APPLICATION OF ALLELOPATHY IN AGRICULTURE
Allelopathy is derived from two Allelon means to each other and Pathos means to
suffer. Allelopathy refers to the detrimental effects of higher plants of one
species (the donor) on the germination, growth of the development of the plants
of another species (the recipient).
Brief History Of Allelopathy
Theophrastus and Democritus in the 5th and 3rd
century B.C. was recognized the impact of Allelopathy on Agriculture. In 1832
Decandolle worked on the Allelopathy field. The
word of Allelopathy was first time introduced in 1937 by Molisch .
Allelochemicals:
The secondary metabolites produced by the plants, have the Allelopathy
effect on the growth and development of another plants.
Occurrence of the allele-chemical:
Roots and Rhizomes of the plants contain low amount of
allelochemical.
In the stems of the plants.
High amount of allelochemical are found in the leaves.
Flowers and pollens also have.
Allelochemical are also present in the seeds and fruits of the
plants.
Mode Of Allelochamical Release
Volatilization:
Allelo-chemicals may
volatilize and be absorbed directly by the plants through atmosphere or may be
taken up through the soil solution when these chemicals are gone into the soil
through the dew.
Leaching:
Leaching is the removal of the water soluble substances from the
plant body through the rain, dew, mist and fog.
Root exudates:
Root exudates are those substances which are released through the
roots of the plant into the surrounding medium. A variety of the allelopathic
chemicals are released through roots of the plants which effect the growth of
the microorganisms and higher plants.
Decomposition of the crop residues:
Large amount of the allelochemicals are released through the
decomposition of the crop residues into the soil and also into the atmosphere.
Factors Effecting Of Production Of Allelo Chemicals
Radiation
Mineral deficiency
Water stress
Temperature
Allelopathic agents
Age of the plant
Genetics
Mode Of Action Of Alleo-Chemicals
Cell division
Cell elongation
Phytochrome induced growth
Permeability of cell membrane
Availability of P & K
Mineral uptake
Stomatal opening and photosynthesis
Respiration
Protein synthesis
Clogging and corking of xylem
Crop- Crop Intrection
The field crops gradually add the phytotoxins to the soils mainly
through the crop residues and root exudates.Factors affecting the production of
phytotoxins:
Type of the crop
Age of the plant
Microorganisms
Soil aeration
Tillage practices
Effect Of The Pytotoxins On The Crop Plants
1.
Inhibition
of nitrification and biological nitrogen fixation
2.
Predisposing
the plants to diseases
3.
Inhibition
or simulation of germination growth and yield
4.
Plants
produced the chemicals which may be harmful for it or for the other plants
through
5.
Delayed
or complete inhabitation of germination
6.
Reduced
the plant population
7.
Stunted
growth and deformed the roots and shoots
8.
Deranged
the nutrients absorption
9.
Lack
of seedling vigour
10.
Reduced
tillering
11.
Chlorosis
12.
Wilting
13.
Predisposition
to root rot and seedling death
Some Crops Who Has The Allelopathic Effect On Other Crops
Wheat
The decomposing wheat residues contain primary organic acids such
as phenolic acid. Wheat residues added 1.5 tonnes phenolic acid per acre under
no tillage condition. Wheat straw inhibited seed germination, decreased root
and shoot growth, shortened internodes and reduced the grain yield of wheat. Decomposing
of wheat straw may inhibit the root growth of barley.
Corn
Decomposing of corn residues decreased the respiration of tobacco
seedlings and causes chlorsis and stunted growth of maize and inhibited the
nitrification process in the soils.
Rice
The allelochemicals released by the decomposition of the rice residues
cause the effect on the growth of rice seedling and decreased the yield of
rice. Nodulation process, biological nitrogen fixation and grain yield also
reduced in soybean by rice stubbles.
Rye
Decomposition of rye residues inhibits seed germination, seedling
emergence and radical elongation of the rye seedling.
Oat
Oat straw was more toxic at
the maturity and its toxicity remains up to 8 weeks after decomposition. Aqueous
extract of decomposing oat residues were inhibitorier to seedling growth of the
test species.
Sorghum
It proves harmful for the maize, oat and wheat growth. It proved
inhibitorier to small seeded, broad leaf species. The aqueous extract of
sorghum stubble inhibited the seed germination and root growth.
Barley
Decomposing barely residues became phytotoxic 7-10 days after
incorporating in the soils toxicity reached peak at 20 days and declined after
45 days.
Clover
Aqueous extract of clovers caused poor and abnormal seed
germination and depressed seedling growth.
Soybean
Soil microorganisms form the
inhibitory substances from the decomposing of the soybean residues. An aqueous extract inhibit the seed
germination soybean, alfalfa and many other.
Sunflower
·
Reduced
the growth of sorghum seedling
·
Inhibit
the seed germination
·
Brassica
oilseed crop
·
Stunted
the plant and reduced the dry weight
·
Inhibition
of germination
·
Sugarcane
·
Inhibit
the growth of young sugarcane plant
·
Decrease
the stem and leaf growth
Tobacco
Effect on germination, root and shoot length and seedling vigour of
rice
Increased the height, specific leaf weight and chlorophyll content
in maize
Root Exudates
They effects plants Germination, growth and yield of different
crops. Sorghum and maize root exudates inhibited the growth of sesame plants. Root
exudates of white clover and soybean decreased the dry weight of radish. Tomato
root exudates decrease the seedling growth of lettuce. Root exudates of jute
stimulated the root and shoot growth of wheat.
Croping Systems
There are three type of cropping systems
Monoculture
Crop rotation
Crop mixture
Monoculture
Monoculture is the growing of the same crop on the same land. In
the monoculture the inhibitory effect of allelochemical is more due to
accumulation of the phytotoxin over the period of time and rises the problem of
i.
Auto
toxicity and soil sickness
ii.
Auto
toxicity
iii.
Auto
toxicity is the accumulation of phytotoxins from decomposing plant residues,
root exudates and from the multiplication of the harmful pathogen in the soil.
iv.
Soil
sickness
v.
Phytotoxic
material released from plants or plant residues may be accumulated in the soils
through the physical absorption.
vi.
Continues
cropping of oat, wheat and barley caused the problem of soil sickness
vii.
Soil
sickness occurring due to
viii.
Unbalanced
use of the nutrients
ix.
Destruction
of the soil structure and physical properties of the soil
x.
Evolution
of the phyto-pathogenic micro-flora
xi.
Increased
the production of weeds and pest
xii.
Change
in the soil ph
xiii.
Accumulation
of phytotoxin in the soil
Crop Weed Interaction
Crop exert allelopathic effects on the other crops and also on the
weeds. They inhibit or stimulate the germination and growth of the weeds through
Seed leachates
The seed leachates of the some crop particularly during the
germination, liberate inhibitors. This may decrease or increase the seed
germination and growth of certain weeds species. The seed leachates of barley,
sorghum, cucumber, sugar beet and maize pollens inhibited the seed germination
and seedling growth of weeds
Root exudates
The root exudates play a significant role in living plant and may
inhibit or stimulate the seed germination or seedling growth of associated
weeds. The root exudates of the rye, corn, wheat, oat, rice, sorghum and
sunflower inhibited the seed germination and seedling growth of weeds. On the
other hand root exudates of the sorghum stimulate the seed germination of red
sorrel.
Crop residues /growth
The growing crops suppress the growth of certain weeds species,
while the residues of some crops also inhibited the seed germination and
seedling growth of weeds through the released of phyto toxins. Crop residues
left on the surface of the soil suppress the germination and growth of the
weeds through the leaching of chemicals.
CROP ALLELOPATHY FOR THE WEED CONTROL
1.
The
potential of the allelopathy of the crops should be used for the management of
the weeds through
2.
Development
of the cultivars that would release the allelochemicals as natural herbicide
provide a satisfactory weed control
3.
Utilization
of the allele-plants which does not interfere the crop growth
4.
Ploughed
under to control the weeds through root exudates or decomposing the crop
residues
5.
Research
on the weed control has amid to
6.
Identify
the cultivar and accessions with the high allelopathic potential
7.
Isolate
allele-chemicals
8.
Develop
field techniques for the use of crop to control the weeds
Weed-Crop Interaction
1.
Under
the field condition weeds infestation is one of the major cause of the yield
reduction in crops
2.
The
loss in the yield is due to
3.
Weeds
released the allele-chemicals
4.
Competition
5.
Acting
as an alternative host of diseases and insects
6.
The
residues of the weed may exert the alleloptathic effect on the crop plants
similar to the crops through
7.
Inhibition
of the biological nitrogen fixation by the certain weeds
8.
Nutrients
uptake by the weeds
9.
Inhibitory
effect on the seed germination, growth and yield
10.
Weeds
effects on the crop through
11.
Residues
of the weed plant
12.
Root
exudates
13.
Leaf
secretions
14.
Volatilization
Exploitation Of Allelopathy For Crop Productopn
·
Phytotoxic
mulches and cover crops are used to inhabitation of the germination and growth
of weeds in the field
·
Crop
rotations, crop mixtures and intercropping are used for controlling the weeds
through allele-chemicals released by the different crop plants
·
Living
crop interference
·
Use
of the trap crops to control the parasitic weeds
·
Through
the breeding of weed suppressing crop varieties
·
Use
of the tree litter for the control of weed
·
Use
of the herbicide which arises from the natural products to overcome the problem
of weed infestation
