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Archives (2003)
Bacteria in weed
as biofertilizer for cotton
by
Likha Cuevas |
April-June
2003
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A team of scientists has discovered a species
of bacteria found in the roots of Cenchrus echinatus L., (from
the family of grasses) that can help in fixing nitrogen in
the soil.
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| Bacillus cereus |
We always thought that grasses are just pesky
plants that keep on sprouting and competing with cultivated
crops. But unknown to most of us, at the roots of some grasses
beneath the soil there live some of the most beneficial microorganisms
that can help farmers in their crops.
The team of Dr. Victoria B. Cosico, Magdalena
C. Damo, and Victoria Puyot of the Cotton Development Administration
(CODA) in Batac, Ilocos Norte has discovered a species of
bacteria found in the roots of Cenchrus echinatus L., (from
the family of grasses) that can help in fixing nitrogen in
the soil. This bacterium is Bacillus cereus, a non-symbiotic
biological nitrogen fixer that may provide crops like cotton
the nitrogen requirements they need.
Role of nitrogen
Why do crops need nitrogen (N)? This element is an essential
nutrient for life because it is an important component of
proteins, nucleic acids, and other cellular constituents of
living and some non-living (viruses, prions, etc.) organisms
on earth. Although 78% of the atmosphere is composed of nitrogen
(N2), organisms cannot use this in its gaseous form. Plants
can only use nitrogen in the form of nitrate or ammonium ions
and animals can only use it in organic forms, which they get
by consuming plants or other animals. One way of converting
nitrogen into usable forms is by the use of a microbial process
called 'nitrogen fixation'.
According to Cosico, Damo, and Puyot, the discovery
of symbiotic and non symbiotic biological nitrogen fixers
(BNF) associated with some weed species led to the microbial
formulations now commercialized for some crops. The research
team also said that symbiotic (the intimate living together
of two dissimilar organisms in a mutually beneficial relationship)
BNF are commonly crop generic-specific while free-living BNF
usually are within the rhizosphere (root zone) such that the
biologically fixed N would be just close to the root system
ready for use.
B. cereus as
nitrogen fixer for cotton
Generally, it was observed that agronomic and yield response
of cotton to the application of organic fertilizers alone
is inferior compared to that of the recommended inorganic
fertilizer rate. However, the results of the combination of
organic and inorganic fertilizer were comparable with the
results of the inorganic fertilizer application, the researchers
said.
Many weed species in cotton production sites
are associated with the crop during growing season and the
possible existence of BNF associated with the weeds can indirectly
benefit cotton plants. The team studied this possibility so
that this BNF can be used to enrich organic fertilizers with
nitrogen to enhance crop performance. They were able to screen
and identify the nitrogen-fixing bacteria associated with
cotton weeds, which is B. cereus. They also enhanced the value
of these bacteria as cottonseed microbial inoculants for early
seedling establishment. The effects of the nitrogen-enriched
organic fertilizer was determined by the isolate (B. cereus)
on the agronomic and seed cotton yield performance.
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| Cenchrus echinatus |
The results of this study showed that B. cereus
isolated from the roots of the grass Cenchrus echinatus L.
can be used as a microbial seed inoculant (the introduction
of the bacteria in seeds) to improve seedling vigor. In an
experiment conducted involving bio-organic fertilizer or BOF
(prepared compost material biologically enhanced with a type
of fungi, Trichoderma sp.), BOF with B. cereus, chicken manure,
and BOF with B. cereus had germinated more seeds than other
treatments in the sand boxes. As for the seedling vigor index
(SVI), the BOF as carrier of the B. cereus showed the highest
effect on the SVI. The bacteria also significantly affected
fresh seedling weights of the cotton variety UPLC-2.
"If B. cereus is used to bio-enrich the
organic fertilizer with nitrogen and combined with half of
the recommended nitrogen fertilizer rate in cotton production,
the quantity of substituted nitrogen is within the range of
37.5-65 kg/ha," the researchers concluded. In the screen
house and field conditions, the bacteria combined with bio-organic
fertilizer gave comparable agronomic performance and seed
cotton yield. The cotton plants with this nitrogen enhanced
BOF grew luxuriantly and developed minor fruit-bearing branches.
How could these bacteria help farmers? "In
so far as our results are concerned, it would lessen the use
of inorganic fertilizers, particularly nitrogen." Cosico
said. According to the researchers, most formulations of BNFs
can substitute 1/2 of the recommended amount of N of a crop
since the N-fixing organisms provide the other requirements
of the crop, like cotton. The bacteria with organic fertilizer,
applied with half of the recommended inorganic fertilizer
rate, would supplement the requirement of N for plant use,
given the proper soil environment, which is moist soil. Farmers
would be able to save because they will apply less commercial
inorganic fertilizers.
Future studies
To make the B. cereus formulation easier to apply for farmers'
use, the work on this study should be continued. However,
due to budgetary constraints, the project has been stalled
for a while. A study is needed to make a better microbial
formulation and that will make B. cereus easier to store and
handle. The researchers suggested that B. cereus can be lyophilized
(or freeze-dried) and formulated as powder or as a liquid
concentrate since the bacteria can develop spores. "It
can be applied through soil injections close to the root system
for more effective use of the nitrogen fixed by the organism,"
the team said. This can be possible if the bacteria are prepared
as liquid formulation.
The researchers hope that, "there will
be lesser use of expensive imported inorganic N fertilizer
and B. cereus will also enrich the soil." In the future,
this bacteria discovered from weeds could also be applied
to other crops.
Not bad, coming from weeds.
References: Cosico, V.B., Damo, M.C., and
Puyot, V. Bacillus cereus: A New Biological N2-Fixing Organism
From the Rhizosphere of Cenchrus echinatus L. and its Utility
as Biofertilizer in Cotton Production.
Deacon, J. The Microbial World: The nitrogen cycle and nitrogen
fixation. University of Edinburgh. http://helios.bto.ed.ac.uk/bto/microbes/nitrogen.htm
The future of symbiotic nitrogen fixers in agriculture. http://tornado.breward.edu/kroizsr/
ecol350paper.html 
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