil properties and maintain soilfertility.

10. They are eco-friendly and pollution free.


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Types of biofertilizers Nitrogen fixers1. Symbiotic:Rhizobium, Frankia2. Non symbiotic:Azotobacter, Azospirillum,

Blue green algae,Azolla, Acetobacter

Phosphate supplier1. Phosphate solubiliser:Bacillus, Pseudomonas,

Aspergillus

2. Phosphate absorber: V.A.Mycorrhiza (VAMfungi)


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Types of biofertilizers

Sulphur supplier

1. Thiobacillus novellus, Aspergillus

Organic matter decomposer and microbial cellmass.

1. Cellulose decomposer, Lignin decomposer.


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Comparative overview of chemical fertilizer and Biofertilizers

Factors Chemical fertilizers Biological fertilizers

production Industrial, centralized Biological, small scale or

decentralized

Process chemical Biological

Raw materials and

energy budget

Fossil fuel & others imported, based on

non-renewable energy sources, energy

intensive

Atmospheric nitrogen for nitrogen

fixers, unavailable P for PSM and

VAM, Organic residues for compostdecomposing organisms.Indigeous

and local, based on renewable

energy sources very low energy bill.

Efficiency 40-45% for nitrogenous fertilizers for

upland crops and less than 33 % for

rice,25-33% or phosphatic fertilizers.

Heavy N losses due to leaching,

volatization and denitrification.P

availability decreased due to fixation.

About 90% efficiency. Losses due to

leaching, fixation are negligible.

Effect on

subsequent crop

For nitrogen- nil or low Residual effect for nitrogen

Pollution effect Exists due to discriminate use Pollution free


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Targeted All crops

Rhizobium: legumes,

BGA-Azolla: Rice,

Azotobacter, Azospirillum :Most cereals, cotton,

sugarcane

Shelf life long Short for bacteria, long for

BGA

Accessibility Affordable section Small and marginal farmers

Irrigation More useful to irrigated field Useful for both irrigated and

dry land farming

Cost High cost input Rs. 6.0 for 1

kg N, Rs. 14.0 for one kg

F2O5

Low cost input- 20 paise per

kg N through Rhizobium, 50

paise through BGA

Soil health Indiscriminate use

deteriorates the soil health

Improves the soil health


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Algal Biofertilizers

Nitrogen fixers

Non-symbiotic

Blue Green Algae FUNGAL BIOFERTILIZER

Phosphate solubilizers

Symbiotic Non-symbioticMycorrhizae Aspergillus

Penicilum


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Azotob

acter

Is free living nitrogen fixer

Isolation is carrried out from soil

near rhizosphere area. Is Gram negative cocobacilli,capsule

forming,motile,cyst former.

Forms soft, flat,milky white mucoid colonies on

Agar medium

Microscopic observation


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Azotobactercolonies on N-free medium

Azotobacter colonies are often slimy,

due to synthesis ofexopolysaccharide, andpigmented. A wet mount of anisolated colony off the plate at 1000Xmagnification. Note the large size ofthe cells. Both cysts (phase bright

ovals) and vegetative cells (phasedark bacilli) are visible.

Capsule formation byAzotobacter chroococcum


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Contributing plantnutrient

microorganisms Cropsbenefited

A) Nitrogen Symbiotic microbe:Rhizobium

Pulse legume:chickpea,lentil,moong,bean,cowpeaOil Legume:Soybean,groundnut

Azolla Rice

Azospirillum Sorghum,Rice,Wheat,maize,tomato,chilly

Azotobacter Vegetables:onion,bringal,tomato,c

abbageCereals:wheat,rice,maize,sorghum,sugarcane


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Phosphate Phosphorous, the master key element is known to be involved in

functions in the plant growth & development, photosynthesis,breakdown of sugar, energy & nutrient transfer within the plant &expression. Phosphorous nutrition benefits plant by producingdeeper & abundant roots. So supply of this element to plant isessential for achieving optimum crop yield.

It is supplied through phosphatic fertilizers, animal manures,phosphate solubilizing microorganisms.

The P content in average soil is about 0.05%(W/W).The variationbeing largely due to differences in weathering intensity & parentmaterial composition.

But only 0.1% of the total P is availble to plants because of its lowsolubility & its fixation in soil

Thus soil is rich in phosphorous which needs tobe harnessed.


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Phosphate Fertilizers

There are chemical fertilizers which are providing phosphate. Thesefertilizers are routinely applied to promote crop yields.

The phosphate in these fertilizers is initially available to the plantbut it rapidly reacts with soil & becomes progressively less availblefor plant uptake.This is known as chemical fixation of phosphorous.

So now phosphate solubilizing micro-organisms(PSM) dissolvinginterlocked phosphates appear to have an importance.

Many fungi, bacteria are potential solubilizers of

bound phosphates in soil


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Mechanism ofphosphate solubilization

1) Solubilization by production of organic acid

2) Solubilization by phosphatase

Production ofacid: The major microbiological means by which insoluble phosphorus

compound are mobilized by the production of organic acid which isaccompanied by acidification of medium.

The organic & inorganic acids convert tricalcium phosphate to thedi- & monobasic phosphates which got available to plants.

Examples of organic acids citric acid, fumaric acid, malic acid,lactic acid, gluconic acid, ketoglutonic acid, glyoxylic acid.

Solubilization by phosphatase:The liberation of P from organic phosphate compounds is mainly dueto the action of enzymes of esterase type.

Besides these two mechanisms the production of chelating substancesH2S, CO2,mineral acids, siderophores and ion-exchangemechanisms are also involved in P solubilization by PSMs.


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Both free-living and mutualistic species found in this

group. The mutualistic species may be found in rootnodules of legumes where they are important for properplant nutrition. Along with the Cyanobacteria thesenitrogen fixing bacteria contain the metabolic pathways

which can "fix" atmospheric nitrogen N2 into reduced

forms (nitrate, nitrite, and ammonia) that higher plantscan use to make amino acids and therefore proteins.There are 5 genera -- e.g., Rhizobium sp.. Thephotograph below shows Rhizobium sp. in the rootnodules of a bean plant.


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Need of nitrogen fixation ? ? ? ? ?

The earths atmosphere contains around 78.08%[N2] nitrogen gas.

It cannot be used in this form by most livingorganisms until it has been fixed, that is reduced(combined with hydrogen), to ammonia.

Nitrogen is required by all living organisms forthe synthesis of proteins, nucleic acids and other

nitrogen-containing compounds. Biological nitrogen fixation is the reduction ofatmospheric nitrogen to ammonia by micro-organisms in soil.


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Nitrogen C

ycle

The 2 major processes of N2 transformation are: Nitrification:NH4

+NO3

- :

NH4+NO2-NO2

-NO3

-

By bacteria e.g. Nitrobacter,Bacillus,Paracoccus,Pseudomonas.

Denitrification: NO3-N2

By bacteria e.g.Azotobacter, Clostridium andRhizobium.


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Nitrogen Fixation

N2 is the most stable form of nitrogen and highenergy is required to break the N-N triple bond.

Therefore only microorganisms can fix nitrogen

N2 + 8H+

+8e-

2NH3 + H2 N2 gas is the greatest reserve of nitrogen. The productivity of many environs is limited by

the short supply of nitrogenous compounds.

Nitrogen fixation is important to agricultureand legumes such as soybean can fixatmospheric nitrogen.


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Denitrification

Denitrification is the reduction ofnitrates toN2 or NO2.

This process is detrimental because it removes

nitrogen the environment. This is of particular importance to agriculturewhere nitrate fertilizers are used.

If anoxic condition develop e.g. water logged

soil. The nitrate is remove from the soil bydentrification. What do you understand by the term anoxic conditions?


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Ammonification The decomposition of organic nitrogen

compounds such as amino acids and nucleotidesis called ammonification.

In the soil much of this NH3 is converted toamino acids by plants.

Some NH3 is lost by evaporation especially indense animal populations.

Globally this constitutes 15% of N2 released tothe atmosphere.


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Nitrification Nitrification is the oxidation ofNH3 to NO3

-bynitrifying bacteria.

The nitrates produced is readilyassimilatedby plants.

Nitrate is soluble and is quickly leached from thesoil.

NH4+ is +vely charged and will adhere to vely

charged soil (clay) particles.

NH4+ is extensively used in nitrogenousfertilizers.

Denitrification consumes N2while nitrificationproduces it.


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Nitrogen Fixation by Legumes

The association ofnitrogen fixing bacteriawith legumes is one of the most importantbacteria plant interaction.

Nitrogen fixing legumes include, soybean,bean, pea, cloverand alfalfa are plants withbeans in pods.

Nitrogen fixing bacteria in plants include:

RhizobiumBradyrhizobiumMesorhizobiumAzorhizobium

30000 X magnified image of Rhizobium


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Various groups ofRhizobium

Rhizobium spp. Cross inoculation grouping

R. leguminosarum Pea group

R. phaseoli Bean group

R. trifoli Clover group

R. meliloti Alfalfa group

R. Llupini Lupini group

R. japonicum Soyabean group

R. spp Cowpea group

Tricalcium phosphate solubilizing activityof Rhizobium sp. strain U9709-SC. Thestrain was grown on Illmer and Shinneragar medium supplemented withCa3(PO4)2 at 27

OC in the dark for 3 days(right) and 12 days (left). Clear zonesaround colonies reveal the areas where the

tricalcium phosphate has been solubilized.


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Nitrogen Fixation

The symbiotic relationship between plant andnitrogen fixing bacteria results in the formationof a root nodule.

In the nodule N2 is converted by the enzymenitrogenase to ammonia.

The ammoniais used in the synthesis ofamino acids and other cellular components.

Under normal conditions neitherRhizobium northe plant can fix nitrogen.


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Nitrogen Fixation

Rhizobium can only fix N2 (diazotrophy) undermicroaerophilific (reduced O2) conditions.

This is because O2 is needed byRhizobiumbut O2 also

inhibits nitrogenase. Rhizobia are soil bacteria that fix nitrogen after

becoming established inside root nodules of legumes(Fabaceae)

Rhizobia require a plant host; they cannotindependently fix nitrogen.

Morphologically, they are generally gram negative,motile, non-sporulating rods.


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Leghemoglobin

In the nodule O2 level is reduced byleghemoglobin.

Leghemoglobin is synthesized only afterinteraction of the plant andRhizobium.

90% of legumes will fix nitrogen.

However each nitrogen fixing bacteria will onlyassociate with certain legumes.


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Leghemoglobin


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Steps in Nodule Formation1. Recognition of the correct partner by both plant

and bacteria.2. Attachment of the bacteria to the plant root.

3. Invasion of the root hairby bacteria throughthe formation of an infection thread.4. Growth to the main rootvia the infection

thread.5. Formation ofbacteroids (deformed bacteria

cells) and development of nitrogen fixingstate.6. Continued division of plant and bacteria cell and

formation ofmature root nodule.


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Steps in Formation ofRoot Nodule


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Problems with Biofertilizers

Strict aseptic precaution is required duringproduction of microbial fertilizer.Contamination is a common problem during

microbial mass production. Microbial fertilizer are sensitive to sunlight

exposure. They get killed if exposed for long timein sunlight.

Microbial fertilizer must be used within sixmonths after production when stored at roomtemperature. They can be used within two yearsif stored at chilling temperature.


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Problems with Biofertilizers

Efficiency of microbial fertilizer is markedlydependent on soil character e.g. moisturecontent, pH, temperature organic matter andtypes of resident micro-organisms. When these

factors are unfavorable microbial fertilizer maynot be effective in increasing the soil fertility.


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39588657 bio fertilizers

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