Archive for December 2016

Natural green

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Title: Weed control and management
Author: Natural green
Rating 5 of 5 Des:

Weed control and management Weed is defined as a plant that is undesirable, unattractive or troublesome especially one t...

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<b><u><span style="font-size: 28.0pt; line-height: 115%;">Weed control and management<o:p></o:p></span></u></b></div>
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<span style="font-size: 14.0pt; line-height: 115%;">               Weed is defined as a plant that
is undesirable, unattractive or troublesome especially one that grows where it
is not wanted and often grows or spreads fast or take the place of desired
plants.<o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">                  The
classification of weeds is important for applying weed management for a
particular group of weed instead of individual weed species. Weeds are
classified according to their life cycle, morphology, structure and form.
According to the life cycle, weeds are classified into three groups. <b>Annua</b>l weed take one year or one season
to complete their life cycle. <b>Biennial</b>
weed take two years or season to complete their life cycle. <b>Perennial</b> weed take more than two years
or several years to complete their life cycle.<o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">                  According
to the habitat weeds are classified into two groups such as terrestrial and
aquatic. According to the morphology, weeds are classified into two groups such
as narrow leaved weeds and broad leaved weeds. Grasses (family Poaceae) and sedge
(family cyperaceae) are the examples for narrow leaved weeds. Grasses have
hollow stem and lignite alternative or opposite leaves with leaf sheath. Sedges
are angular and have solid stem. Broad leaved weeds are dicot plants. The
difference between broad leaved weeds and narrow leaved weed helps to use of
selective control methods without injuring broad lead weeds. <o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">                  Correct
identification, impacts and life cycle of weed are useful to idenify proper
weed management. Several methods are available to control weeds. Preventive
methods are used to stop the spread of weeds. Preventing the introduction of
weeds and spreading is usually easier than controlling them after
establishment. <o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">              Cultural
weed control methods make the crop to be the best completer with the weeds.
Planting the best crop varieties and dense crop populations and applying lime
and fertilizers help to achieve the aim of the cultural weed control. It is
more practicable and efficient method for controlling weeds where other methods
are impossible such as within rows of rice fields. But it is difficult to
distinguish weed seedlings and rice seedlings at early stages so uprooting of
rice seedlings cannot be avoided. It is not practical to apply for large scale
rice fields. <o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">                        Biological
control involves the use of natural enemies to reduce the reproductive
potential of weeds.  They can be weed
feeders like insect feeders or disease cause organisms like fungi, bacteria and
viruses to kill the invasive plants. It is environmentally friendly methods. It
has ability to self-propagative so there is no need of again and again
introducing them for field. Weeds are unable to develop resistance against
biological methods. The damage to the untargeted pant species is minimized due
to its selectivity.  As biological
control agents are also dependent on the environmental conditions, it causes
fluctuations on the weed populations.<o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">                        Chemical
control involves the use of herbicides to kill a particular group of weed. It
is an efficient method for both small scale and large scale. It supports to
kill the deep rooted, vegetative propagative plants. After application, it is
not allowed weed to regenerate for a considerable time period. Unlike other
methods, herbicides are able to reach all places and kill the weeds.  But excess use of herbicides makes the weed to
develop resistance against them. The people who apply the herbicide must have
proper technical knowledge in order to apply the appropriate dose with correct dilution.
 In addition to suppression of growth
weed, it treats to the growth of crop plants as well as animal species. Excess use
of herbicide pollutes the soil, water and the atmosphere.<o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">                        Mechanical
or physical methods destroy or make the environment less favorable for seed germination
and survival.  Mechanical methods are tillage,
uprooting, slashing, moving, ring banking and dark stripping. It requires less
time than the manual control. It is only suitable for small scale weed management.
It cannot be used to control weeds growing much closer to the crop plants.  Improper tillage can damage the crop plants
too. It cannot be used for soil with too dry or too wet conditions. It causes
serve disturbance to the soil which leads to soil erosion. <o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">               Integrated
weed management (IWM) involves employment of different methods of weed
prevention and control. IWM is a combination of physical control, chemical control,
biological control and cultural control method. It reduces the chance to the plants
to adapt to the control techniques. It reduces the weed stock and extent in the
soil. It is the most sustainable method of weed control and management.  But it takes relatively more tim</span><span style="font-size: 16.0pt; line-height: 115%;">e </span><span style="font-size: 14.0pt; line-height: 115%;">for the longer process. <o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">                        Risk
of plant to be invasive is assessed by using a protocol including 32
questions.  At least 28 answers for flora
are essential to evaluate the potential of risk. Each question must be marked
with either yes or no. Using final percentages value for answers with yes, the plant
is placed in one of following categories. <o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">                        >80%-
very high risk<o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">                        60-80%-high
risk<o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">                        40-60%-
moderate risk<o:p></o:p></span></div>
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<span style="font-size: 14.0pt; line-height: 115%;">                        <40%-
low risk<o:p></o:p></span></div>

Weed control and management

Weed control and management Weed is defined as a plant that is undesirable, unattractive or troublesome especially one t...

Seedless non vascular plants (Phylum Pterophyta)

Natural green

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Title: Seedless non vascular plants (Phylum Pterophyta)
Author: Natural green
Rating 5 of 5 Des:

Seedless non vascular plants (Phylum Pterophyta) According to the recent researches, vascular plants a...

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<b><u><span style="font-size: 26.0pt; line-height: 115%;"> Seedless non vascular
plants<o:p></o:p></span></u></b></div>
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<b><span style="font-size: 26.0pt; line-height: 115%;">            </span></b><b><span style="font-size: 22.0pt; line-height: 115%;">(Phylum Pterophyta)<o:p></o:p></span></b></div>
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<span style="font-size: 16.0pt; line-height: 115%;">               According to the recent
researches, vascular plants are evolved from mosses like plants.  They were the first group of plant those had
chance to grown in larger size in the land due to the presence of vascular
system. The vascular system arise from the root system further extends into the
stem and leaves. It facilitates the efficient way of water and nutrients
transport.<o:p></o:p></span></div>
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<span style="font-size: 16.0pt; line-height: 115%;">             The division
Pterophyta can be distinguished from other plant by a vascular system, a
dominant sporophyte and dispersal through spores.  Ferns are also restricted to shady moist
environments. Most are terrestrial. Some float on the aquatic bodies. Some grow
as epiphytes on the tree trunks and rocks in order to get maximum solar energy
for maximum photosynthesis. Most of the ferns are found as herbs and shrubs.
Tree plants are rarely found such <i>Angiospetris</i>.
<o:p></o:p></span></div>
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<span style="font-size: 16.0pt; line-height: 115%;">             The
gametophyte is the short lived one of their life cycles. Their sporophytes and
gametophytes are <b>heteromorphic </b>which
means both of them are differ in morphology. 
Both sporophyte and gametophyte are photosynthetic and can live
independently. <o:p></o:p></span></div>
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<span style="font-size: 16.0pt; line-height: 115%;">             The fern’s
sporophyte is much more complex than that of the mosses. The fern sporophyte
has vascular tissues. It is well differentiated into the stem, roots and
leaves.  The gametophyte is lack of
vascular tissues. <o:p></o:p></span></div>
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<span style="font-size: 16.0pt; line-height: 115%;">             Fern
sporophyte has a horizontal underground stem called rhizome with roots emerging
from their sides. Some have aerial stem. 
The large compound leaves are referred to as fronds. They usually rise
from the tip of the rhizome.  Young
leaves are called as fiddle heads which appear as rolled up coils. The fiddle
heads unroll and develop into the mature leaves.  Most of the ferns fronds are dissected and
feathery<i>. Marselia</i> has fronds which
is four clovers. But they also develop form the piddle heads. <o:p></o:p></span></div>
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<span style="font-size: 16.0pt; line-height: 115%;">                  Some
ferns possess respectively both of photosynthetic vegetative fronds and Non photosynthetic
reproductive fronds that appear in brownish color such as <i>Drymyoglossum</i>. Some have elevated fertile fronds and horizontal
vegetative fronds such as <i>Anemia</i>.
These elevated fronds bear the clusters of sporangia.  Some ferns possess only vegetative fronds but
underside of those vegetative fronds bear clusters of sporangia called as <b>sori</b>. It may or not protected by structure
called indusum. In <i>Marseilie</i>a, the
microsporangia and megasporangia are produced respectively. Those sporangia are
enclosed in special bean shaped structure called as <b>sporacarps</b>. <o:p></o:p></span></div>
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<span style="font-size: 16.0pt; line-height: 115%;">                  Most
Pterophyte are <b>homosporous</b> which
produce spores of one size and they result in producing only one
gametophyte.  Those homosporous ferns
have <b>exosporic</b> <b>development</b> where the gametophyte develops from the outside of the
spore wall.  But a significant number of
ferns are <b>heterosporous</b> which
produce spores of two distinct sizes such tiny microspores and large
megaspores.  The microspores produce the
male gametophyte and megaspores produce female gametophyte.  Those heterosporous are <b>endosporic development</b> where the gametophyte develops inside the
spore wall. <o:p></o:p></span></div>
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<span style="font-size: 16.0pt; line-height: 115%;">                      The
sporangia in the fertile fronds or sorri have thick walled cells on the one
side of the sporangium. It is hygroscopic. The diploid spores mother tissues
undergo meiosis and produce haploid spores. . Under dry conditions, those
hygroscopic cells contract and cause sporangium to release spores. When
favorable conditions receive, spores are germinated and result in producing
haploid gametophyte.  These gametophytes
are heart shaped and in one cell thickness. 
They have rhizoid to anchor themselves to the substrate. <o:p></o:p></span></div>
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<span style="font-size: 16.0pt; line-height: 115%;">                      The
flask shaped archegonia and globular antheridia are produced on either side of
the same or different gametophyte.  The
sperm found in the antheridia have flagella.  When water is present, sperm swim towards the
archegonia through a chemical signal released by the archegonia. After
fertilization, the diploid zygote is produced. The zygote is developed into the
new haploid sporophyte and completes the life cycle. Although ferns also do not
produce seeds, they much advanced form the other seedless vascular plants.  Those vascular plants are considered as <b>polysporangiate</b> which means produce
sporangia more than one. <o:p></o:p></span></div>
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Seedless non vascular plants (Phylum Pterophyta)

Seedless non vascular plants (Phylum Pterophyta) According to the recent researches, vascular plants a...

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Weed control and management

Seedless non vascular plants (Phylum Pterophyta)

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