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BIOFERTILIZERS

The ‘Biofertilizers’ or ‘microbial inoculants’ can be generally defined as preparations containing live or latent cells of efficient strains of nitrogen fixing, phosphate solubilizing or cellulolytic microorganisms which are used for application to seed, soil or composting areas with the objective of increasing the numbers of such microorganisms, for better growth of plants and higher yield.

The earliest records indicate that Romans and Aryans had many manuals for farmers to improve the cultivation of crops. For example, the enhanced production of cereals could be achieved only by rotation of crops. This enhances the nitrogen fixation by the presence of Rhizobia in soils. The idea of inoculation was indirectly known to our ancestors when they transferred large amounts of soil from areas where leguminous crops were flourishing to areas where they were less luxuriant.

The modern day intensive crop cultivation requires the use of chemical fertilizers. But these fertilizers are not only in short supply but are also expensive. Therefore, the current trend is to explore the possibility of supplementing chemical fertilizers with organic ones, more particularly biofertilizers of microbial origin. Microbial processes are not only quick but also less energy consuming than industrial processes.

Development of microbial fertilizers: Microbial inoculants are carrier based preparations containing beneficial microorganisms in viable state intended for seed or soil application and designed to improve soil fertility. They also help in plant growth by increasing the number and biological activity of desired microorganism in the root environment.

Following the success of legume inoculants all over the world, carrier based Azotobacter or non- leguminous crops are becoming increasingly popular.

1895. Nobbe and Hiltner introduced a laboratory grown culture of rhizobia called Nitragin grown on solid medium containing extracts of leguminous plants, gelatin, sugar and asparagines. In this medium, 17 different inoculants for important leguminous crops were produced. Later production of biofertilizer came into practice all over the world for the enhanced of crops.

Types of Biofertilizers:I

1. Rhizobium biofertilizer (inoculant)

2. Azospirillum biofertihzer

3. Azotobacter biofertilizer

4. Blue green algal biofertilizer (BGH)

5. Azolla biofertilizer

6. Phosphate solubilizing microorganisms as biofertilizer.

7. ) Vesicular - Arbuscular Mycorrhiza (VAM) as a biofertilizer

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1. Rhizobium biofertilizer

Rhizobia are soil bacteria. They have an ability to fix atmospheric nitrogen. They make a symbiotic association with legumes and some nm-legumes like Parasponia. Rhizobium bacteria enter into the roots through root hairs. They release certain stimulatory root exudates and form nodules . Inside the root, rhizobia invade expanded cells of cortex, and then differentiate into nitrogen-forming "bacteroids". Neither the plant nor the bacteria can fix nitrogen when live separately. The nodules filled with pink sap (leghaemoglobin pigment) are called the effective nodules. This pigment maintains the rhythm of oxygen supply to the bacteria and helps the activity of nitrogenase enzyme. The nitrogenase is responsible for reduction of nitrogen to ammonia in the process of nitrogen fixation. This bacterium is classified into two genera, Rhizobium and Bradyrhizobium.The amount of atmospheric nitrogen fixed varies with the strains of rhizobium, plant species and environmental factors.

The Rhizobium inoculant (biofertilizer) is a microbial preparation containing living cells of Rhizobium Spp. The manufacture of Rhizobial biofertilizer requires the following steps.

a) Isolation of Rhizobium b) Identification c) Cultivation and mass production d) Storage Methods of field application.

Classification of Rhizobium Biofertilizers

Cultivation and mass production:

After isolation and identification of Rhizobial cultures, the culture is used for mass production. Rhizobia is usually maintained by sub culturing at regular intervals in Yeast Extract mannitol agar (YEMA) medium two criteria are used for selection of strain. a) ability to form nitrogen fixing nodules and b) ability of nodule formation under wide range of field conditions.

Storage (carrier based inoculum for storage): After fermentation the cultured Rhizobial cells can be added to the carriers like sedge peats or lignite to store the

inoculum. The carrier is used to preserve the inoculum in a viable condition. Peats are ground into fine powder. The powder is neutralized with CaCO3 and autoclaved at 15 psi pressure for 4 hours. After cooling, the powder is mixed with the diluted Rhizobial culture. In this method, 3 x 10 8 Rhizobia are preserved in a gram of peat. Sometimes lignite is used to preserve the inoculum for about one year. After mixing with carrier, the mixture is cured in trays for 2-5 days and packed in polythene bags and stored at 4°C.

Rhizobium Species Principal Plant Inoculated Rhizobium leguminosarum

Biovar phaseoli Phaseolus (Bean) Biovar viceae Vicea (Vetch)

Biovar trifolii Trifolium (Berseem)Rhizobium meliloti Melilotus (Senji)

Trigonella (Fenugreek) Medicago (Lucerne)

Rhizobium loti Lotus (Trifoils)

Bradyrhizobium japonicum Glycine (Soybean)Bradyrhizobium species Lupinus (Lupin)

Vigna (Cowpea)

Cicer (Gram)

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Methods of field application: Carrier based cultures are mixed with minimum amount of water to form slurry. To this slurry is added sugar (10% sucrose) or gum arabic which enhances the survival of Rhizobia on seeds. The seeds are added to the slurry and mixed well, so that the seeds take uniform coating on the surface of the seed coat. The seeds are dried in shade and sown immediately.

Methods of field application: Carrier based cultures are mixed with minimum amount of water to form slurry. To this slurry is added sugar (10% sucrose) or gum arabic which enhances the survival of Rhizobia on seeds. The seeds are added to the slurry and mixed well, so that the seeds take uniform coating on the surface of the seed coat. The seeds are dried in shade and sown immediately.

Classification of Rhizobium Biofertilizers

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Rhizobium Species Principal Plant Inoculated Rhizobium leguminosarum

Biovar phaseoli Phaseolus (Bean) Biovar viceae Vicea (Vetch)

Biovar trifolii Trifolium (Berseem)Rhizobium meliloti Melilotus (Senji)

Trigonella (Fenugreek) Medicago (Lucerne)

Rhizobium loti Lotus (Trifoils)

Bradyrhizobium japonicum Glycine (Soybean)Bradyrhizobium species Lupinus (Lupin)

Vigna (Cowpea)

Cicer (Gram)

2) Azospirillum Inoculum

AzospirillumThis is a free living or non -symbiotic bacteria (does not form nodules but makes association by living in the rhizosphere). Azospirillum species establish an association with many plants particularly with C, plants such as maize, sorghum, sugarcane, etc. It is the most common organism and can form associativesymbiosis on a large variety of plants. Beijerinck in 1925 reported a nitrogen fixing bacterium under the name of Spirillum lipoferum. and et al., (1978) later on renamed this organism as Azospirillum (Nitrogen fixing Spirillum).Azospirillum is recognized as a dominant soil microbe.Azospirillurn also forms a close associative symbiosis with the higher plants. The bacteria live on root surface, sometimes also penetrates into the root tissues but do not produce any visible nodule or out growth on the root tissue. They fix nitrogen from 10 to 40 kglha. The Azospirillum inoculation helps better vegetative growth of the plants, saving nitrogenous fertilizers by 25-30%. So far only four species of Azospirillum have been identified. They are A. lipoferum, A. brasilense, A. amazonense, A. iraquense. In Indian soils A. brasilense and A. lipoferum are very common. Inoculation with Azospirillum have resulted enhanced yields of different vegetable crops. Mass Culture and Maintenance of Azospirillum : The selected strain of bacteria is cultured in a medium containing ammonium chloride. The ammonium chloride allows the cells to grow in a large number, while it prevents the nitrogen fixation during the culture of the microbes.

For the large-scale production of Azospirillum, large- sized flasks are used. The sterile liquid medium (malate medium) is distributed into the flasks. The liquid medium is treated with a sufficient amount of ammonium chloride. A sample of Azospirillum is inoculated into the medium. The culture is incubated at 35°C for 3 days. Sometimes, the culture is kept on a shaker system to facilitate cell culture. The cultured inoculum is stored in a carrier-based inoculum used directly to fertilize the field.

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Carrier-based inoculums for Storage: Powdered farmyard manure (FYM) and soil or farmyard manure alone or farmyard manure plus charcoal are used to preserve the inoculum for storage. The inoculum is mixed with the carrier and allowed to dry in air. The inoculum is stored at 4°C. This method is used to store the organisms for about 31 weeks. The farmyard manure with, soil carrier shows better response than the other types of carriers. The viability of cells can be measured by the cell-counting method or by the colony-counting method.

Methods of Application of Azospirillum:

a) The cultured inoculum is mixed with a carrier mixture (FYM and soil in 1: 1 ratio) and stored at room temperature. This carrier-based inoculum is used in seed treatment.

b) Twelve grams of carboxy methylcellulose is added to 1 liter of inoculum. It acts as a pelleting agent, and causes the sticking of inoculum on the seeds. Thus the inoculum is spread over the field along with the seeds, during sowing.

c) The inoculum is sprinkled directly over the seeds on a sheet of polythene paper; then the seeds are mixed well for the proper mixing of inoculum and the seeds.

d) The roots of the plants are immersed in diluted inoculum just before transplantation.

3) Azotobacter Inoculum

Azotobacter is a free-living, non-symbiotic, nitrogen-fixing bacterium. It is a soil-inhabiting bacterium. It includes six species such as Azotobacter beijerinckii, A. paspali, A. chroococcum, A. haplophilus, A. vinelandii and A. miscellus. All these species effectively fix the atmospheric nitrogen in the soil.

Features of Azotobactor Azotobacter contributes to the moderate benefits. Azotobacter is heaviest breathing organism and requires a large amount of organic carbon for its

growth. It is poor competitor for nutrients in soil. It can benefit crops by Nitrogen fixation, release of growth promoting substances, and fungicidic

substances. Azotobacter is less effective in soils with poor organic matter content. It improves seed germination and plant growth. It thrives even in alkali soils.

Isolation of Azotobacter : Azotobacter is isolated from the soil. The different steps involved in the isolation of Azotobacter are suggested below:

a) The soil sample is collected and mixed with the nitrogen-free medium to prepare a soil slurry.

b) The slurry is serially diluted with the liquid medium to bring about the growth of the Azotobacter colonies.

c) The culture is incubated at 300C for 3 days. Azotobacter produces mucoid colonies on the agar medium.

d) These milky, mucoid colonies are tested to determine the presence of nitrogenase activity by using acetylene reduction assay method. The selected strain is mass-cultured in a large container.

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Culture of Azotobacter: The isolated Azotobacter strain is cultured in large-sized flasks containing Jenson’s medium. For the large scale production, it is cultured in batch fermenters. The culture flasks are kept on a shaker to facilitate the better growth of the bacteria.

Carrier-based Inoculum:

a) The culture inoculum is mixed with powdered peat soil or farmyard manure and dried in the air. The dried inoculum is used for field trials. Sometimes, lignite is also used as a carrier. The Azotobacter inoculum is kept at 4°C for long-term storage.

b) Sometimes the powdered carriers are neutralized with calcium carbonate and autoclaved for proper sterilization. The sterilized mixture is then mixed with the Azotobacter inoculum and allowed to dry in the air before storage.

Methods of Application of Azotobacter:

a) Seed Treatment: The cultured inoculum is diluted with water and the seeds are kept dipped in the inoculum overnight. The seeds are removed from the inoculum in the early morning and sown in the main field after sometime. The remaining slurry is directly poured over the nursery bed or in the agricultural field.

b) Sometimes, the seeds are spread on a polythene sheet and the inoculum is sprinkled over the seeds for the mixing of the inoculum with the seeds. The inoculum-coated seeds are then dried in the air before sowing.

c) Seedling Treatment: In this method, the inoculum is diluted with water and the roots of the seedling are kept dipped in the inoculum for about 10-15 minutes. By this method a sufficient amount of Azotobacter cells are added to the root system of plants such as rice plants.

d) Application in Rice Field: A required amount of inoculum is mixed with well- decomposed cattle dung (farmyard manure). Then this mixture is properly mixed with soil. The resulting carrier based inoculum is directly used in the cultivation of rice. Generally 2 kg of inoculum is mixed with 20 - 25kg of well- decomposed cattle dung and 20-25 kg of soil. This mixture is enough to manure I hectare of rice field.

Importance of Azotobacter as a Biofertilizer:

a) The treatment of Azotobàcter with 75% of recommended level of nitrogen fertilizers gives almost as much yield as the treatment of 100% recommended level of nitrogen fertilizers.

b) Besides this, Azotobacter synthesises biologically active substances, such as nicotinic acid, panthothenic acid, pyridoxin, biotin, gibberellic acid, etc. These substances stimulate the growth of higher plants.

c) It provides a favorable micro environment to the root system of higher plants and induces the better growth of the roots. Thus it participates in the growth of root systems in higher plants.

Acetobactor

Acetobactor diazotrophicus is a newly discovered nitrogen fixing bacteria associated with sugarcane crop. This

bacterium belongs to the alpha group of proteobacteria. It was isolated from leaf, root, bud and stem samples

of sugarcane. Acetobator is located in apoplastic fluid of sugarcane stem and to some extent in xylem vessels.

It is an acid and high salt tolerant and sucrose loving bacteria which can fix up to 200 kg nitrogen per hectare.

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Under field condition, the yield of sugarcane increased after its inoculation. Productions of auxins and

antibiotic type substance have also been notice after its application.

Frankia

Frankia is actinomycetes which also fixes atmospheric nitrogen. It forms a symbiotic association by forming

root nodules in some non-leguminous trees such as Casuarina and Alnus. The wasteland soil fertility can be

improved by growing Casuarina. Frankia makes casuarina tree suitable for agro-forestry system in nitrogen

deficient soils. In the beginning of nodulation, Frankia occurs as small lateral swelling on roots and then

develops into new lobes at their apices and form cluster coralloid structure. Its inoculation enhances growth,

nodulation, nitrogenase activity of nodule and nodule dry weight of Casuarina and Alnus plants.

4) The Blue Green Algae or Cyanobacteria (BGA)

The blue green algae (cyanobacteria) are also able to fix the atmospheric nitrogen in the soil. They fix 20-30 kg of nitrogen in a hectare per annum. Blue green algae such as Anabaena, Aulosira, Tolypothrix, Oscillator, etc; actively fix nitrogen in the soil. In addition to nitrogen fixation, the BGA also release vitamin B12, auxins, etc. which enhance the growth of higher plants. Thus they form an effective biofertilizer in agriculture.

Preparation of Blue Green Algal lnoculum: Blue green algae are cultured in open vessels exposed to air. The different stages of BGA inoculum preparation are:

a) Zinc or iron tray the size of 2 x 1 x 3 m is used for the culture of BGA. The tray is filled with 10-12 kg of sieved nice soil 750 gms of superphosphate and 5 gm of sodium molybdate. Water is added to the mixture to keep the medium wet.

b) The pH of the soil solution is tested and adjusted to the neutral pH.

c) A starter culture of BGA is then sprinkled over the soil mixture and the tray is kept in the open sunlight for about 10-20 days for establishing proper growth.

d) Regular watering is essential during the culture of the BGA.

e) Sometimes mosquitoes breed over the soil mixture. The breeding of mosquitoes can be prevented by treating the mixture with 1 ml of parathion or 25 grams of carbofuron per tray. These chemicals prevent the invasion of egg - laying mosquitoes in the culture tray.

f) Owing to their rapid growth, the blue green algae cover the entire surface of the soil mixture. The algal biomass is then separated from the soil and air-dried. The dried biomass is powdered and stored in polythene bags for future use.

BGA Culture in Open Field:

a) The field is ploughed well and levelled properly for the culture of BGA. Five Kg of BGA inoculum is spread over the surface of the soil per one cent area.

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b) The field is watered to a height of 2.5 cm from the soil in order to facilitate the growth of the algae.

C) Two Kg of super phosphate is sprayed over the surface of the soil; it induces the rapid growth of BGA. The clay soil requires weeks for establishing the proper growth of BGA, while the sandy soil requires 3 - 4 weeks for establishing the proper multiplication of BGA.

d) Snails, mosquitoes, etc. are checked by applying parathion or carbofuron over the field.

e) When sufficient growth f BGA is achieved, the field is ploughed well for the proper mixing of BGA with the soil. Then the field is used for agriculture.

Methods of BGA Application: The powdered BGA mixture is spread over the agricultural field. The application of BGA after one week of transplantation of seedlings of rice gives more beneficial result, because BGA will be able to receive more sunlight. Such rice plants grow well in the field by consuming the nitrogen fixed by the BGA. The application of BGA in the field increases the yield of crops.

5) Azolla Biofertilizer

Azolla is a water fern. It forms symbiotic association with the blue green algal Anabaena azollae. It fixes the atmospheric nitrogen in the soil; the soil nitrogen is readily consumed by the plants growing in the field. The nitrogen fixation takes place at all stages of its development.

Cultivation of Azolla:

Small nurseries of 100 sizes are generally preferred for the culture of Azolla. It is helpful to prevent the erosion of seeds from the culture field owing to the forces of wind and water. Then Azolla inoculum is spread over the nursery beds; generally I gram of Azolla inoculum is enough to culture Azolla in I m space in the field. The pH of the soil solution of the nursery bed should be adjusted to 8 which is ideal for the growth of the Azolla. The acidic soils are not suitable for the growth of Azolla. The pH can be properly modified by the addition of lime to the field. The temperature of the nursery should be adjusted to 14-35°C which favors the growth of the Azolla. Insects and pests are prevented by spraying carbofuron over the field; generally 1 kg of carbofuron is used per hectare. The standing water of 10 cm in the field increases the growth of the Azolla. Generally 8 kg of super phosphate is used to fertilize one hectare of nursery; it induces better growth of the Azolla in the nursery. Such Azolla culture method yields 8 tons of Azolla /hectare within 20 days.

Methods of Application of Azolla

a) Azolla is used as green manure in rice cultivation. The Azolla biomass is added to the field and ploughed repeatedly for the proper mixing of Azolla in the soil. Then the seedlings are transplanted to the field.

b) Azolla inoculum is also sown over the rice field along with seeds. Sometimes the seedlings are treated with the inoculum before transplantation. Azolla fixes nitrogen in the soil. Hence it is used in agriculture as a biofertilizer.

Importance of Azolla

a) It is used as green manure in the cultivation of rice.

b) It reduces the used of nitrogen fertilizers.

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c) It reduces the development of weeds and their spreading over the rice field.

6) Phosphobacteria Inoculum

Phosphobacteria are a group of microbes which convert the rock phosphates or inorganic phosphates into soluble organic phosphates. The organic phosphate exists in the form of mineral acids or organic acids which are readily utilized by the higher plants for their growth.

In the soil, phosphates are present in combined forms with calcium, iron, aluminum, etc. They are insoluble in water and are converted into the soluble phosphates by the activity of microbes like. Penicillium digitatum, Bacillus circulans, B. subtilis, B. megatherium, Aspergillus niger, A. flavus, Fusarium oxysproum, Xanthomonas, Pseudomonas, Flavobacterium, Escherichia intermedia, etc. which act as phosphate solubilizer in the soil. They secrete some organic acids like formic acid, acetic acid, lactic acid, succinic acid, propionic acid, etc. in the soil. These acids react with rock phosphates and make them soluble in water. Sometimes they release hydroxyacids which also convert the rock phosphates into organic soluble phosphates.

They reduce the use of phosphate fertilizers in agriculture. The different organic acids secreted by these microbes also have some influence on the growth of higher plants.

7) Vesicular - Arbuscular Mycorrhiza (VAM) as a biofertilizer

These are a group of fungi which form symbiotic association with the roots of higher plants. They form endomycorrhiza in the roots of angiosperms. They infect a number of agricultural crops like rice, cotton, etc. and horticultural crops like citrus, tobacco, sugarcane and apple. They also infect the plantation crops like rubber, coffee, tea, papaya, etc. and produce mycorrhiza in their roots.

The Vesicular-orbicular mycorrhizal fungi (VAM Fungi) include 6 genera: Glomus, Gigaspora, Acaulospora, Entrophospora, Sclerocysits and Scutellospora, distinguished on the basis of their sporocarps. They are distributed all over the world except in water-logging areas. They produce hyphae with vesicles and arbuscules in the root cortex and increase the absorption surfaces of the root system for the uptake of more mineral nutrients from the soil.

Salient Features of VAM Fungi

a) They are filamentous, symbiotic fungi.

b) They form symbiotic association with the roots of higher plants.

c) They belong to the class zygomycetes

d) They are intracellular, obligate endosymbionts.

e) They produce special structures like vesicles (swollen structures) and arbuscules (branched tree like hyphae) inside the host cells.

f) They produce fruiting bodies (sporocarps) around the roots.

g) They increase the absorptive surface of the root system Importance of VAM Fungi in Agriculture

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VAM fungi effectively infect a lot of agricultural crops and play certain important roles in agriculture. The following are some important applications of VAM fungi in agriculture.

a) The VAM fungi increase the absorption of Phosphates by agricultural crops. The dry weight of shoots increases with the increase of VAM-fungi infection on the root system of plants. The increased dry weight is due to the consumption of more phosphates by plants.

b) Uptake of Zn by plants is enhanced through VAM fungi infection. The VAM-fungi infected seedlings have more Zn in their tissues (Examples: maize, wheat, potato, etc.)

c) VAM fungal infection increases the uptake of water from the soil. Thus it helps to overcome the water stress.

d) VAM fungal infection also increases the uptake of sulphur from the soil. Red clover and maize absorb more sulphur when their roots are infected by VAM fungi.

e) VAM fungi also increase the concentration of cytokines and chloroplasts in the infected plants.

f) When the VAM fungi infected plants are under shade, the concentration of photosynthates in the plants becomes decreased. In such a condition, VAM fungi provide nutrition to the infected plants. Thus they protect plants against stress.

Mechanism of Action

The VAM forms an association with plant roots. It penetrates in the root cortex and spreads around the roots

of the plant. As the name indicates, they posses sac like structure called vesicules which stores phosphorus as

phospholipids. The other structure called arbuscule helps bringing the distant nutrients to the vesicules and

root.

Actions of Mycorrhiza

1) Enhances the feeding areas of the plant root is as the hyphae spreads around the roots.

2) Mobilizes the nutrients from distantance to root.

3) Stores the nutrients (sp. phosphorus).

4) Removes the toxic chemicals (example : phenolics) which otherwise hinder nutrient availability.

5) Provide protection against other fungi and nematodes.

METHODS OF BIOFERTILIZER INOCULATION (APPLICATION)

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The biofertilizers can be inoculated on seeds as well as in the roots of different crop plants under ideal

conditions. They can also be applied directly to the soil.

Seed Inoculation

This is the most common practice of applying biofertilizers. In this method, the biofertilizers are mixed with 10

per cent solution of jaggary. The slurry is then poured over the seeds spread on a cemented floor and mixed

properly in a way that a thin layer is formed around the seeds. The treated seeds should be dried in the shade

overnight and then they should be used. Generally, 750 gram of biofertilizer is required to treat the legume

seeds for one hectare area.

Root and Seedling Treatment

The seedling roots of transplanted crops are treated for half an hour in the solution of biofertilizers before

transplanting in the field. In this method, seedlings required for one acre are inoculated using 2-2.5 kg

biofertilizers.For this in a bucket having adequate quantity of water is taken and biofertilizer is mixed properly.

Roots of the seedlings are then dipped in this mixture so as to enable roots to get inoculum. These seedlings

are then transplanted. This method has been found very much suitable for crops like Tomato, Rice, Onion,

Cole Crops and flowers.

Soil Application

This method is mostly used for fruit crops, sugarcane, and other crops where localized application is needed.

At the time of planting of fruit trees, 20 g of biofertilizer mixed with compost is to be added in the ring of one

sapling. We may add same quantity of biofertilizer in the ring soil of the seedling after it has attained maturity.

Sometime, the biofertilizers are also broadcasted in the soil but we may require four to ten times more bio

fertilizers. Before broadcasting, the inoculants should be incubated with the desired amount of well

decomposed granulated FYM for 24 hours. The FYM acts as food and adjuvant (carrier) for biofertilizers.

Self Inoculation or Tubez Inoculation

This method is exclusively suitable for application of Azotobactor. In this method, 50 litres of water is taken in

a drum and 4-5 kg of Azotobacter biofertilizer is added and mixed properly. Planting materials required for

one acre of land are dipped in this mixture. Similarly, if we are treating the potato, then the tubers are dipped

in the mixture and planting is done after drying the materials in the shade.

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ADVANTAGES

There are many advantages of using the biofertilizers.

They form an important association with other soil microbes and help in casertent nutrient supply. However,

we may visualize some basic advantages as listed below:

Fixes atmospheric nitrogen.

Increase availability or uptake of nutrients through solubilization or increased absorption.

Stimulate plant growth through hormonal or antibiotics action or by decomposing organic waste.

They are cheap, hence, reduced cost of cultivation.

Improves soil properties and sustaining soil fertility.

Lead to soil enrichment.

Are compatible with long term sustainability.

Build up soil fertility in the long term.

Curtails the requirement of inputs.

They are eco-friendly and pose no damage to the environment.

DISADVANTAGES

As such there is no harmful impact of biofertilizers if it is used properly some constraints:

Specific to the plants.

Rhizobiurn spp. culture doesn't work well in high nitrate tolerant strains of soybean.

The acceptability of biofertilizers has been rather low chiefly because they do not produce quick and

spectacular responses.

Require skill in production and application.

Difficult to store.

CONSTRAINTS IN BIOFERTILIZERS

Biofertilizers are not popular because of many difficulties. Some of them are as follows :

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Inadequate popularity is due to that they can not show instant and dramatic response like fertilizers.

Inadequate awareness about its use and benefits.

Lack of promotion, extension and insufficient publicity.

Lack of availability of quality products in time to the farmers in rural areas.

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Pass word:biofertilizer