This document discusses various types of biofertilizers that can be used to promote plant growth and increase soil fertility in a sustainable way. It describes how biofertilizers like nitrogen-fixing bacteria, mycorrhizal fungi, blue-green algae, and the fern Azolla can fix atmospheric nitrogen in the soil to increase nutrient availability for plants. Green manure crops are also considered a type of biofertilizer, as they improve soil structure and organic matter content when plowed under. The document emphasizes that an integrated approach using both chemical fertilizers and biofertilizers is best for sustainable agriculture.

1. Biofertilizers:
Introduction:
A Bio fertilizer is a substance which contains living microorganisms which, when applied to
seeds, 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. In fact, the Biofertilizers are microbial inoculants or carrier based preparations
containing living or latent cells of efficient strains of nitrogen fixing, phosphate is solublizing
and cellulose decomposing microorganisms intended for seed or soil application and
designed to improve soil fertility and plant growth by increasing the number and biological
activity of beneficial microorganisms in the soil.
The objects behind the application of Biofertilizers or microbial inoculants to seed, soil or
compost pit is to increase the number and metabolic activity of useful microorganisms that
accelerate certain microbial processes to augment the extent of availability of nutrients in
the available forms which can be easily assimilated by plants. The need for the use of
Biofertilizers has arisen primarily due to two reasons i.e. though chemical fertilizers increase
soil fertility, crop productivity and production, but increased use of chemical fertilizers has
caused serious concern of soil texture, soil fertility and other environmental problems, use
of Biofertilizers is both economical as well as environment friendly. Therefore, an integrated
approach of applying both chemical fertilizers and Biofertilizers is the best way of integrated
nutrient supply in agriculture.
Organic fertilizers are also considered as Biofertilizers, which are rendered in available forms
due to the interactions of microorganisms or their association with plants.
Biofertilizers, thus include:
i) Symbiotic nitrogen fixers Rhizobium sp.
ii) Non-symbiotic, free living nitrogen fixers Azotobacter, Azospirillum etc.
iii) BGA-inoculantsAzolla-Anabaena,
iv) Phosphate solubilizing microorganisms (PSM) Bacillus Pseudomonas, Penicillium
Aspergillus etc.
v) Mycorrhiza.
vi) Cellulolytic microorganisms.
vii) Organic fertilizers.
1. Bacteria as Biofertilizers:
Many free living and symbiotic bacteria fix nitrogen in the soil. Increase of such bacteria may
increase the gross yield of nitrogen.

2. There are two methods applied for it:
Bacterization
Bacterization usually means treatment of seeds or seedling roots with. cultures of bacteria
that will improve plant growth; such preparations are frequently. called bacterial fertilizers.
It is a technique of seed dressing with bacteria.
Example: Azotobacter,bacillus,rhizhobium,etc
Green manuring:
Green manuring is the plowing under or soil incorporation of any green manure crops while
they are green or soon after they flower. Green manures are forage or leguminous crops
that are grown for their leafy materials needed for soil conservation.
Azotobakterin:
It contains cells of Azetobacter, Chroococcum.
Rhizobium:
Rhizobium are able to enter into symbiotic relationship with legumes they fix atm. nitrogen
and thus not only increase the production of the inoculated crops but leave a fair amount of
nitrogen in the soil, which benefit the subsequent crops. Psedomonas fouresence and
P.putida are imp phosphate solubilizing bacterial fertilizers they convert non-available
inorganic phosphates into soluble phosphates, which can be utilized by crop plants.
2. Mycorrhiza as Biofertilizers:
Mycorrhiza is a symbiotic association of fungi with the roots of plants so that the nutrients
absorbed from the soil by the fungus are released to the host cells and in turn the fungus
takes its food requirements from the soil
Mycorrhiza having two types
- Ectomycorrhiza
- Endomycorrhiza
Ectomycorrhiza:
Ectomycorrhiza are found on the roots of forest trees, they absorb nitrogen, phosphorus,
potassium and calcium. They also convert complex organic molecules into simpler available
forms, protects the roots from the pathogens and produce cytokinin.
Endomycorrhiza:
These Are found on the roots of most fruit and other horticultural crops, e.g coffee, pepper.
They particularly help in phosphorus nutrition. They also produce growth promoting
substances and offer resistance against pathogens. The seedlings are treated with

3. endomycorrhiza and transplanted in the field as done by citrus growers. Fungus strains of
azotobacter, aspergillus are used as endomycorrhiza.
3. Algae as Biofertilizers:
The role of blue green algae was 1st realized by Singh in 1961 while studying the paddy field.
Most widely used class of algae as biofertilizers are Blue green algae.
Algalization:
It is the process of application of blue green algal culture in the field as biofertilizers. A layer
of blue green algae growing on water surface is scrapped, dried, powdered and stored in
bags for supply to farmers. Algal cultures are applied after 10 days of rice transplantation.
Nitrogen Fixation:
These blue green algae
1. Multiply
2. Fix atmospheric Nitrogen
3. Release it.
They release the fixed nitrogen in form of amino acids, proteins and certain growth
promoting substances.
Other Advantages:
This algal biomass is used as organic matter.
The growth promoting substances promote growth of plant.
These provide tolerance to fungicides and pesticides.
They help in reclamation of salinity to soil.
Composite cultures:
This was first studied by Tyagi in 1991. Spirogyra provides organic matter that promotes
rice growth. The mucilaginous sheath of spirogyra has microorganisms that may fix
nitrogen. Composite culture of blue green algal genera is more effective than single generic
culture. Nostocand Aulosiraare strong nitrogenfxingbluegreenalage sotheygive highestbiomass
and yeild of rice. Nostoc effect alone intermediate. Higher than that of Spirogyra. Lower than
that of Aulosira.
Aulosira > Nostoc > Spirogyra.
4. Azzola as Bio fertilizer:
With the decrease in fossil reserves and increase in cost of commercial nitrogen fertilizers
something had to be done. Use of plant symbiotic systems combined with nitrogen fixation
is an alternative. Aquatic fern of the genus azolla presents a symbiotic association with the

4. Cyanobacterium, Anabaenna Azollae. The aquatic fern of the genus Azolla is a small-leaf
floating plant. It contains endosymbiotic community living in the leaf cavity
Theme:
One of the most interesting features is the role played by the cyanobacterium in this
association. Filaments of Anabaena azollae are localised in a cavity of the dorsal side of the
leaf. Here special conditions stimulate high heterocyst frequency and a vegetative cell
differentiation during leaf development. In mature leaves, the Anabaena filaments cease to
grow and differentiate heterocyst’s, which are the site of N2 fixation. This symbiotic
association is the only fern-cyanobacteria association that presents agricultural interest.
Conclusion:
As a result, Azolla-Anabaena can fix almost three times more atmospheric nitrogen than
legumes. Typical rates for legumes are 400 kg of nitrogen per hectare per year those for
Azolla-Anabaena are 1100 kg of nitrogen per hectare per year.
5. Green Manuring:
A growing crop, such as clover or grass, that is plowed under the soil to improve fertility is
often referred to as Green manure. Nitrogen and phosphorus are deficient in Pakistani soils
and there is hardly any soil from which high yields can be obtained without any fertilization.
The problem we face these days are:
- Energy Used for Fertilizer Production.
- Energy Crisis.
To counter both of these we can use green manuring as a matter of fact it does not utilizes
energy.
Types of Green Manuring:
Green Manuring In-situ:
When green manure crops are grown in the field itself either as a pure crop or as intercrop
with the main crop and buried in the same field, it is known as Green Manuring In-situ.
Green leaf Manuring:
It refers to turning into the soil green leaves and tender green twigs collected from shrubs
and trees grown on bunds, waste lands and nearby forest area.
Some Green Manuring Crops:
 Legumes
 cowpeas
 Soybeans
 sweet clover

5.  Vetch
 Millet
 sorghum
Characteristics of a Good Manure:
Short Period:
Yield a large quantity of green material within a short period.
Quick Growing:
Be quick growing especially in the beginning, so as to suppress weeds.
Nitrogen Fixation:
Preferably is a legume, so that atm. ‘N’ will be fixed.
Root System:
These have deep and fibrous root system so that it will absorb nutrients from lower zone
and add them to the surface soil and also improve soil structure.
Method of Green Manuring:
When the crop reach full bloom than With the help of sohaga fall all the green manure crop
in the field,Then mix the crop with the help of rotavator and disc harrow and give irrigation
to start the process of decomposition.
Fertility Improvement of Soil:
They absorb nutrients from the lower layer and leave them in surface when ploughed. They
prevent leaching of nutrients to lower layers. Harbour N fixing bacteria, rhizobia in root
nodules and fix atmospheric. N (60 to 100 kg N/ha).
Advantages of Green Manuring:
 They improve soil Structure.
 It has positive influence on the physical and chemical properties of soil.
 Provides organic Matter.
 Helps to maintain the organic matter status of soil.
 Source of Food and Energys.