BIOFERTILIZERS AND THEIR ECO-FRIENDLY USE IN AGRICULTURE

INDEX


CONTENTS PAGE


 Abstract 4
 Introduction 5
 Need for use of biofertilizer 5
 Types
• Rhizobium 5 - 6
• Azospirillum 6 -7
• Blue green algae 7 - 8
• Azolla 8
• Phosphate Solubilising Biofertilizer 8- 9
• Azotobacter 9
• Mycorrhiza 9 - 11
 Advantages of using biofertilizer 11
 Precautions 11 - 12
 Conclusion 12
 References 12










ABSTRACT

With the introduction of green revolution technologies the modern agriculture is getting more and more dependent upon the supply of synthetic inputs (mainly fertilizers), which are products of fossil fuel . Adverse effects are noticed due to the excessive and imbalanced use of these synthetic inputs. Dependence on chemical fertilizers for future growth would mean further loss in soil quality and possibilities of water contamination This situation has lead to identifying harmless inputs like biofertilizers. Use of such natural products like biofertilizers in crop cultivation will help in safeguarding the soil health and also the quality of crop products.This can be relatively cheap and convenient for use.Biofertilizers are gaining momentum recently due to the increasing emphasis on maintenance of soil fertility , minimize environmental pollution .



















INTRODUCTION
Biofertilizers are used to improve the fertility of the land by using biological wastes and biological wastes do not contain any chemicals which are harmful to the living soil. Biofertilizers generate plant nutrients like nitrogen and phosphorus through their activities in the soil and make available to plants in gradual manner.They are beneficial in enriching the soil with microorganisms which increases nutrient quality of soil and also impart strength to combat with diseases.The main sources of biofertilizers are bacteria, fungi and cynobacteria. The most striking relationship that these microorganisms have with plants is symbiosis in which the partners derive benefits from each other. The most important microorganisms which have symbiotic relationship with plants are mycorrhiza, rhizobium and cyanobacteria. These delivers number of benefits including plant nutrition, disease resistance and tolerance to adverse soil and climatic conditions.
NEED FOR USE OF BIOFERTILIZERS: First, the increase in the use of fertilizers leads to increased crop productivity. Second, because increased usage of chemical fertilizer leads to damage in soil texture and raises other environmental problems. Therefore, the use of biofertilizers is both economical and environment friendly.
TYPES: Biofertilizers include the following types: 1. Symbiotic Nitrogen Fixers Rhizobium spp. 2. Asymbiotic Free Nitrogen Fixers (Azotobacter) 3. Azospirillum 4. Algae Biofertilizers (Blue Green Algae or BGA in association with Azolla). 5. Phosphate Solubilising Bacteria. 6. Mycorrhizae. 7. Organic Fertilizers
Rhizobium spp.: These are gram positive soil bacteria and symbiotic nitrogen fixer which assimilates atmospheric nitrogen and fixes in the root nodule, formed in the roots of leguminous plants and also in some nonleguminous plants. The root nodulating rhizobia are as: R . leguminosarum nodulates pea ; R . phaseoli nodulates bean and Bradyrhizobium nodulates soybean. But Azorhizobium caulinodans is one such rhizobial species that nodulates the stems of Sesbania rostrata.
Rhizobium cells contain genes for nitrogen fixation(nif genes) on a megaplasmid.The bacteria enter the roots through root hairs ; interaction is progressing through several steps and it ultimately leads to nodule formation.Inside the nodule many bacterial cells changing into nondividing bacteroids, which produces nitrogenase enzyme which reduces
atmospheric nitrogen to ammonia.
RHIZOBIAL ROOT NODULES (Refrence:www.indiamart.com/manidharmabiotech/biofertilizers.html)
Usually the biofertilizers or strains of Rhizobia are used as seed inoculants during sowing.The seeds are inoculated with Rhizobium culture before sowing. In beginning Rhizobium cultures were based on agar-agar medium which were replaced by soil based ones but now peat and lignite are used .Phosphate is needed for a better efficiency of rhizobial biofertilizer. This biofertilizer is recommended for pulse legumes such as red gram, pea, black gram; oilseed legumes like soybean and groundnut; fodder legumes like barseem.
Uses: 1.Rhizobium can fix 50-200 kgs N/ha in one crop season. 2. It can increase yield up to 10-35%. 3. Due to rhizobial activities, the root hairs and nodules secrete a mucous substance which enhances the soil fertility and growth of the plant. 4. The enzyme nitrogenase will reduce the molecular nitrogen to ammonia which is readily utilized by the plant. 5. By means of seed treatment, the germination of seeds gets stimulated and in turn increase crops yield potential.
Azospirillum: It is the associate symbiotic nitrogen fixer, aerobic free living which makes the atmospheric nitrogen available to various crops. This nitrogen-fixing bacterium when applied to the soil undergoes multiplication in billions and fixes atmospheric nitrogen in the soil. Nitrogen fixation in the rhizosphere through the action of nitrogenase enzyme. The Scientists of Indian Agricultural Research Institute, New Delhi have isolates strains of Azospirillum from the roots of grasses, rice , sorghum and maize.
Uses: 1. Azospirillum sp. have the ability to fix 20-40 Kgs N/ha 2.It results in average increase in yield of 15-30%. 3. It also results in increased mineral and water uptake. 4. It also promotes root development and vegetative growth. 5. Fortification of the soils occurs with bacterial metabolites and by secreting growth promoters.
It is recommended for Paddy, Millets, Oilseeds, Fruits , Vegetables, Sugarcane, Banana, Coconut, Oil palm, Cotton, Chilly, Lime, Coffee , Tea, Rubber, Flower, Spices, Herbs, Ornaments, trees etc
Blue green algae : Blue Green Algae(Cyanobacteria) are photosynthetic, free living and prokaryotic organisms which fix nitrogen asymbiotically but some cyanobacteria are known to form symbiotic associations.Examples of cyanobacteria are Anabaena , Nostoc , Plectonema etc.Cyanobacteria produce nitrogenase and nitrogen fixation occurs in specialized structures called heterocysts. Also heterocysts act as oxygen proof compartments which protect nitrogenase from oxygen inactivation.In India the soil conditions in rice fields provide suitable environment for growth of cyanobacteria. Cyanobacterial biofertilizers can be prepared by farmers in their own field.For this open tanks of galvanized iron sheets or bricks and cement are made and cyanobacteria of required strain are cultured in this tank. A mixture of sieved soil, super phosphate, sodium molybdate and water is added into tank then mixture is thoroughly mixed and allowed to stand for 24 hrs. Then starter culture of required strain of cyanobacteria is sprinkled on surface of water and allowed to stand for 15-20 days. Then thick serum of algal mass is collected and allowed to dry.
Uses: Cyanobacteria add growth promoting substances including Vitamin B 12 and it also improves soil aeration and water holding capacity. It can provide 20-30 kg of biologically fixed nitrogen per hectare under normal conditions which can be doubled if optimum amounts of phosphate and molybdenum are available in soil. . It provides partial tolerance to pesticides and fungicides.
BGA is also supplied with Azolla (an aquatic fern), which harbors Anabaena azolle (a BGA) in leaf cavities, providing symbiotic association.
Azolla: It is an aquatic heterosporus fern which contains an endophytic cyanobacterium Anabaena azollae in its leaf cavity. It is widely used in Vietnam as biofertilizer for rice. Dr. P.K. Singh at CRRI (Cuttak) has done work on mass cultivation of Azolla and its use in rice and other fields. Mass cultivation of Azolla is done as : firstly microplots are prepared in which sufficient water is added.Optimum pH (8. 0) and temperature (14- 30ºC) should be maintained. Then microplots are inoculated with fresh Azolla and an insecticide furadon is used to check the attack of insects. After 3 weeks Azolla mat is harvested and fresh Azolla is inoculated in same microplot to repeat the inoculation. Azolla mat is dried to use as green manure. Also Azolla shows tolerance against heavy metals e.g. A . pinnata absorbs heavy metals into cell walls and vacuoles due to specific metal resistant enzymes. It can also be incorporated as green manure in rice field near the polluted areas where heavy metal concentration is present.
Uses: It is mostly used in rice fields where water is available for its growth and multiplication. It is supplemented with 8-20 kg phosphate per hectare.It improves the height of rice plants , number of tillers , grains and straw yield.There is 50% higher yields by using Azolla as biofertilizer.
Phosphate Solubilising Biofertilizer : Phosphorus both native in soil and applied in inorganic fertilizers becomes mostly unavailable to crops because of its less mobility and solubility.Phosphate solubilising microorganisms present in soil are Pseudomonas, Bacillus, Micrococcus, Aspergillus, Fusarium etc. They convert non available inorganic phosphorus present in soil into an available form utilizable by crop plants. The bacteria Bacillus, Thiobacillus can produce iron chelating substances siderophores which chelate the iron present in the root zone. This iron becomes non available to harmful microorganisms and crop plants are protected from them. They can also secrete organic acids and lowers the pH in their vicinity to bring about solubilization of bound phosphates in soil.
Uses: 1.By the hydrolytic activities of these organic acids the insoluble phosphorus in rendered soluble in the soil. 2. Fortification of the soils with bacterial metabolites. 3. These organisms play a major role in the solubilization and uptake of native and applied phosphorus. 4. The introduction of efficient phosphate solubilizers in the rhizosphere of crops increases the availability of phosphorus by secreting organic acids like Citric, Oxalic, Succinic, Tartaric, Malic acids in the soil environments. 5. It can increase crop yield upto 200-500 kg/ ha.
Azotobacter: It uses organic matter present in soil to fix nitrogen asymbiotically.It has been observed that inoculation of soil or seed with Azotobacter causes increase in yield of crops. This biofertilizer is mainly used in Russia and many European countries under the name Azotobacterin. The application of this is upto 20% increase in yield of crops such as wheat, barley, maize, carrot, cabbage etc.
Mycorrhizal fungi : The term Mycorhiza was coined by Frank in 1885.It is a distinct morphological structure which develops as a result of mutualistic symbiosis. It is the symbiotic association between plant roots and soil fungus.The kinds of mycorrhizae are:
1. Ectomycorriza: Ectomycorrhiza arc found on the roots of forest trees (e.g. pine, oak, beech, eucalyptus, etc.).In general root hairs are absent on roots of some higher plants. Therefore roots are infected by mycorrhizal fungi and form a mantle. The hyphae grow intercellularly and develop Hartig net in cortex. So a bridge is established between the soil and root through the mycelia. They absorb nitrogen, phosphorus, potassium and calcium. and produce growth promoting substances i.e. cytokinins. The major functions which ectomycorrhizae perform are: absorption of water; solubilisation of complex organic molecules into simplex inorganic nutrients then their absorption and transfer to roots; protection of plants from attack of inciting pathogens by secreating antimicrobial substances.
2. Endomycorrhiza: In this association fungus does not form an external sheath or mantle. The fungus lives in the intercellular spaces as well as intracellularly in the cortical cells of roots. Only a small portion of fungus lives outside the root.Endomycorrhiza are found in the roots of most fruits and other horticultural crops e.g. coffee, pepper, cardamom, and betelvine. They particularly help in phosphorus nutrition. They also produce growth promoting substances and offer resistance against pathogens.

VesicularArbuscularMycorrhiza (Refrence:www.indiamart.com/manidharmabiotech/biofertilizers.html)
One of the important type of endomycorrhizae, VAM plays a great role in inducing plant growth. VAM is highly versatile and colonizes 85% of the plant families. It penetrates the roots, forms arbuscules and vesicles in the cortical cells of the roots Vesicles are thick walled swollen structures and arbuscules are branched hautorial branches of mycelium .They serve as food storage organs of the fungus. VAM can be produced on a large scale by pot culture technique.


Uses: 1.VAM fungi enhances water uptake in plants. 2. They increase resistance in plants and reduce the effects of pathogens and pests on plants. 3. The mychorrhiza penetrates the roots, mobilizes & supplies phosphorus and other micronutrients to the plants. 4.VAM fungi reduce plant response to soil stress.5. Mycorrhizal plants show higher tolerance to high soil temperaturesand heavy metal toxicity.
Genetically Engineered Microbes: These are microorganisms into which a gene or genes have been introduced using recombinant DNA technology. They can be tailored to fulfill specific needs and perform functions, which their natural counterparts can never perform. They can be used for crop protection by control of insects e.g. Clavibacter containing B. thrugenesis cry gene, fungal diseases (e.g. Pseudomoas expressig chitiase gee from Serratia). They degrade nonbiological wastes and detoxify toxic wastes and also show enhanced nitrogen fixation by amplication of nif genes in R .melilotii.

ADVANTAGES OF USING BIOFERTILIZERS IN AGRICULTURE:
1. It is a low cost and easy technique.
2. The biofertilizers increase 15-35% additional yield in most of vegetable crops.
3. Besides fixing atmospheric nitrogen, cyanobacteria synthesize and excrete several growth hormones (auxins and ascorbic acid) and vitamins which enhance seed germination and growth of crop plants.
4. They do not cause atmospheric pollution and increase soil fertility.
5. Some biofertilizers excrete antibiotics and thus act as pesticides.
6. They improve physical and chemical properties of soil such as water holding capacity, buffer capacity etc.
7. Some of the biofertilizers enhance crop yield even under ill irrigated conditions where chemical fertilizers are of not much advantage.
8. They are ecofriendly and pose no danger to the environment.
PRECAUTIONS THAT SHOULD TAKEN WHILE USING BIOFERTILIZERS:
1. Biofertilizer packets need to be stored in cool and dry place also away from direct sunlight and heat. 2. Right combinations of biofertilizers have to be used. 3. As Rhizobium is crop specific, one should use for the specified crop only. 4. Other chemicals should not be mixed with the biofertilizers. 5. The packet has to be used before its expiry, only for the specified crop and by the recommended method of application. 6. Biofertilizers are live product and require care in the storage 7.Both nitrogenous and phosphatic biofertilizers are to be used to get the best results. 8.It is important to use biofertilizers along with chemical fertilizers and organic manures.
CONCLUSION:
Bio-fertilizers (also known as microbial inoculants) improve soil fertility and enhance nutrient uptake and water uptake in deficient soils, thereby aiding in better establishment of plants. Bio-fertilizers also secrete growth subustances and antifungal chemicals, as well as improve seed germination and root growth. Thus, the use of bio-fertilizers will effectively enrich the soil and will cost less than chemical fertilizers, which harm the environment and deplete non-renewable energy sources.
REFRENCES:
www.icrisat.org/vasat/learning_resources/organicFAQs/biofertilizer.htm www.ikisan.com/links/up_riceBiofertilizers.shtml#top www.pugwash.org/reports/ees/cuba2004/02%20pugwash/07_ondina www.molecular_plant_biotehnology.info/use_of_microbes_in_industry http://www.indiamart.com/manidharmabiotech/biofertilizers.html. http://megapib.nic.in/fertilizer_biofertilizer.html Biotechnology Expanding Horizons By B.D Singh (Kalyani Publishers 2007) A Textbook of Biotechnology By R.C Dubey (Published by S.Chand)