Biofertilizers are the
most advanced biotechnology necessary to support developing organic
Agriculture, sustainable agriculture, green agriculture and non-pollution
agriculture. Bio Fertilizer are natural and organic fertilizer that helps to
keep in the soil with all the nutrients and live microorganisms required for
the benefits of the plants. Today product like biofertilizers using the
biotechnology techniques have proved that biological control is widely regarded
as a desirable technique for controlling insects and pests, due to its minimal
environmental impact and its avoidance of problems of resistance in the vectors
and agricultural pests.
Increasing use of
chemical fertilizers in agriculture make country self dependent in food
production but it deteriorate environment and cause harmful impacts on living
beings. Due to insufficient uptake of these fertilizers by plants results,
fertilizers reaches into water bodies through rain water, causes eutrophication
in water bodies and affect living beings including growth inhabiting micro
organism. The excess uses of chemical fertilizers in agriculture are costly and
also have various adverse effects on soils i.e. depletes water holding
capacity, soil fertility and disparity in soil nutrients. It was felt from a
long time to develop some low cost effective and eco-friendly fertilizers which
work without disturbing nature. Now, certain species of micro-organism are
widely used which have unique properties to provide natural products, and serve
as a good substitute of chemical fertilizers.
At this critical juncture,
biofertilizers are useful supplement to chemical fertilizers. Organic farming
has emerged as the only answer to bring sustainability to agriculture and
environment. Biofertilizers is also an ideal for practicing organic farming.
What is biofertilizer?
A number of
micro-organisms (bacteria fungi and algae) are considered as beneficial for
agriculture and used as biofertilizers.
Why biofertilizers?
Biofertilizers are
supposed to be a safe alternative to chemical fertilizers to minimize the
ecological disturbance. Biofertilizers are cost effective, eco-friendly and
when they are required in bulk can be generated at the farm itself. They
increase crop yield upto 10-40% and fix nitrogen upto 40-50 Kg. The other plus
point is that after using 3-4 years continuously there is no need of
application of biofertilizers because parental inoculums are sufficient for
growth and multiplication. They improve soil texture, pH, and other properties
of soil. They produces plant growth promoting substances IAA amino acids,
vitamins etc. They have 75% moisture and it could be applied to the field
directly. Biofertilizers contained 3.5% - 4% nitrogen, 2% - 2.5% phosphorus and
1.5% potassium. In terms of N: P: K, it was found to be superior to farmyard
manure and other type of manure (Mukhopadhyay, 2006).
Microbes used as
Biofertilizer
Microbes are effective
in inducing plant growth as they secrets plant growth promoters (auxins,
abscisic acid, gibberellic acid, cytokinis, ethylene) and enhance seed
germination and root growth. They also play a considerable role in
decomposition of organic materials and enrichment of compost.
Nitrogen fixing
Bacteria
1. Rhizobia: - Legumes
plants have root nodules, where atmospheric nitrogen fixation is done by
bacteria belonging to genera, Rhizobium, Bradyshzodium, Sinorhizobium,
Azorhizobium and Mesorhizobium collectively called as rhizobia. When rhizobial
culture is inoculated in field, pulse crops yield can be increased due to
rhizobial symbiosis (Dubey, 2001). Rhizobium can fix 15-20 N/ha and increase
crop yield upto 20%.
2. Azorhizobium: It is
a stem nodule forming bacteria and fixes nitrogen symbionts of the stem nodule
also produce large amount of IAA that promotes plant growth.
3. Bradyrhizobium:
Bradyrhizobium is reported a good nitrogen fixer. Bradyrhizobium strain
inoculation with Mucuna seeds enhances total organic carbon, N2, phosphorus and
potassium in the soil, increases plant growth and consequently plant biomass,
reduction in the weed population and increased soil microbial population..
Diazotrophs
These are aerobic
chemolithotrophs and anaerobic photoautotrophs. These are non nodule forming
bacteria. They include numbers of the families:-
1) Azotobacteracae:
e.g. Azotobacter:
They are the free
living aerobic, photoautotrophic, non-symbiotic bacteria. They secretes
vitamin-B complex, gibberellins, napthalene, acetic acid and other substances
that inhibit certain root pathogens and improves root growth and uptake of
plant nutrients. It occurs in the roots of Paspalum notatum (tropical grasses)
and other spp. and adds 15-93 Kg N/ha/annum on P. notatum roots (Dobereiner et
al., 1973). Azotobacter indicum occurs in acidic soil in sugarcane plant roots.
It can apply in cereals, millets, vegetables and flowers through seed,
seedlings soil treatment.
2) Spirillaceae: e.g.
Azospirillum and Herbaspirillum:
These are gram
negative, free living, associative symbiotic and non-nodule forming, aerobic
bacteria, occurs in the roots of dicots and monocot plants i.e. corn, sorghum,
wheat etc. It is easy to culture and identify. Azospirillum is found to be very
effective in increasing 10-15% yield of cereal crops and fixes N2 upto 20-40%
Kg/ha. Different A. brasiliense strains inoculation in the wheat seed causes
increase in seed germination, plant growth, plumule and radicle length.
Herbaspirillum species occurs in roots, stems and leaves of sugarcane and rice.
They produce growth promoters (IAA, Gibberillins, Cytokinins) and enhance root
development and uptake of plant nutrients (N, P & K).
3) Acetobacter
diazotrophicus:
Another diazotroph is
Acetobacter diazotrophicus occurs in roots, stem and leaves of sugarcane and
sugar beat crops as nitrogen fixer and applied through soil treatment. It also
produces growth promoters e.g. IAA and helps in nutrients uptake, seed
germination, and root growth. This bacterium fixes nitrogen upto 15kg /ha/year
and enhance upto 0.5 – 1% crop yield (Gahukar – 2005-06).
Cyanobacteria (Blue
green algae):
Nostoc, Anabaena,
Oscillatoria, Aulosira, Lyngbya etc. are the prokaryotic organisms and
phototropic in nature. They play an important role in enriching paddy field
soil by fixing atmospheric nitrogen and supply vitamin B complex and growth
promoting substance which makes the plant grow vigorously. Cyanobacteria fixes
20-30 Kg/N/ha and increase10-15% crop yield when applied at 10 Kg/ha.
Azolla – Anabaena
symbiosis
It is a free floating,
aquatic fern found on water surface having a cyanobacterial symbiont Anabaena
azollae in their leaves. It fixes atmospheric nitrogen in paddy field and
excrete organic nitrogen in water during its growth and also immediately upon
trampling. Azolla contributes nitrogen, phosphorus (15-20 Kg/ha/month),
potassium (20-25 kg/ha/month) and organic carbon etc. and increases 10-20%
yield of paddy crops and also suppresses weed growth. Azolla also absorbs
traces of potassium from irrigation water and can be used as green manure
before rice planting. Azolla spp. are metal tolerant hence, can be applied near
heavy metal polluted areas.
Phosphate Solubilising
Bacteria
Pseudomonas
fluorescens, Bacillus megatherium var. phosphaticum, Acrobacter acrogens,
nitrobacter spp., Escherichia freundii, Serratia spp., Pseudomonas striata, Bacillus
polymyxa are the bacteria have phosphate solubilising ability.
‘Phosphobacterin’ are the bacterial fertilizers containing cells of Bacillus
megatherium var. phosphaticum, prepared firstly by USSR scientists. They
increased about 10 to 20 % crop yield (Cooper, 1959) and also produces plant
growth promoting hormones which helps in phosphate solubilising activity of
soil.
Phosphate solubilizing
fungi
Some fungi also have
phosphate dissolving ability e.g. Aspergillus niger, Aspergillus awamori,
Penicillium digitatum etc.
Plant Growth Promoting
Rhizobacteria (PGPR)
They are also called as
microbial pesticides e.g. Bacillus spp. and Pseudomonas fluorescence. Serratia
spp. and Ochrobactrum spp. are able to promote growth of plants. Pseudomonas
fluorescence application to the Black pepper enhanced uptake of nutrients which
increased plant biomass. Fluorescent rhizobacteria improve the growth of H.
brasiliensis.
Mycorrhiza
Mycorrhizas are
developed due to the symbiosis between some specific root inhabiting fungi and
plant roots and used as biofertilizers. They absorb nutrients such as
manganese, phosphorus, iron, sulphur, zinc etc. from the soil and pass it to
the plant. Mycorrhizal fungus increases the yield of crops by 30-40% and also
produces plant growth promoting substances.
VAM fungi or
Endomycorrhiza
They occur commonly in
the roots of crop plants. VAM fungal hyphae enhance the uptake of phosphorus
and other nutrients that are responsible for plant growth stimulation including
roots and shoot length. VAM also enhances the growth of black pepper and
protects from Phytophthora capsici, Radopholus similis and Melvidogyne
incognita (Anandraj et al., 2001). VAM fungi enhance water uptake in plants and
also provide heavy metals tolerance to plants.