This document provides information on biofertilizers. It discusses that biofertilizers are nutrient inputs of biological origin that aid plant growth through microbiological processes. Important microorganisms used as biofertilizers include nitrogen-fixing bacteria, fungi, cyanobacteria, and ferns. These microorganisms can fix nitrogen either symbiotically, by forming relationships with plants, or non-symbiotically as free-living organisms. The document also describes methods for mass cultivating and applying different types of biofertilizer microorganisms, such as Rhizobium bacteria and blue-green algae, to benefit agricultural crops.

1. BIOFERTILIZER

2. Introduction
 The term biofertilizer denotes the ‘nutrient inputs of biological origin for
plant growth.
 Here biological origin should be referred to as microbiological process
synthesizing complex compounds and their further release into outer medium,
to the close vicinity of plant roots which are again taken up by plants.
 Nitrogen compounds account for 40-50% of the dry matter of protoplasm of
plant cells.
 Development and use of biofertilizers is mainly concerned with the
exploitation of a group of nitrogen fixing organisms called diazotrophs for
harvesting atmospheric nitrogen for plant crops.
 This microbial process of producing the inorganic forms of nitrogen from
molecular nitrogen is known as nitrogen fixation or diazotrophy.

3. Micro-organisms have potential
applications as Biofertilizer are:-
 Bacteria: Rhizobium sp, Azospirillum, Azotobacter
 Fungi: Mycorrhiza
 Blu-green algae (cyanobacteria): Anabena, Nostoc
 Fern: Azolla (containing a symbiont Anabena azollae)

4.  The diazotrophs exhibit two modes of nitrogen fixation, viz.,
(i) non-symbiotic and
(ii) symbiotic.
 Those microorganisms(mos) that pass independent life and fix atmospheric
nitrogen are known as free-living diazotrophs or non-symbiotic mos.
 those mos which establish symbiotic relationships with plants for fixing
nitrogen are called symbiotic diazotrophs.
 The plants and the symbiotic diazotroph exhibit mutualism whereby the plant
exchanges carbohydrates (energy source) with the diazotroph for the nitrogen
the latter fixes.

5. Species of Rhizobium and cross
inoculation groups of hosts
Legume category/group Rhizobium species
Soybeans Rhizobium japonicum
Peas and vetch Rhizobium leguminosarum
Beans Rhizobium phaseoli
Lupines Rhizobium lupini
Cowpeas Rhizobium sp
Alfalfa Rhizobium meliloti
Clover Rhizobium trifoli

6.  Before rhizobia can fix nitrogen, they must establish themselves in the cells of
the root tissue of the host plant.
 The bacteria invade the host plant cells via this infection thread, causing
enlargement and an increased rate of cell division.
 This event leads to the formation of abnormal growth (nodule formation) in the
root system.
 Within the nodules the bacteria convert free nitrogen to nitrates, which the host
plant utilizes for its development.

8. Production of Rhizobium culture
 Bacteria to be inoculated in soil as Biofertilizer need to be multiplied on
artificial media to harvest on a large scale so that it can be supplied to
farmers.
 Strains of Rhizobium are grown in Yeast Extract Mannitol (YEM) broth, the
composition of which is:
Yeast extract 1g
Mannitol 10g
K2HPO4 0.5g
MgSO4.7H2O 0.2g
NaCl 0.1g
Distilled water 1000ml
pH 6.5-7.0

9. The principal steps for mass cultivation are:
 Sterilize the growth medium and inoculate with broth of mother culture
prepared in advance.
 Incubate for 3-4 days at 30-32°C.
 Test the culture for its purity and transfer to a large fermentor equipped with
temperature control and aeration device. Allow aerobic fermentation for 4-9
days. There should be profuse growth of bacteria.
 Check the quality of the broth.
 Blend the broth with sterile carrier, e.g., peat, lignite, farmyard manure and
charcoal powder. The carrier should contain 1×109 to 4×109 rhizobial cells per
gram.
 Pack the culture in polyethylene bags and store at 4°C or supply to the
farmer.

10. Application of rhizobial culture at the
farm level
 There are variations in the method of application of Rhizobial culture at the farm
level. One very successful method entails seed inoculation with aqueous
suspension of carrier culture during sowing.
 The method of preparing seed inoculant is as follows:
1. Prepare 10% sugar or Jaggery solution by boiling in water and then cool.
2. Add Gum Arabic (10%) to help Rhizobial cells stick to the seed.
3. Add the carrier based Rhizobial culture to the solution and mix well. For one
hectare, 400g of charcoal based culture would be sufficient.
4. Add seeds in the slurry and again mix well. The no. of Rhizobial cells per seed
should be between 105 and 106.
5. Spread the seeds in shade for drying.
6. Store the seeds at 4°C or use them in the farm.

12. Production of blue-green algae
 The process of application of blue-green algal culture in field as biofertilizer
is also called algalization.
 The biofertilizer is beneficial for paddy. The mass cultivation of
cyanobacterial fertilizers is done in various ways, viz.,
 Cemented tank method
 Shallow metal trough method
 Polyethylene lined pit method
 Field method

13. Mass cultivation of cyanobacteria is done by
using any of the four methods under the
following steps:
 Prepare the cemented tanks, shallow trays of iron sheets or polyethylene-lined pits in an
open area. Width of tanks or pits should not be more than 1.5m. This will facilitate the
proper handling of culture
 Transfer 2-3kg soil (collected from open place for 1m2 area of tank) and add 100g of
super-phosphate. Water the pit to about 10cm height. Mix lime to adjust to pH 7.0. Add
2ml of insecticide, e.g., malathion to protect the culture from mosquitoes. Mix well and
allow soil particles to settle down
 When the water becomes clear, sprinkle 100g of starter inoculum on the surface of water
 When temperature remains between 35 and 40°C during the summer, optimum growth of
cyanobacteria is achieved. Always maintain the water level to about 10cm during this
period
 After drying, the algal mat will get separated from the soil and form flakes. During
summer, about 1kg pure algal mat/m2 area is produced. These are collected, powdered,
kept in sealed polyethylene bags and supplied to the farmers

14. Thank You