Role of Biofertilizers in Agriculture

Abstract

Biofertilizers are natural fertilizes which are living microbial inoculants of bacteria, algae,
fungi alone or in combination and they augment the availability of nutrients to the plants. The
role of biofertilizers in agriculture assumes special significance, particularly in the present
context of increased cost of chemical fertilizer and their hazardous effects on soil health.

Full text

Popular
Article
Role of Biofertilizers in Agriculture
Rakesh Kumar
1
, Narendra Kumawat
2*
and Yogesh Kumar Sahu
3
1
Scientist (Agronomy), ICAR Research Complex for NEH Region, Nagaland Centre Jharnapani -797 106
2
AICRP Maize, Zonal Agricultural Research Station, Jhabua 457 661, MP
3
Krishi Vigyan Kendra, Jhabua 457 661, MP, India
*Email of corresponding author: kumawatandy@gmail.com
Introduction
Modern agriculture emphasizes in using hybrid seeds and high yielding varieties that are highly
responsive to large doses of chemical fertilizers and irrigation. Indiscriminate use of synthetic fertilizers
has led to pollution and contamination of soil and water basins. This has resulted in soil being deprived of
essential plant nutrients and organic matter. It has led to depletion of beneficial micro-organisms and
insects indirectly reducing soil fertility and making crops more prone to diseases. It is estimated that by
2020, to achieve the targeted production of 321 million tons of food grain, the requirement of nutrient will
be 28.8 million tons, while their availability will be only 21.6 million tons being a deficit of about 7.2
million tons, thus depleting feedstock/fossil fuels (energy crisis) and increasing cost of fertilizers which
would be unaffordable to small and marginal farmers, thus intensifying the depleting levels of soil fertility
due to widening gap between nutrient removal and supplies.
Chemical fertilizers which are now being used extensively since the green revolution have
depleted soil health by making the soil ecology non - inhabitable for soil micro flora and micro fauna
which are largely responsible for maintaining soil fertility and providing some essential and indispensable
nutrients to plants. Biofertilizers are the products containing one or more species of microorganisms which
have the ability to mobilize nutritionally important elements from non usable to usable form through
biological processes such as nitrogen fixation, phosphate solubilisation, excretion of plant growth
promoting substances or cellulose and biodegradation in soil, compost and other environments. In other
words, biofertilizers are natural fertilizes which are living microbial inoculants of bacteria, algae, fungi
alone or in combination and they augment the availability of nutrients to the plants. The role of
biofertilizers in agriculture assumes special significance, particularly in the present context of increased
cost of chemical fertilizer and their hazardous effects on soil health.
Biofertilizer: The Need of the Hour in Agriculture
At present times, there is a growing concern about environmental hazards and threats to sustainable
agriculture. In view of the above stated facts, the long term use of bio-fertilizers proves to be economical,
eco-friendly, more efficient, productive and accessible to marginal and small farmers over chemical
fertilizers. The need for the use of biofertilizer thus arises primarily for two reasons. First, because
increase in the use of fertilizers leads to increased crop productivity, second, because increased usage of
chemical fertilizer leads to damage in soil texture and raises other environmental problems.
Biofertilizers are natural fertilizes which are living microbial inoculants of bacteria, algae,
fungi alone or in combination and they augment the availability of nutrients to the plants. The
role of biofertilizers in agriculture assumes special significance, particularly in the present
context of increased cost of chemical fertilizer and their hazardous effects on soil health.
Popular Kheti
Volume -5, Issue-4 (October-December), 2017
Available online at www.popularkheti.info
© 2017 popularkheti.info
ISSN: 2321-0001
Popular Khet
i
ISSN: 2321
-
0001
63

Popular
Article
Classification of Biofertilizers
Several microorganisms and their association with crop plants are being exploited in the production of
biofertilizers. They can be grouped in different ways based on their nature and function.
Rhizobium: Rhizobium is a soil habitat bacterium, which colonizes legume roots and fixes atmospheric
nitrogen symbiotically. The morphology and physiology of Rhizobium vary from free-living condition to
the bacteroid of nodules. They are the most efficient biofertilizer as per the quantity of nitrogen fixed
concerned. They have seven genera and are highly specific to form nodule in legumes, referred as cross
inoculation group.
Azotobacter: Of the several species of Azotobacter, A. chroococcum happens to be the dominant
inhabitant in arable soils capable of fixing N2 (2-15 mg N2 fixed /g of carbon source) in culture media.
The bacterium produces abundant slime which helps in soil aggregation. The numbers of A. chroococcum
in Indian soils rarely exceeds 105/g soil due to lack of organic matter and the presence of antagonistic
microorganisms in soil.
Azospirillum: Azospirillum lipoferum and A. brasilense (Spirillum lipoferumin earlier literature) are
primary inhabitants of soil, the rhizosphere and intercellular spaces of root cortex of graminaceous plants.
They develop associative symbiotic relationship with graminaceous plants. Apart from nitrogen fixation,
growth promoting substance production (IAA), disease resistance and drought tolerance are some of the
additional benefits of inoculation with Azospirillum.
Cyanobacteria: Both free-living as well as symbiotic cyanobacteria (blue green algae) have been
harnessed in rice cultivation in India. Once so much publicized as a biofertilizer for rice crop, it has not
presently attracted the attention of rice growers all over India. The benefits due to algalization could be to
the extent of 20-30 kg N/ha under ideal conditions but the labour oriented methodology for the preparation
of BGA biofertilizer is in itself a limitation.
Azolla: Azolla is a free-floating water fern that floats in water and fixes atmospheric nitrogen in
association with nitrogen fixing blue green alga Anabaena azollae. Azolla either as an alternate nitrogen
sources or as a supplement to commercial nitrogen fertilizers. Azolla is used as biofertilizer for wetland
rice and it is known to contribute 40-60 kg N/ha per rice crop.
Phosphate solubilizing microorganisms (PSM): Several soil bacteria and fungi, notably species of
Pseudomonas, Bacillus, Penicillium, Aspergillusetc. secrete organic acids and lower the pH in their
vicinity to bring about dissolution of bound phosphates in soil. Increased yields of wheat and potato were
demonstrated due to inoculation of peat based cultures of Bacillus polymyxa and Pseudomonas striata.
AM fungi: The transfer of nutrients mainly phosphorus and also zinc and sulphur from the soil milleu to
the cells of the root cortex is mediated by intracellular obligate fungal endosymbionts of the genera
Glomus, Gigaspora, Acaulospora, Sclerocysts and Endogone which possess vesicles for storage of
nutrients and arbuscles for funnelling these nutrients into the root system. By far, the commonest genus
appears to be Glomus, which has several species distributed in soil.
Silicate solubilizing bacteria (SSB): Microorganisms are capable of degrading silicates and aluminium
silicates. During the metabolism of microbes several organic acids are produced and these have a dual role
in silicate weathering. They supply H+ ions to the medium and promote hydrolysis and the organic acids
like citric, oxalic acid, Keto acids and hydroxy carbolic acids which form complexes with cations,
promote their removal and retention in the medium in a dissolved state.
Plant growth promoting rhizobacteria (PGPR): The group of bacteria that colonize roots or rhizosphere
soil and beneficial to crops are referred to as plant growth promoting rhizobacteria (PGPR). The PGPR
inoculants promote growth through suppression of plant disease (termed Bioprotectants), improved
nutrient acquisition (termed Biofertilizers), or phytohormone production (termed Biostimulants). Species
of Pseudomonas and Bacillus can produce as yet not well characterized phytohormones or growth
regulators that cause crops to have greater amounts of fine roots which have the effect of increasing the
absorptive surface of plant roots for uptake of water and nutrients. These PGPR are referred to as
Biostimulants and the phytohormones they produce include indole-acetic acid, cytokinins, gibberellins and
inhibitors of ethylene production.
Popular Khet
i
ISSN: 2321
-
0001
6
4
Kumar et al., 2017, Pop. Kheti, 5(4): 63-66

Popular
Article
Types of Biofertilizers
S. No. Types of biofertilizers Examples
N
2
fixing Biofertilizers
1. Free-living Azotobacter, Beijerinkia, Clostridium, Klebsiella, Anabaena,
Nostoc
2. Symbiotic Rhizobium, Frankia, Anabaena azollae
3. Associative Symbiotic Azospirillum
P Solubilizing Biofertilizers
4. Bacteria Bacillus megaterium var. phosphaticum, Bacillus subtilis,
Bacillus circulans, Pseudomonas striata
5. Fungi Penicilliumsp, Aspergillus awamori
P Mobilizing Biofertilizers
6. Arbuscularmycorrhiza Glomussp., Gigaspora sp., Acaulospora sp.,
Scutellospora sp. & Sclerocystis sp.
7. Ectomycorrhiza Laccaria sp., Pisolithus sp., Boletus sp., Amanita sp.
8. Ericoid mycorrhizae Pezizellaericae
9. Orchid mycorrhiza Rhizoctonia solani
Biofertilizers for Micro nutrients
10. Silicate and Zinc
solubilizers Bacillus sp.
Plant Growth Promoting Rhizobacteria
11. Pseudomonas
Pseudomonas fluorescens
Methods of Application of Biofertilizers
Seed Treatment: 200 g of biofertilizer is suspended in 300- 400 mL of water and mixed gently with 10 kg
of seeds using an adhesive like gum acacia, jiggery solution, etc. The seeds are then spread on a clean
sheet/cloth under shade to dry and used immediately for sowing.
Seedling Root Dip: This method is used for transplanted crops. For rice crop, a bed is made in the field
and filled with water. Recommended biofertilizers are mixed in this water and the roots of seedlings are
dipped for 8-10 h and transplanted.
Soil Treatment: 4 kg each of the recommended biofertilizers is mixed in 200 kg of compost and kept
overnight. This mixture is incorporated in the soil at the time of sowing or planting.
Advantages of Using Biofertilizers
Some of the advantages associated with biofertilizers include:
• They are eco- friendly as well as cost effective
• Their use leads to soil enrichment and the quality of the soil improves with time.
• Though they do not show immediate results, but the results shown over time are spectacular.
• These fertilizers harness atmospheric nitrogen and make it directly available to the plants.
• They increase the phosphorous content of the soil by solubilising and releasing unavailable
phosphorous.
• Biofertilizers improve root proliferation due to the release of growth promoting hormones.
• Microorganism converts complex nutrients into simple nutrients for the availability of the plants.
• Biofertilizer contains microorganisms which promote the adequate supply of nutrients to the host plants
and ensure their proper development of growth and regulation in their physiology.
• They help in increasing the crop yield by 10-25%.
• Biofertilizers can also protect plants from soil born diseases to a certain degree.
Popular Khet
i
ISSN: 2321
-
0001
6
5
Kumar et al., 2017, Pop. Kheti, 5(4): 63-66

Popular
Article
Amount of Nutrients Fixed by Some Biofertilizers in Various Crops
Microorganisms used as
biofertilizer Nutrient fixed (kg/ha/year) Beneficiary crops
Rhizobium
50 to 300 kg N / ha
Groundnut, Soybean, Redgram, Green-
gram, Black-gram, Lentil, Cowpea,
Bengal-gram and Fodder legumes
Azotobacter
0.026 to 20 kg N / ha
Cotton, Vegetables, Mulberry,
Plantation Crop, Rice, Wheat, Barley,
Ragi, Jowar, Mustard, Safflower, Niger,
Sunflower, Tobacco, Fruit, Spices,
Condiment, Ornamental Flower
Azospirillum
10-20 kg N /ha
Sugarcane, Vegetables, Maize, Pearl
millet, Rice, Wheat, Fodders, Oil seeds,
Fruit and Flower
Blue Green Algae 25 kg N /ha Rice, banana
Azolla 900 kg N /ha Rice
Phosphate solubilizing
bacteria and fungi Solubilize about 50-60% of the
fixed phosphorus in the soil All Crops (non specific)
Constraints in Biofertilizer Technology
Though the biofertilizer technology is a low cost, eco-friendly technology, several constraints limit the
application or implementation of the technology. The constraints may be:
•
Technological constraints like unavailability of good quality carrier material and lack of qualified
technical personnel in production units.
•
Infrastructural constraints like lack of essential equipments, power supply, etc.
•
Financial constraints like non-availability of sufficient funds and problems in getting bank loans.
•
Environmental constraints like seasonal demand for biofertilizers, simultaneous cropping operations and
short span of sowing/planting in a particular locality, etc.
•
Human resources and quality constraints like lack of technically qualified staff in the production units,
lack of suitable training on the production techniques.
•
Unawareness on the benefits of the technology due to problem in adoption of the technology by the
farmers due to different methods of inoculation, no visual difference in the crop growth immediately as
that of inorganic fertilizers.
•
Marketing constraints like non availability of right inoculant at the right place at the right time, lack of
retail outlets or the market network for the producers.
•
The different constraints in one way or the other affect the technique at production, or marketing or
usage.
Conclusion
Biofertilizers being essential components of organic farming play a vital role in maintaining long term soil
fertility and sustainability by fixing atmospheric di-nitrogen, mobilizing fixed macro and micro nutrients
in the soil into forms available to plants. Currently there is a gap of ten million tons of plant nutrients
between removal of crops and supply through chemical fertilizers. In context of both the cost and
environmental impact of chemical fertilizers, excessive reliance on chemical fertilizers is not practicable
in the long run because of the cost, both in domestic resources and foreign exchange involved in setting up
of fertilizer plants and sustaining the production. In this context, biofertilizers would be the viable option
for farmers to increase productivity per unit area.
Popular Khet
i
ISSN: 2321
-
0001
6
6
Kumar et al., 2017, Pop. Kheti, 5(4): 63-66