L4 : O; A Horizon - Soil, Science, Class 7 Video Lecture

hello friends this video on soil pad for
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learn about each of the soil horizons in
more detail so we will start with the
topmost layer that is over ensign so
this is also called as the self phase
horizon so that is the layer which we
see from above the topmost layer that is
the horizon an OTT of organic content
now see it is like obvious that it will
have organic content because it is the
topmost layer so many were their leaves
fall off the trees so wherever there is
anything which is an insect died and it
fall fell off on the ground so it is all
in contact with the topmost layer and
all these things all living organisms
are organic matter they are all carbon
containing compounds so this arisin has
at least a minimum of 20% organic matter
by mask so this is the minimum amount of
organic matter that must be present in
this layer so 20% of organic content is
at least present here so this layer
again it is not necessary that
everywhere the soil horizon will be
better for these specific layers only
now in some places over eyes and might
be present in some other places it might
not be present because this layer is
mostly seen in areas where there is high
production of leaf litter when I say
that I mean whether you think that there
will be more leaf litter whether you
have more trees so mostly the forest
areas so in the forest areas the soil
has this over eysan now there is if you
look at areas where there are no trees
no plants or the chances of leaves
falling off on this topmost layer is
also very less so in those regions this
o horizon might not be present at all so
this over isin actually contains organic
matter which are active
current stages of decomposition because
this organic matter let us consider this
leaf which fell on the ground
so this leaf now it has dried it is
dying so over a period of time it will
start to decompose now as time passes by
it eats to going deep inside the soil
now as long as it remains on the topmost
layer the surface layer it is may be in
the stage of decomposition it is may be
at a particular stage of decomposition
so that is why it is said that oh
horizon is present only in areas where
there is too much production of leaves
that is dead leaves and in this layer
the organic matter is seen to be at
different stages of the composition that
is it has not be composed completely now
due to the presence of organic content
it is generally black or dark brown in
color so here you can see this is the
over ensign so now this topmost layer
might not be present in a lot of areas
so the next layer is a horizon that is
just below the horizon so this is also
quite the mineral horizon because this
is the most important horizon where a
lot of minerals are present at these
minerals are needed by the clams for
their growth so when you compare it with
the underlying horizon that is the
horizons which are present even below a
horizon like B or C horizon so the
texture of a horizon is like more coarse
so when you compare it with underlying
horizons it is also known as the topsoil
why is that for topsoil you might ask
this because it is not the topmost layer
in over eysan is above a horizon that's
because o arisin might be present
somewhere
we present somewhere else but a horizon
is present everywhere so in certain
areas a horizon might not be the topmost
layer but in a lot of areas it could be
the topmost here so that is why it is
termed as the topsoil
it contains minerals and it also
contains minerals like sand clay silt so
all these things are present in this a
horizon now you might ask what is silt
so we are going to discuss about that
when we learn about types of soil this
is also rich in organic content so here
also you find a lot of organic content
because as I said the upper layers will
be rich in organic content because the
dead plants and animal remains they come
in contact with the upper surface and
then this time decomposition so the over
aizen level they are just be composing
that's why they are at different stages
of decomposition by the time they reach
a horizon they are maybe they have
decomposed or they're yet still
decomposing so there also you have lot
of organic content and since organic
content is present therefore the adds to
the fertility of the soil so that's like
the minerals nutrients everything which
a plant needs that is provided by the
topsoil if you look at its color it is
again black or dark brown in color
because organic content they are
generally a dark in color this layer is
predominantly the surface near of many
soils especially in the agricultural
land so then we consider land with all
where you do not have lot of leaf litter
so there the a horizon is like the
topmost layer or the surface layer
looking at its properties it is soft and
porous so you if you actually feel the
texture of the soil of this a horizon
you see that they are soft and they are
also porous now what is the meaning of
porous that means they have lot of pores
in them so when you have lot of pores it
actually allows
water to pass through it so when you
water the plants you actually put water
on the soil so the soil can easily pass
through the a horizon and it can reach
the B horizon now this a Verizon is
extremely important do you know why
because it is home for many organisms
down at the beginning of the nest and I
told you that soil acts as a home where
any organisms like earth wall so these
organisms they live in this snare of
soil so they do not live very deep
inside the soil so they live somewhere
somewhat towards the upper layer of the
soil and a horizon is their home it is
also responsible for soil fertility why
how does it provide fertility to the
soil because a horizon contain Juma's
and what is humours yuma's is obtained
from natural deaky of plants or animals
so this is dark brown or in fact it is
black late weather most of the cases so
due to this press due to the presence of
the Zoomers the organic content of the
soil increases and the fertility of the
soil also inclusions provide support to
plant roots because the roots of the
plants they actually bind or they
actually formally get stuck to the soil
at this layer so that means it means
also providing structural support to the
plants to retain more water as I
mentioned that this layer is soft that
porous now it has pores so these pores
are used to store water and that's how
it holds more water and what is the
benefit of holding water this water can
be utilized by the plants and how do
plants utilize these water through their
root hairs through their root hairs they
will absorb water which is stored in the
pores of the soil and that sour plants
can grow and develop so basically a
horizon plays a very important role as
far as growth of plant is considered
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