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BIOFERTILIZERS

Dr. Dr. SubhenduSubhendu DattaDatta

Sr. ScientistSr. Scientist

CIFE, Kolkata CentreCIFE, Kolkata Centre

Background:Background: Why bioWhy bio--fertilizers?fertilizers?

�� With the introduction of green revolution technologies With the introduction of green revolution technologies the modern agriculture is getting more and more the modern agriculture is getting more and more dependent upon the steady supply of synthetic inputs dependent upon the steady supply of synthetic inputs (mainly fertilizers) which are products of fossil fuel (mainly fertilizers) which are products of fossil fuel (coal+ petroleum). (coal+ petroleum).

�� Excessive dependence of modern agriculture and the Excessive dependence of modern agriculture and the supply of these synthetic inputs and the adverse effects supply of these synthetic inputs and the adverse effects being noticed due to their excessive and imbalanced being noticed due to their excessive and imbalanced use has compelled the scientific fraternity to look for use has compelled the scientific fraternity to look for alternatives.alternatives.

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(i). Availability and cost of commercial fertilizers(i). Availability and cost of commercial fertilizers

�� Demand is much higher then the availability. Demand is much higher then the availability.

�� It is estimated that by 2020, to achieve the targeted It is estimated that by 2020, to achieve the targeted production of 321 million tones of food grain, the production of 321 million tones of food grain, the requirement of nutrient will be 28.8 million tones, while requirement of nutrient will be 28.8 million tones, while their availability will be only 21.6 million tones being a their availability will be only 21.6 million tones being a deficit of about 7.2 million tones. deficit of about 7.2 million tones.

�� Increasing costs are getting unaffordable by small and Increasing costs are getting unaffordable by small and marginal farmers. marginal farmers.

(ii) Effect of Chemical fertilizers in soil and (ii) Effect of Chemical fertilizers in soil and

environmentenvironment

� Excessive and imbalanced use of chemical fertilizers has adversely affected the soil causing decrease in organic carbon, reduction in microbial flora and fauna of soil, increasing acidity and alkalinity and hardening of soil.

� Moreover, excessive use of nitrogenous and phosphaticfertilizers are contaminating water bodies (eutrophication) thus affecting fish fauna and causing health hazards for human beings and animals.

� Production of chemical fertilizers adds to the pollution.

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�� To overcome the deficit in nutrient supply and to To overcome the deficit in nutrient supply and to

overcome the adverse effects of chemical cultivation, it overcome the adverse effects of chemical cultivation, it

is suggested that efforts should be made to exploit all is suggested that efforts should be made to exploit all

the available resources of nutrients under the theme of the available resources of nutrients under the theme of

integrated nutrient management. integrated nutrient management.

�� Under this approach the best available option lies in the Under this approach the best available option lies in the

complimentary use of complimentary use of BiofertilizersBiofertilizers, organic manures in , organic manures in

suitable combination of chemical fertilizers.suitable combination of chemical fertilizers.

What are bioWhat are bio--fertilizersfertilizers

� “Biofertilizer is a substance which contains living microorganisms which, when applied to seed, plant surfaces, or soil, colonizes the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host Plant [Vessey, J.K. (2003). Plant growth promoting rhizobacteria as biofertilizers. Plant Soil 255: 571-586].

� This definition separates biofertilizer from organic manure.

� The latter contains organic compounds which directly, or by their decay, increase soil fertility.

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�Likewise the term biofertilizer should not be used interchangeably with the terms, green manure

�Not all plant growth promoting rhizobacteria(PGPR) can be considered biofertilizers.

�Bacteria that promote plant growth by control of deleterious organisms are biopesticides, but not biofertilizers.

� Similarly bacteria can enhance plant growth by producing phytohormones and are regarded as bioenhancers, not biofertilizer.

� The importance of cyanobacterial biofertilizerswas recognized as early as 1939. Since then good deal of literature on these aspects has appeared.

� Although biofertilizers are now being used in agriculture fields, it can equivocally be stated that biofertilizers may also be used in fish culture practices.

� Field studies shown that about 30 kg N/ha can be saved by the use of cyanobacterial biofertilizers.

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�� Indian DefinitionIndian Definition -- BiofertilizersBiofertilizers are ready to use live are ready to use live formulates of such beneficial microorganisms which on formulates of such beneficial microorganisms which on application to seed, root or soil mobilize the availability application to seed, root or soil mobilize the availability of nutrients by their biological activity in particular, and of nutrients by their biological activity in particular, and help build up the microhelp build up the micro--flora and in turn the soil health flora and in turn the soil health in general. in general.

Leguminous oilseed Crops: Soybeans

and peanut

Leguminous pulses: Arhar, Letils,

Mung, Urad, Pea, Cowpea, Gram,

Bio-fertilizer pack

Benefits of Benefits of biofertilizersbiofertilizers

�� Increase crop yield by 20Increase crop yield by 20--30%30%

�� Replace chemicalReplace chemical N & P by 25 %N & P by 25 %

�� Stimulate plant growthStimulate plant growth

�� Activate soil biologicallyActivate soil biologically

�� Restore natural fertilityRestore natural fertility

� Increases soil organic matter and maintains a good soil texture.

� Environmentally friendly - Don’t pollute the environment � Cheaper than synthetic fertilizers

� Believed to have growth promoting substances.�� Provide protection against drought and some soil borne diseasesProvide protection against drought and some soil borne diseases

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Types of Types of

BiofertilizersBiofertilizers

For Nitrogen:For Nitrogen:

�� RhizobiumRhizobium for legume cropsfor legume crops

�� Azotobacter/AzospirillumAzotobacter/Azospirillum for non legume cropsfor non legume crops

�� AcetobacterAcetobacter for sugarcane onlyfor sugarcane only

�� BGA and BGA and AzollaAzolla for low land paddy & for low land paddy & aquaultureaquaulture

For PhosphorousFor Phosphorous

�� PhosphatikaPhosphatika for all crops to be applied with for all crops to be applied with RhizobiumRhizobium, , AzotobacterAzotobacter, , AzospirillumAzospirillum and and AcetobacterAcetobacter

For enriched compostFor enriched compost

�� CellulolyticCellulolytic fungal culturefungal culture

�� PhosphotikaPhosphotika and and AzotobacterAzotobacter cultureculture

Most biofertilizers belong to one of

these two categories:

(a). Nitrogen fixing

(a). Phosphate solubilising.

METHOD OF APPLICATIONMETHOD OF APPLICATION

�� Seed treatment :Seed treatment :Suspend 200 gm N Suspend 200 gm N biofertilizerbiofertilizer and 200 and 200 gmsgms PhosphotikaPhosphotika in 300in 300--400 ml of 400 ml of water and mix thoroughly. Mix this paste with 10 kg seeds & dry water and mix thoroughly. Mix this paste with 10 kg seeds & dry in shade. in shade. Sow immediately.Sow immediately.

�� Seedling root dip:Seedling root dip:For vegetables 1 kg each of two For vegetables 1 kg each of two biofertilisersbiofertilisers be mixed in sufficient be mixed in sufficient quantity of water. Dip the roots of seedlings in this suspensionquantity of water. Dip the roots of seedlings in this suspension for 30for 30--40 40 min before transplanting.min before transplanting.For paddy make a bed in the field and fill it with water. Mix For paddy make a bed in the field and fill it with water. Mix biofertilisersbiofertilisers in in water and dip the roots of seedlings for 8water and dip the roots of seedlings for 8--10 hrs.10 hrs.

�� Soil treatment:Soil treatment:Mix 4 kg each of Mix 4 kg each of biofertilisersbiofertilisers in 200 kg of compost and leave it overnight. in 200 kg of compost and leave it overnight. Apply this mixture in the soil at the time of sowing or plantingApply this mixture in the soil at the time of sowing or planting..In plantation crops apply this mixture near root zone and cover In plantation crops apply this mixture near root zone and cover with soil. with soil.

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Nitrogen fixing biofertilizers

� Free-living or symbiotic bacteria and blue-green algae (Cyanobacteria) fix atmospheric gaseous nitrogen as ammonia and release it, increasing the fertility of soil and water.

� These include Rhizobium, Azotobacter, Acetobacter, Azospirillum, Blue Green Algae (BGA) and Azolla.

�While Rhizobium, A. azollae requires symbiotic association to fix nitrogen, others can fix nitrogen independently.

� Anabaena azollae living in leaf cavities of Azolla (aquatic

fern) are very efficient nitrogen fixers, and contribute about

500 kg N/ha/year.

Phosphate solubilising biofertilizersbiofertilizers

� Phosphate solubilising micro-organisms (PSM)

secrete organic acids which enhance the uptake of

phosphorus by plants by dissolving rock phosphate

and tricalcium phosphates.

� PSMs (e.g. PhosphatikaPhosphatika)) are particularly valuable as they are not crop specific and can benefit all crops.

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Composting bio-fertilizers

o Compositing biofertilizers are used for hastening the process of composting and for enriching its nutrient value.

o Composting process is enhanced by enzymes secreted by microorganisms (Cellulolyticellulolytic fungal culture)fungal culture) to hydrolysepectins, xylans, hemicellulose, cellulose releasing beneficial micronutrients for the plants.

Rhizobia (Soil bacteria of the genus Rhizobium)

produces root nodules in legumes.

Legume/Rhizobium Nodules are Red. This is due to

the production of Leghaemoglobin which sequesters

oxygen. This helps to create a low oxygen

environment.

The enzyme which fixes nitrogen (Nitrogenase) needs

an anaerobic environment.

Nitrogen fixing biofertilizers

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� Another microsymbiont with nitrogen fixing capacity the principal genus of microbes is Frankia.

�� MMorphology of Frankia is similar to that of actinomycetes and produces nodules in woody non-legumes, like Alnus, Casuarina, Myrica etc. Many of these are "pioneer" species which colonize barren sites.

� These nodules fix more atmospheric nitrogen than legume/RhizobiumNodules..

Root nodules of Alnus

�� Some of these are alien species like Some of these are alien species like MyriMyricaca,, grows much faster grows much faster

than native competitors, and they alter the soil nitrogen levthan native competitors, and they alter the soil nitrogen levels els

markedly compared to native stands. markedly compared to native stands.

AzollaAzolla--Anabaena azollae relationshiprelationship

o An Azolla plant floating on the surface of the water is roughly triangular or circular in shape and rarely exceeds 3–4cm (except in the species Azolla nilotica).

o The cyanobacterium Anabaena azollae occurs as filaments located on the stem apexes of Azolla(aquatic fern) and inside the leaf cavities inSymbiotic associationSymbiotic association, which are inoculated during their formation with some Anabaena from the apex.

Reference: C. Van Hove and A. Lejeune

(2002). Biology And Environment: Proceedings of

the Royal Irish Academy, Vol. 102B (1): 23–26.

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The Azolla–A.

azollae association can develop on a

medium devoid of

nitrogen compounds

because of the ability

of A. azollae to reduce N2 to NH3.

Some of the

ammonia is supplied

to the fern, andthe fern supplies the

cyanobacterium with

photosynthetic

assimilates.

Morphology of Azolla stem (longitudinal section).

1. Stem;

2. Stem apex;

3. Apical Anabaena colony without heterocysts;

4. Other bacteria;

5. Leaf primordium;

6. Young leaf;

7. Branched hair;

8. Single hair;

9. Upper leaf lobe;

10. Lower leaf lobe;

11. Leaf cavity (showing a central gaseous region and a peripheral mucilaginous region);

12. Involucre;

13. Indusia;

14. Microsporocarp;

15. Microsporangia;

16. Megasporocarp;

17. Megasporangium;

18. Akinetes of Anabaena;

19. Vegetative cell of Anabaena;

20. Heterocyst.

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Importance of Importance of AzollaAzolla–A. azollae symbiosis

� The Azolla–A. azollae symbiosis is has long been used by farmers, mainly in Asia, as feed for their animals and as green manure.

� Azolla is one of the most nutritive aquatic plants, owing to its high crude protein and carotenoid contents (anthocyanine ) and generally good amino-acid profile.

� It can be incorporated into the feed of fish, pigs, poultry, rabbits and even humans.

� A number of laboratory and field studies have shown beyond any doubt the beneficial effect of Azolla as an organic nitrogen fertiliser, mainly in terms of increasing rice grain yield.

� The presence of an Azolla mat on the surface of the water body has been shown to significantly reduce weed development, limit evapotranspiration, reduce volatilisation of applied N fertilisers and purify water.

� Recent research has focused on the use of Azolla in integrated farming systems, mainly rice–fish–Azolla and pig–poultry–fish–Azolla.

Azotobacter species are free-living (mostly root associated), aerobically nitrogen fixing bacteria.

Nostoc, Calothrix, Gloeotrichia, Stigonema, etc are free-living aerobically nitrogen fixing Cyanobacteria.

In addition, Vesicular Arbuscular Mycorhizae (VAM fungi) are free-living soil forms that increase nutrient uptake (specially by converting organic phosphorus into inorganic phosphorus), plant growth, nodulation and nitrogen fixation in legumes.

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� In coastal areas of some countries, seaweeds are also used

as biofertilizers.

� However, all these life forms may be grown artificially and

inoculated in seed, root or soil as biofertilizer.

� The nitrogen fixers releases nitrogen during their life time

and also add other elements after their death and decay,

essential for the growth of crops.

1. Azolla

2. Phosphatase bacteria

3. Phosphate solubilizing bacteria

4. Nitrogen fixing bacteria

5. Nitrogen fixing cyanobacteria

6. Enriched compost

Biofertilizers generally used in

Aquaculture

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What is Azolla?

� Azolla is a dichotomously branched (dichotomy

is a mode of branching by repeated bifurcation) free floating aquatic fern which is naturally available mostly on moist soils, ditches marshy ponds and is widely distributed in tropical belt of India.

� The shape of Indian species is typically triangular measuring about 1.5 to 3.0 cm in length 1 to 2 cm in breadth.

1. Azolla…

Roots emanating from growing branches remained suspended in water. The dorsal lobe which remains exposed to air is having a specific cavity containing its symbiotic partner, a Blue Green Algae (BGA), the Anabaena Azolae.

The fern is capable of fixing atmospheric nitrogen in the soil in the form of NH4

+ and becomes available as a soluble nitrogen for the wet land rice crop, which is the major cereal for the people of the North East.

Owing to the poor economic conditions of the farmers of the North Eastern States, rice crop is mostly grown under natural soil fertility with minimum inputs and amelioratives.

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Azolla…

�But for taking a good crop of rice, judicious application of nutrients is necessary.

�Besides, this, the farmers of the state of Meghalayaand other north eastern states have apathy in using chemical fertilizers in crop production.

�For sustainable crop production, there is a practice to supply some quantity of nutrients through organic manure, viz; FYM and composted plant residues and bio-fertilizers.

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Azolla…

In the context of depletion of soil fertility and high prices ofchemical fertilizer, it has become imperative to use biofertilizer which is a cheaper and renewable source of low cost plant nutrient and playing a major role in Integrated Plant Nutrient Supply System.

Use of Azolla fern as a bio-fertilizer is advocated to minimize the dependency of chemical fertilizer.

Azolla supplements nitrogen to rice crop by fixing atmospheric nitrogen in the soil for crop growth, crop production and maintain soil fertility.

Economic Value

On dry weight basis Azolla contains the following chemical

compositions:

Nitrogen : 5.0 %

Phosphorous : 0.5 %

Potassium : 2.0-4.5 %

Calcium : 0.1-1.0 %

Magnesium : 0.65 %

Manganese : 0.16 %

Iron : 0.26 %

Crude Fat : 3.0-3.3 %

Sugar : 3.4-3.5 %

Starch : 6.5 %

Chlorophyll : 0.34-0.55 %

Ash : 10.0 %

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Classification (Taxonomy)

� Class : Pteridophyta

� Order : Salvinales

� Family : Azollaceae/Salvinaceae

� Genus : Azolla

� Sub Genus : Eu-Azolla

Common Names:Azolla, water velvet, mosquito fern

Different species of Different species of AzollaAzolla

A. caroliniana A. Pinnata (SE Asia)

A. mexicana A. japonica

A. Microphylla A. filiculoides

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Azolla Caroliniana, is identified as a cold tolerant species

and survives well even at very low winter temperature of 5ºC during the months of December to February in mid

hills of Meghalaya.

Azolla pinnata, is a local isolate found widely in the entire

North Eastern Region, but does not survive under mid hills of Meghalaya.

However, Azolla caroliniana, has shown its adaptability in hills and other similar locations.

Adaptability

� Azolla caroliniana, can be preserved in shallow pond having 15 cm of standing water and by providing shade 10-15 cm above the pond water surface through weeds or paddy straw.

� For raising Azolla inoculum a pond size of 3 m x 2 m x 1 m is most desirable.

� Under such weed or straw mulch cover, the Azollamultiplies rapidly and inoculum will be ready within a period of 20-25 days for further releasing in the main multiplication ponds on the onset of monsoon in the month of April-May.

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How to grow Azolla?

� Azolla can easily be cultivated separately for periodic application in fish ponds.

� The system of cultivation involves a network of earthen raceways(20X3.0X0.6m) with water supply and drainage facilities.

� In each raceways, 6 kg of Azolla is incorpoprated. 65grams of single super phosphate is added.

� Water depth of 10-15 cm to be maintained. Azolla is harvested @25kg/raceway.

� It has been estimated that about 1 ton of Azolla can be harvested every week from a water area 650 m2

� It has also been reported that application of Azolla @ 20 tons/ha gives 50kg N, 13kg P, 45kg K.

How Azolla fixes atmospheric nitrogen?

� The remarkable feature of Azolla is that its symbiotic relationship with Cyanobacterium (Anabaena azollae) which remained on the dorsal leaf cavity of Azolla.

� The fern provides protein substances to Anabaena (BGA).

� The BGA then absorbed the atmospheric nitrogen and decomposes it through enzymic activity and converted in to soluble ammonia (NH4

+). It can fix 3-7 kg N/ha daily.

� It contains 4 % N on a dry-weight basis and is an excellent source of nitrogen fertilizer

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Favourable condition for higher

efficacy of Azolla

1. Water

2. pH

3. Salinity

4. Light & Shade

5. Herbicide level

6. Nutrition

WaterWater

�� AzollaAzolla must grow in water or wet mud to survive. It dies in a few must grow in water or wet mud to survive. It dies in a few hours if it becomes dry. Water control is critical, especially fhours if it becomes dry. Water control is critical, especially for year or year round production. A water level which allows the roots to touch round production. A water level which allows the roots to touch the the soil surface will often cause mineral deficiencies to appear. soil surface will often cause mineral deficiencies to appear.

� 10-15 cm fresh current water is necessary in multiplication pond.

Temperature: the day/night temperatures ranging between 32ºC and 20ºC have found to be most favorable. The optimum temperature for luxurious growth of Azolla is 25-30ºC.

�� Wind and wave action can eventually fragment and kill Wind and wave action can eventually fragment and kill azollaazolla. . Maintaining low water levels and rough plowing can protect Maintaining low water levels and rough plowing can protect azollaazollafrom wind. In Africa, hedges, bunds, and mixed culture (with crofrom wind. In Africa, hedges, bunds, and mixed culture (with crop p plants) are used to prevent wind damage. (Von Hove plants) are used to prevent wind damage. (Von Hove et alet al., 1983).., 1983).

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pH

Soil pH:

Azolla grows well in slightly acidic soil having pH 5.2 to 5.8.

Water pH: Water pH:

�� Since Since azollaazolla lives in water the following refers to the pH of the water onlylives in water the following refers to the pH of the water only. . AzollaAzolla can survive within a pH range of 3.5 to 10, but optimum growth can survive within a pH range of 3.5 to 10, but optimum growth is in the is in the range of 5 to 7. range of 5 to 7.

�� The relative growth rate is influenced by a direct relationship The relative growth rate is influenced by a direct relationship between light between light intensity and pH with the highest growth rates achieved at high intensity and pH with the highest growth rates achieved at high pH (9pH (9--10) and 10) and high light intensity and low pH (5high light intensity and low pH (5--6) and low light. 6) and low light.

�� Nitrogen fixation is optimal at pH 6 and 20Nitrogen fixation is optimal at pH 6 and 2000CC..

�� Deficiency problems can be caused in neutral to alkaline water bDeficiency problems can be caused in neutral to alkaline water because ferric ecause ferric ions precipitate. ions precipitate.

�� There can also be competition between ferrous and There can also be competition between ferrous and manganousmanganous ions in water ions in water with a neutral pH and reduction in absorption of both iron and with a neutral pH and reduction in absorption of both iron and managanesemanaganese with with high calcium concentrations. high calcium concentrations.

�� At pH 4, ferric ions are so readily available that a high concenAt pH 4, ferric ions are so readily available that a high concentration of calcium tration of calcium is required to balance the increased absorption of is required to balance the increased absorption of iorniorn, otherwise , otherwise azollaazolla suffers suffers from iron toxicity. (Lumpkin and from iron toxicity. (Lumpkin and PlucknettPlucknett, 1980)., 1980).

Salinity ToleranceSalinity Tolerance

�� The growth rate of The growth rate of azollaazolla gradually declines as salinity gradually declines as salinity increases. increases.

�� At about 1.3% salt (33% of sea water) the growth of At about 1.3% salt (33% of sea water) the growth of azollaazolla stops and higher concentrations will kill it. stops and higher concentrations will kill it.

�� In rice fields where salt concentration reaches 1480In rice fields where salt concentration reaches 1480--1872 mg/l during the dry season 1872 mg/l during the dry season azollaazolla wilts. wilts.

�� Salinity is a factor which should be looked wherever Salinity is a factor which should be looked wherever azollaazolla is being considered is being considered (Lumpkin and (Lumpkin and PlucknettPlucknett, 1980)., 1980).

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Shade Tolerance &Shade Tolerance & Herbicide SensitivityHerbicide Sensitivity

Shade Tolerance:Shade Tolerance:

Azolla prefers to grow well under partial shade. As dual cropping Azollagets partial shade from rice plant and therefore as dual cropping with rice is most successful.

�� Relative growth and Relative growth and nitrogenasenitrogenase activity is at a maximum at 50% of full activity is at a maximum at 50% of full sunlight although the difference between growth at 50% and 100% sunlight although the difference between growth at 50% and 100% sunlight is not that great. sunlight is not that great.

�� Heavy shading is known to decrease Heavy shading is known to decrease azollaazolla growth to almost zero growth to almost zero (Lumpkin and (Lumpkin and PlucknettPlucknett, 1980)., 1980).

Herbicide Sensitivity:Herbicide Sensitivity:

�� Most rice herbicides kill or inhibit Most rice herbicides kill or inhibit azollaazolla growth. Differences in growth. Differences in sensitivity are specific to the different sensitivity are specific to the different azollaazolla species (Moody and species (Moody and JaniyaJaniya, 1992)., 1992).

Being an N fixing fern Azolla does not require nitrogenous fertilizer for its growth.

Phosphorus is the most common limiting factor in the growth of azolla. Fronds placed in P deficient solution decrease or stop growth, become red, and develop curled roots. The minimum P requirement is not known but it thrives on as little as 1.1 mg P/liter.

Problems due to iron deficiency or toxicity are fairly frequent. Azolla fronds turn yellow when iron is lacking. Rapid growth is achieved with 1 ppm iron.

� Yield: Azolla produces around 300 tons of green biomaas/ha/year under normal sub tropical climate which is comparable to 800 kg of N (1800 kg of urea).

Nutrition

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Contribution of Azolla

�Basal application on green Azolla manure @ 10-12 t/ha

increases soil nitrogen by 50-60 kg/ha and reduces 30-35 kg

of nitrogenous fertilizer requirement of rice crop.

� Release of green Azolla twice as dual cropping in rice crop

@ 500 kg/ha enriches soil nitrogen by 50 kg/ha and reduces

N requirement by 20-30 kg/ha.

�Use of Azolla increases rice yield by 20 to 30 %.

�Rice varieties like DR-92, RCPL-1-87-8, Mendri, H-2850 and

Manipuri produced more than 30 q/ha rice when grown

with Azolla as dual cropping under natural soil fertility.

�Under low land condition a thick Azolla mat does

not allow the weeds to grow in rice filed thus, Azolla

suppresses the weed growth and creates congenial

condition for rice production.

Azolla reduces evaporation from water surface and

increases water use efficiency in rice.

Dry Azolla flakes can be used as poultry feed and

green Azolla is also a good feed for fishes.

Azolla is used in carp ponds at @ 40 ton/ha/yr

proving the full complement of nutrients.

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Ridged-field rice-azolla-fish model

� This design was originally developed for swampy areas with the objectives of improving soil properties and increasing rice yield. Later it was, stepwise, integrated with azolla and fish.

� Rice is planted on the ridge, azolla as a feed for fish as well as a biofertilizer, and green manure and fish are stocked in the trenches (Pl. seethe diagram in the next slide).

� In tropical Asia azolla is traditionally cultivated as a green manure for rice in two ways.

� One way is to set aside 5-10% of the crop area for year-round production. The cultivated azolla is later added to crop fields as compost.

� In the second way, azolla is cultivated in the rice fields and incorporated before and/or after the rice crop and between crops. Ideally azolla is grown several times before rice transplanting.

SourceSource

Li Li KangminKangmin (1992).(1992). Rice-fish farming in China: past, present and future, p.

17-26. In C.R. de la Cruz, C. Lightfoot, B.A. Costa-Pierce, V.R. Carangal and

M.P. Bimbao (eds.) Rice fish research and development in Asia. ICLARM

Conf. Proc. 24, 457 p.

Rice ridge and fish ditch farming system in ChinaRice ridge and fish ditch farming system in China

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2. Phosphatase activity with reference to bacteria

and phosphorus in tropical freshwater

aquaculture pond systems

�The bio-geochemical cycle of phosphorus is significantly influenced

by microbes in the aquatic environment.

�Phosphorus compounds are decomposed and mineralized by

enzymatic complexes such as phosphatases produced by microbes.

�Enzymatic catalysis results in the production of orthophosphate,which can be used readily by primary producers.

�Even the smallest concentration of phosphate in water has an

influence over the production process in aquaculture systems.

Phosphatase activity…

�Extracellular alkaline phosphatase activity was

observed in water and sediment media of

aquaculture ponds with different management

practices.

�Heterotrophic bacterial populations as well as

phosphatase-producing bacterial populations

were higher in sediments compared with water.

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Phosphatase activity…

� In the freshwater fish ponds, Bacillus spp. were the dominant forms of bacteria producing phosphatase.

� The alkaline phosphatase activity of sediment was always higher than that of water.

� The partitioning of extracellular alkaline phosphatase in pond water by a 0.22-µm membrane filter revealed that a proportion was often free rather than cell associated and might have originated as free enzymes released by enriched sediments or by fish or microbes.

Phosphatase activity…

�In the case of water, although the dissolved alkaline phosphatase activity was lower than the total alkaline phosphatase activity, the former was nevertheless unimportant, as it constitute about 20% of the 'total' activity.

�Free alkaline phosphatase activity shared a negative correlation with the orthophosphate concentration of water, whereas gross alkaline phosphatase activity was positively correlated with the total phosphorus and bacterial population of water.

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Seventeen rhizobacteria isolated from different ecological

regions, i.e. Brazil, Indonesia, Mongolia and Pakistan were

studied to develop inoculants for wheat, maize and rice.

Almost all the bacterial isolates were Gram ‘-’ve, fast-

growing motile rods and utilized a wide range of carbon

sources.

These isolates produced indole-3-acetic acid at

concentrations ranging from 0.8-42.1 µg/mL, irrespective of

the region.

Isolate 8N-4 from Mongolia produced the highest amount of

indole-3-acetic acid (42.1 µg/mL), produced siderophores

(0.3 mg/mL) and was the only isolate that solubilize

phosphate (188.7 µg P/mL).

o Nostoc, Calothrix, Gloeotrichia, Stigonema, etc are free-living

aerobically nitrogen fixing Cyanobacteria.

o In addition, Vesicular Arbuscular Mycorhizae (VAM fungi) are

free-living soil forms that increase nutrient uptake (specially by

converting organic phosphorus into inorganic phosphorus), plant

growth, nodulation and nitrogen fixation in legumes.

o Rhizobium producing root nodules in legumes and Anabaena

azollae living in leaf cavities of Azolla (aquatic fern) are very

efficient nitrogen fixers, and contribute about 500 kg N/ha/year.

3. Nitrogen fixing cyanobacteria

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Nitrogen fixing cyanobacteria…

Technology for production of BGA biofertiliser with simple nutrient medium in polyhouse has been standardized.

A thick mat was found to develop within 5 days.

A suitable carrier material has been developed where survival percentage of BGA strains was 85% even after two and half years of storage.

The carrier material, Montmorillonite Clay has been found to be very promising for BGA biofertilizers where it is essential to store the inoculums for a longer period.

Technology for large scale production of BGA inoculumbiofertilizers in Flexi bioreactors was developed at MaduraiKamraj University, Tamilnadu.

� Azotobacter species are free-living (mostly root associated),

aerobically nitrogen fixing bacteria.

� Rhizobium producing root nodules in legumes and thereby fix

nitrogen.

4. Nitrogen fixing bacteria

5. Enriched compost

� They are used in cellulolytic fungal culture -Phosphotika

and Azotobacter culture.

� In fish culture they not yet reported.