Post on 23-Dec-2020
E- Content M.Sc Semester II MBOTCC-5: Biofertilizer Technology, Unit 1
Name of Faculty: Dr Tanuja, University Department of Botany, Patliputra University
Topic: Introduction to biofertilizers
The term “Biofertilizer” or more appropriately “Microbial inoculants” can generally be
defined as preparation containing live or latent cells of efficient strains of nitrogen fixing,
phosphate solubilizing or cellulolytic microorganism used for application to seeds, soils or
composting areas with the objective of increasing the number of such microorganisms and
accelerate those microbial process which augment the availability of nutrients that can be
easily assimilated by plants.
Biofertilizers, being biological in origin are considred to be relatively safe and sustainable.
They are capable of supplying not only major nutrients but also micronutrients for effective
growth of plants. Most of the biofertilizers are produced through involvement of
microorganisms.
Since biofertilizers can successfully be used in many variety of crops grown under different
agro-ecologies, their potential requirement is quite large and is reported to far exceed the
present production levels. It is assumed that biofertilizers can substitute about 25% of the
nutrient requirement of the crops. Nitrogen is a key component of nutrients for plants.
Inputs of biologically fixed Nitrogen into agricultural systems are derived from symbiotic
relationship between legume and Rhizobium, as well as due to non-symbiotic association
between free living diazotophs and plant roots.
Biofertilizer improves soil particles and sustain soil fertility. It has been reported that the
benefit to cost ratio of biofertilizer is fairly high. Some authors have reported that
biofertilizers harness atmospheric nitrogen and make it available directly to the plant.
According to Subba Rao, 1993,it helps in increasing phosphorous uptake and releasing
unavailable phosphorous. It enhances root proliferation due to release of growth promoting
hormones .
Benefits of Biofertilizers
It helps in maintaining environmental health by reducing the level of pollution.
Reduces human & animal hazards by reducing the level of residue in the product.
Increases the agricultural products and makes it sustainable
Ensures the optimum utilization of natural resources.
Reduces the risk of crop failure.
Improves the physical and chemical properties of soil
Biofertilizers are cost-effective when compared to synthetic fertilizers
Using biofertilizers can increase crop yield by 20 or 30 percent.
Drawbacks of Biofertilizers
Slow-release
Crop specific
Strain-specific
Soil specific—lose effectiveness if soil too dry or hot
Lesser efficient than synthetic fertilizers
Crops show less response to biofertilizers then chemical fertilizers
Much lower nutrient density — requires large amounts to get enough for most crops.
HISTORICAL DEVELOPMENT OF BIOFERTILIZERS
Inoculation of plants with beneficial bacteria can be traced back to centuries. Although
bacteria were not proven to exist until Von Leeuwenhoek in 1683 discovered microscopic
‘animals’, their utilization to stimulate plant growth 3 in agriculture has been exploited since
ancient times. Theophrastus (372-287 BC) suggested the mixing of different soils as a means
of remedying defects and adding heart to the soil . From experience farmers knew that
when they mixed soil, taken from previous legume crop with soil in which non-legumes
were to be grown, yields often improved. By the end of the 19th century, the practice of
mixing “naturally inoculated” soil with seeds became a recommended method of legume
inoculation in the U.S.A. A decade later, the first patent (“Nitragin”) was registered for plant
inoculation with Rhizobium sp. Eventually the practice of legume inoculation with non-
symbiotic, associative rhizosphere bacteria, like Azotobacter, was used on a large scale in
Russia in 1930s and 1940s. Bacillus megaterium for phosphate solublization was used in the
1930s on large scale in Eastern Europe.
In India, from 1920 onwards Joshi Desai, Vyas, Biswas and Acharya worked on phosphate
requirements of legumes for better recuperation of soil nitrogen and on anaerobic digestion
of organic matter at Imperial Agricultural Research Institute. At the same time, Madhok
introduced the practice of using bacterial cultures for beerseem (Trifolium alexandrium) in
Punjab. Sanyasi Raju and Rajagopalan worked on root nodulation of Bengal gram and
groundnut at the Madras Agricultural College, Coimbatore (Subbarao, 1977).
The production of rhizobial inoculants was first undertaken at IARI, New Delhi in 1956
although its commercialization started in late 1960s when soybean was introduced for the
first time in the country. Inoculants for pulses, oilseeds and fodder legumes were also
produced. The processes of development of rhizobial inoculants for various 4 legumes in
India has made considerable progress following the field evaluation of the inoculants on
yields of various pulses, soybean, groundnut and fodder legumes was carried under the All
India Coordinated Research Programmes of the respective crops by the Indian Council of
Agricultural Research, New Delhi. The use of inoculants has considerably increased over the
years and a number of private producers have come into operation. It is therefore,
imperative to control the quality of inoculants.
Accordingly, the Bureau of Indian Standards has sprung into action and specific standards
for Rhizobium, Azotobacter, Azospirillum and phosphate solublizing bacterial inoculants
have been brought out. Some of the nitrogen fixers colonize the root zones and fix nitrogen
in loose association with plants. A very important bacterium of this category is Azospirillum
which was discovered by Brazilian scientist, J. Dobereiner. In the late 1970s Azospirillum was
found to enhance non-legume plant growth. In recent years, various other rhizobacteria
such as Aeromonas veronii, Azotobacter sp., Azoarus sp, Cyanobacteria (predominantly of
the genera Anabaena and Nostoc) Alcaligenas, Burkholderia, Comamonas acidororans,
Enterobacter, Erwinia, Flavobacterium, rhizobia (including the Allorhizobium, Azorhizobium,
Bradyrhizoblum, Mesorhizobium, Rhizobium and Sinorhizobium) Gluconacetobacter
diazotrophicus, Herbaspirillum seroepdicae, Serratia, Variovorax paradoxus and
Xanthomonas maltophilia have been identified for their use either as biofertilizers or
biological control agents (Bioinoculants).
TYPES OF BIOFERTILIZERS :There are various types of biofertilizers which are as follows:
(a) Nitrogen-fixing biofertilizers:
(i) Symbiotic nitrogen fixers - Rhizobium
(ii) Non-symbiotic nitrogen fixers
- Azotobacter
- Azospirillum
- Blue green algae (Nostoc,Anabaena etc)
– Azolla
(b) Phosphorous mobilizing biofertilizers:
(i) Phosphate solublizer
- Bacillus
- Pseudomonas
- Aspergillus niger
(ii) Phosphate absorber
- VAM fungi (eg) Glomus, Gigaspora
(c) Organic matter decomposer biofertilizers
(i) Cellylolytic
- Cellulomonus
- Trichoderma
(ii) Lignolytic
- Arthrobacter
- Agaricus
Some images of biofertilizers:
Anabaena azollae Nostoc
Azolla Azotobacter(petri plate) After Gram Staining
Root nodule Rhizobium streaked on petriplate After Gram staining
Cellulomonas (on petri plate) Different isolated spores of VAM