Special Reports/Organic Farming
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Biofertilisers’ use for raising output
By Khurram
Shahzad & Zeshan
THE rapid growth in population demands increased supply of
food which can be optimised with larger use of inputs such
as fertilisers. The use of nitrogenous, phosphoric and
potassium fertilisers has become indispensable to attain
good crops yield. At the same time, fertiliser prices are
going up day by day due to energy crisis all over the world.
The Haber-Bosch process is generally used for the production
of nitrogenous fertilisers worldwide, which, in addition to
catalyst, requires high temperature up to 800 o F and
pressure above atmospheric one. Therefore, industrial
nitrogen fixation is heavily dependent on energy derived
from fossil fuel which is depleting at a very fast rate and
is getting costlier.
Fixation of molecular nitrogen can also be accomplished by a
group of micro-organisms in soil and root tissues of certain
plants in the presence of an enzyme “nitrogenase” under
normal pressure and temperature that is dependent on energy
from only renewable resources such as products of
photosynthesis and organic materials in soil.
The nitrogenous fertilisers, applied at the recommended
rates for getting higher yields, are also subjected to loss
through various paths to environment and thus resulting in
its pollution. Apart from this, hundreds of kilogrammes of
solid waste are generated daily that can seriously affect
the environment and human health, if not handled properly.
This waste could be converted into useful products such as
compost by providing favourable conditions for indigenous
micro-organisms or by incorporating desired micro-organisms
into it. So the strategy for improving agricultural
production in developing countries should take into account
the in-expensive, environment-friendly, realistic and
programmatic approach.
The term biofertiliser or more approximately microbial
inoculants can be defined as preparation containing live or
latent cells of efficient strains of nitrogen fixing,
phosphate solubilising or cellulytic micro-organisms used
with an objective to increasing the number of these
micro-organisms and accelerating certain microbial process
to augment the extent of the availability of nutrients in
the farms which can be easily assimilated by plants. The
term biofertiliser is used for various types of materials
such as composts, agro-waste, and some liquid cultures of
unidentified miscellaneous microbes.
First of all, Nobbe and Hiltner introduced laboratory grown
cultures of Rhizobia on solid media containing extracts of
leguminous plants, gelatine, sugar, and asparagines in 1895.
In the maiden attempt, 17 different inoculants for important
leguminous crops were produced. The rhizobial inoculants
(also known as legume inoculants) then became industrial
proposition in the United States, Europe, Australia and
India by the beginning of 20th century. In 1920 these got so
popular that in the United States, besides the US Department
of Agriculture and 20 research institutes, 17 commercial
concerns were marketing inoculants. In Russia and Poland,
non-symbiotic bacteria of one genus Azotobacter gained
importance in the early part of 20th century. A product
under the trade name Azotobakterin was prepared for soil and
seed treatments and spectacular benefits were recorded on
the yield of vegetables and cereals.
Following this success of legume inoculants, the
biofertilisers for non legume crops are becoming
increasingly popular in the world in recent years.
Azotobactor inoculants are more common in the world because
these can be applied to non-legume crops and promote seed
germination and initial vigour of pants due to growth
substances produced by the organism. In Pakistan, work on
biofertilisers is being undertaken in different institutions
like the University of Agriculture, Faisalabad, the Ayub
Agricultural Research Institute (AARI) and National
Institute of Biotechnology and Genetic Engineering (NIBGE).
These have lunched their bio-products with different names
like Rice Bioferts, Geraseemi Teeka, Biopower, etc.
Composting is a recycling process in which organic materials
are biologically converted into amorphous and stable humus
like substances under conditions of optimum temperature,
moisture and aeration. It can be understood as a type of
bacteria farming in which favourable environment is created
for micro-organisms to thrive and multiply rapidly,
accelerating the rate of decomposition of organic materials.
It is the controlled decomposition and appropriate
stabilisation of blended organic substrates under aerobic
conditions that allows the development of thermophilic
temperatures as a result of biologically produced heat,
where organic material is decomposed to a level which could
be handled, stored and applied to land without environmental
impacts. So, composting provides a way to manage big volumes
of organic waste in environmentally sound manners.
It has been estimated that about one kilogramme garbage per
person is produced and disposed of daily in our country. In
urban areas, less than 60 per cent waste is collected. No
city in Pakistan has proper waste collection and disposal
system. Bioconversion of that organic waste is one of the
major options, which could be effective for reducing huge
piles of organic wastes and cleans the environment.
Compost is made from mixing together organic waste materials
– such as leaves, farmyard manure, poultry manure, sugarcane
filter cake, weeds and straw – and leaving them to decompose
until a black, crumbly soil is formed. The materials needed
to make it are locally available and accessible. Composting
provides a way not only of reducing the amount of waste that
needs to be disposed of, but also of converting it into a
product that is useful for agriculture, gardening,
landscaping, or house plants. Recycled organic wastes cannot
only act as supplement to chemical fertilisers but may also
improve the physio-chemical properties of soil
Although composting is an old technique, efforts have been
made to improve it with respect to quality of compost and
rate of composting. Heightened environmental awareness has
sparked renewed interest in composting. With the resurgence
of interest in this technology, efforts have been made to
improve it with respect to rate of composting and quality of
the end product. Manipulation of moisture content, pH,
nutrient content ratio and oxygen supply not only increases
composting rate but is also helpful in achieving the product
of desired characteristics. A novel approach could be that
composted material may be converted into value-added product
such as an effective biofertliser by blending plant growth
promoting rhizobacteria (PGPR) which are free living soil
bacteria that can either directly or indirectly facilitate
rooting and growth of plants. Moreover, incorporation of
compost with PGPR could make it a promising biofertilizer.
There are several mechanisms by which the PGPR affects
plants’ growth such as their ability to produce various
compounds (such as phytohormones, organic acids,
siderophores), fix atmospheric nitrogen, solubilise
phosphate and produce antibiotics that suppress deleterious
rhizobacteria, and produce biologically active substances or
plant growth regulators. Production of biologically active
substances or plant growth regulators is one of the major
mechanisms through which PGPR influences the plant growth
and development.
Plant growth regulators are the organic compounds which even
at low concentration have shown far-reaching effects on
growth and development of plants. Therefore, direct use of
micro-organisms to promote plant growth continues to be an
area of rapidly expanding research and is currently
attracting considerable attention of the microbiologists to
increase growth and yield of crop plants. The use of PGPR to
enhance plant growth and crop yield is predicted to become
an emerging trend in contemporary agriculture in the near
future.
Several researchers of the world have reported the effect of
biofertilisers or compost for improving growth and yield of
various crops which are being highlighted here. Some
Pakistani scientists in 1996 conducted a field experiment to
study the effect of azotobacter inoculation on growth and
yield of wheat (cv. Inqab) in the presence of NPK
(150-25-50). The data revealed that seed inoculated with
various azotobacter cultures significantly increased grain
yield (38.5 per cent), straw yield (15.3 per cent), number
of tillers (12.5 per cent), spikelets (10.7 per cent) and
1000-grain weight (7.3 per cent) compared with un-inoculated
control.
Some scientists compared the effect of traditional
commercial fertiliser, compost and barnyard manure.
According to their results of a two-year field experiment of
wheat, compared to the control, the increases of the grain
yield by the application of commercial fertiliser, different
doses of compost and barnyard manure were observed as 21 per
cent, 18-29 per cent and 32 per cent, respectively.
The biofertiliser or compost enriched with nutrients, plant
growth regulators or PGPR can be used to increase per unit
yield of crops on sustainable basis. This approach can help
us to obtain high yield potential on one hand and reduce
dependence on chemical fertilisers on the other hand without
compromising per unit yield. This environment- friendly
strategy can also help in tackling the pollution problem
created due to the piling up of huge volumes of poisonous
organic wastes.
The following considerations can be helpful in future for
development of biofertlisers: Finding out keys to
specificity of nitrogen fixing organism to selected plants;
acquiring the property of nitrogen fixation by other
non-nitrogen fixing micro-organism; evolving nitrogen-fixing
plants; exploiting other plant-micro-organism associations;
efficiently exploiting the non-biological systems of
nitrogen fixation, and recycling of wastes for utilising
nutrients.
Courtesy: The DAWN |
Pakissan.com;
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