Biofertilizers

Definition

Biofertilizers includes selective microorganisms like bacteria, fungi, algae which are capable of fixing atmospheric N or convert insoluble phosphate and other salts in the soil into forms available to plants.

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

solution in the soil

Photosynthesis: CO2 + H2O carbohydrates (CHO)

+ O2

Major Cause: Nutrient Deficiency

In Soil

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 farmers do),cause environmental pollution.

• These environmental contamination & over supply of nutrients can lead to negative consequences on humans and animals.

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

Advantages

•Biofertilizers are the microbial inoculants contain unique and beneficial strains of soil microbes.

•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).

Advantages1. Biofertilizers are supplements to chemical

fertilizers.2. They are cheap & can help to reduce

fertilizer consumption.3. They provide biological nitrogen directly to

plants4. They help in solubilization & mineralization

of other plants nutrients like phosphates.5. They enhance plant growth due to release of

hormones, vitamins, auxins and other growth promoting substances.

Advantages6. On an average crop yield increases by

10-20 percent with their use.7. They control and suppress soil borne

diseases8. They help in the proliferation and

survival of beneficial micro organisms in the soil

9. They improve soil properties and maintain soil fertility.

10.They are eco-friendly and pollution free.

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

Blue green algae, Azolla, Acetobacter

•Phosphate supplier1. Phosphate solubiliser: Bacillus,

Pseudomonas, Aspergillus2. Phosphate absorber: V.A.Mycorrhiza (VAM

fungi)

Types of biofertilizers

•Sulphur supplier1. Thiobacillus novellus, Aspergillus

•Organic matter decomposer and microbial cell mass.

1. Cellulose decomposer, Lignin decomposer.

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 compost decomposing 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

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

Algal Biofertilizers Nitrogen fixers

Non-symbiotic

Blue Green Algae FUNGAL BIOFERTILIZER

Phosphate solubilizers Symbiotic Non-symbiotic Mycorrhizae Aspergillus Penicilum

Azotobacter

•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

Azotobacter colonies on N-free medium

Azotobacter colonies are often slimy, due to synthesis of exopolysaccharide, andpigmented. A wet mount of an isolated colony off the plate at 1000X magnification. Note the large size of the cells. Both cysts (phase bright ovals) and vegetative cells (phase dark bacilli) are visible.

Capsule formation by Azotobacter chroococcum

Contributing plant nutrient

microorganisms Crops benefited

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,cabbageCereals:wheat,rice,maize,sorghum,sugarcane

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 producing deeper & abundant roots. So supply of this element to plant is essential 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 variation being largely due to differences in weathering intensity & parent material composition.

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

Thus soil is rich in phosphorous which needs to be harnessed.

Phosphate Fertilizers

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

• The phosphate in these fertilizers is initially available to the plant but it rapidly reacts with soil & becomes progressively less availble for plant uptake.This is known as chemical fixation of phosphorous. So now phosphate solubilizing micro-organisms(PSM) dissolving interlocked

phosphates appear to have an importance.

Many fungi, bacteria are potential solubilizers of bound phosphates in soil

Mechanism of phosphate solubilization

1) Solubilization by production of organic acid2) Solubilization by phosphatase

Production of acid: • The major microbiological means by which insoluble phosphorus

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

• The organic & inorganic acids convert tricalcium phosphate to the di- & 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

due to the action of enzymes of esterase type.

Besides these two mechanisms the production of chelating substances H2S, CO2,mineral acids, siderophores and ion-exchange mechanisms are also involved in P solubilization by PSMs.

Both free-living and mutualistic species found in this group. The mutualistic species may be found in root nodules of legumes where they are important for proper plant nutrition. Along with the Cyanobacteria these nitrogen fixing bacteria contain the metabolic pathways which can "fix" atmospheric nitrogen N2 into reduced forms (nitrate, nitrite, and ammonia) that higher plants can use to make amino acids and therefore proteins. There are 5 genera -- e.g., Rhizobium sp..  The photograph below shows Rhizobium sp. in the root nodules of a bean plant.

Need of nitrogen fixation ? ? ? ? ?

•The earth’s atmosphere contains around 78.08% [N2] nitrogen gas.

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

•Nitrogen is required by all living organisms for the synthesis of proteins, nucleic acids and other nitrogen-containing compounds.

•Biological nitrogen fixation is the reduction of atmospheric nitrogen to ammonia by micro-organisms in soil.

Nitrogen Cycle•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 and

Rhizobium.

Nitrogen Fixation•N2 is the most stable form of nitrogen and

high energy 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 agriculture and legumes such as soybean can fix atmospheric nitrogen.

Denitrification•Denitrification is the reduction of

nitrates to N2 or NO2.•This process is detrimental because it

removes nitrogen the environment.•This is of particular importance to

agriculture where nitrate fertilizers are used.

•If anoxic condition develop e.g. water logged soil. The nitrate is remove from the soil by dentrification.

• What do you understand by the term “anoxic conditions”?

Ammonification•The decomposition of organic

nitrogen compounds such as amino acids and nucleotides is called ammonification.

• In the soil much of this NH3 is converted to amino acids by plants.

•Some NH3 is lost by evaporation especially in dense animal populations.

•Globally this constitutes 15% of N2 released to the atmosphere.

Nitrification•Nitrification is the oxidation of NH3 to NO3

- by nitrifying bacteria.

•The nitrates produced is readily assimilated by plants.

•Nitrate is soluble and is quickly leached from the soil.

•NH4+ is +vely charged and will adhere to –

vely charged soil (clay) particles.•NH4

+ is extensively used in nitrogenous fertilizers.

•Denitrification consumes N2 while nitrification produces it.

Nitrogen Fixation by Legumes•The association of nitrogen fixing bacteria

with legumes is one of the most important bacteria plant interaction.

•Nitrogen fixing legumes include, soybean, bean, pea, clover and alfalfa are plants with beans in pods.

•Nitrogen fixing bacteria in plants include:RhizobiumBradyrhizobiumMesorhizobiumAzorhizobium

30000 X magnified image of Rhizobium

Various groups of RhizobiumRhizobium 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 activity of Rhizobium sp. strain U9709-SC. The strain was grown on Illmer and Shinner agar medium supplemented with Ca3(PO4)2 at 27 OC in the dark for 3 days (right) and 12 days (left). Clear zones around colonies reveal the areas where the tricalcium phosphate has been solubilized.

Nitrogen Fixation

•The symbiotic relationship between plant and nitrogen fixing bacteria results in the formation of a root nodule.

• In the nodule N2 is converted by the enzyme nitrogenase to ammonia.

•The ammonia is used in the synthesis of amino acids and other cellular components.

•Under normal conditions neither Rhizobium nor the plant can fix nitrogen.

Root Nodules

Nitrogen Fixation

• Rhizobium can only fix N2 (diazotrophy) under

microaerophilific (reduced O2) conditions.

• This is because O2 is needed by Rhizobium but 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 cannot independently fix nitrogen.

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

Leghemoglobin

•In the nodule O2 level is reduced by leghemoglobin.

•Leghemoglobin is synthesized only after interaction of the plant and Rhizobium.

•90% of legumes will fix nitrogen. •However each nitrogen fixing bacteria

will only associate with certain legumes.

Leghemoglobin

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 hair by bacteria through

the formation of an infection thread.4. Growth to the main root via the infection

thread.5. Formation of bacteroids (deformed bacteria

cells) and development of nitrogen fixing state.

6. Continued division of plant and bacteria cell and formation of mature root nodule.

Steps in Formation of Root Nodule

Steps in Formation of Root Nodule

Problems with Biofertilizers•Microbial fertilizers are supplementary to

chemical fertilizers but not substitute to it. Microbial fertilizers, usually cause 20 to 30 per cent increase inn crop production. They do not cause marked increase in productivity like chemical fertilizer.

•Specific fertilizer are to be used for specific crops. This is more applicable to symbiotic microorganisms. If non specific Rhizobium is used as fertilizer they do not cause rood nodulation and increase in crop production.

Problems with Biofertilizers•Strict aseptic precaution is required

during production 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 time in sunlight.

•Microbial fertilizer must be used within six months after production when stored at room temperature. They can be used within two years if stored at chilling temperature.

Problems with Biofertilizers•Efficiency of microbial fertilizer is

markedly dependent on soil character e.g. moisture content, pH, temperature organic matter and types of resident micro-organisms. When these factors are unfavorable microbial fertilizer may not be effective in increasing the soil fertility.

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