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8/3/2019 Bnf Presentation

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GROUP:2

M.PHIL BOTANY

1ST SEMESTER


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Muhammad Shoaib Amjad Humaira Amin

Parveen Akhtar Shadana


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COURSE CODE: BIOL-735TOPIC: BIOLOGICAL

NITROGENFIXATION,PERSPECTIVES

AND LIMITATION


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DEFINITION

Biological nitrogen fixationis the process whereatmospheric nitrogen isreduced to amonia in thepresence of nitrogenaseenzyme with the help of

microorganisms


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Biological Nitrogen Fixation and SustainableAgriculture

Nitrogen fixing micro-organisms could be an importantcomponent of sustainable agricultural systems.

There are several significant reasons to seek alternativesto fertilisers that provide

chemically fixed nitrogen:

Environmental

EnergySustainability

Nutrition


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Environmental

Nitrogen fertilisers affect the balanceof the global nitrogen cycle, and may

pollute groundwater, increase the riskof chemical spills, and increaseatmospheric nitrous oxide (N2O), a

potent greenhouse gas.


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Energy

The primary energy source for themanufacture of nitrogen fertiliser is

natural gas together with petroleumand coal. On the contrary, the energyrequirements of BNF are met by

renewable sources such as plant-synthesised carbohydrates ratherthan from nonrenewable fossil fuels.


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Sustainability

Long- term sustainability of agriculturalsystems must rely on the use and

effective management of internalresources. The process of BNF offers aneconomically attractive and ecologically

sound means of reducing externalnitrogen input and improving the qualityand quantity of internal resources.


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Nutrition

It is estimated that about 20% of foodprotein worldwide is derived from

legumes. There are more than 13,000described species of legumes and for only3,000 species examined more than 90%were found to form root nodules. Because

few have been exploited for food, there isthe prospect that the utilisation oflegumes could be expanded substantially.


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Conti.

It is anticipated that increasingdemographic pressure and fooddemand will require theexploitation of BNF as a major

source nitrogen for plant proteinproduction.


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Factors, affecting BNF:Management decisions

Environmental factors affecting nitrogen fixation include:

Temperature

Moisture

acidity

several chemical components of the soil such asnitrogen, phosphorus, calcium and molybdenum content


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Conti..

It is often difficult to isolate the effect of theabove factors on inoculation success from theirinfluence on symbiosis and nitrogen fixation.

For example:acidity, as well as, calcium, aluminium and

manganese concentrations will interact andaffect both bacterial proliferation, root-hairinfection and plant growth.


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Conti.

In addition to the competitiveness of the

rhizobia in forming nodules and theeffectiveness of the rhizobium-host plantto fix N2, a series of edaphic, chemical

and biophysical factors exert a control onN2 fixation.


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Management practices like the intensity of tillageor intercropping practices will alter thoseedaphic, chemical and biophysical factors andtherefore influence BNF indirectly are:

Temperature & moistureEffect:

survival, of rhizobia in soil abilities to nodulate and fix nitrogen inhibition of nitrogen fixation


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Recommendations

Placement of inoculum in deeper soillayers when top soil temperature are high

The surface mulches may conservemoisture and reduce soil temperature


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Nitrogen FertilisationEffect:Generally combined N delays or inhibits

nodulation and nitrogen fixation. Because of thisadverse effect, N fertilisation usually is notrecommended for leguminous crops.

However there may be situations where N has to

be applied, such as to cereals in mixed croppingor rotations and then fertiliser may affectnitrogen fixation of the legume crop.


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Recommendations

The development of grain legumes which areless sensitive to mineral N should not be

pursued unless there is increase in N-uptake andan improvement in the overall use efficiency ofavailable N.

It is possible to apply small amounts of soil orfoliar N fertiliser, which may increase yieldwithout reducing the amount of nitrogen fixed.


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Pesticides, fungicides andinsecticides

Effects:

The compatibility of rhizobia with pesticides ispoorly understood except for Fungicides.

Insecticides have little adverse effect onnodulation when not directly applied on seed.

The effect of herbicides on rhizobial survival isunknown.


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Recommendations

Due to the variability of the effect it isrecommended to test the particularRhizobium inoculum and its behaviour in

respect to the product to be used, beforeapplication

The effect of pesticide on N fixationshould be minimised by separateplacement of rhizobia and pesticide


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Acid soils

Effects:

Acid soils constrain agricultural production and nitrogenfixation.

Recommendations:

Use of acid-tolerant legume cultivars and rhizobium

Soil liming should be limited to achieving a pH at whichavailable aluminium or manganese levels are no longertoxic.


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Tillage

Effects:

When tillage is minimised, lower rates of

mineralization and nitrification, coupledwith increased N immobilisation and ahigher potential for denitrification will lead

to a decrease in available N.


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Recommendations

Limiting tillage can stimulate N demandand N2 fixation.

Conservation and zero tillagemanagement practices will, therefore, leadto a stimulation of N2 fixation, at least

until a new equilibrium between residueinput and the rate of decomposition isreached.


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