Soil profile
A soil profile is a cross section through the soil which reveals its horizons (layers). Soil generally consists of visually and texturally distinct layers, which can be summarised as follows, from top to bottom:
- A)
Humus:
organic
matter
in
relatively
undecomposed
form.
This
layer
tends
to
be
dark
and
rich
in
smell
and
texture.
Raw,
semi-decomposed
organic
matter
may
be
recognisable
amongst
its
components,
e.g.,
leaf
mold,
twiggy
material,
etc.
- B)
Topsoil:
well
decomposed
organic
matter,
mixed
with
a
smaller
amount
of
minerals.
- C)
Layer
of
mixed
decomposed
organic
matter
and
mineral
content.
- D)
Subsoil
or
mineral
layers,
the
content
of
which
varys
according
to
the
nature
of
the
soil
and
its
parent
material.
- E)
Bedrock
or
parent
material,
which
breaks
down
at
the
upper
surface
due
to
the
effects
of
weathering
and
decay.
The
nature
of
the
original
parent
material
determines
the
soil's
composition
and
is
itself
the
result
of
geological
processes
(e.g.,
glaciation,
volcanic
activity,
etc.,
that
have
dominated
in
the
region).
Although soil is divided into visually discrete horizons, constant movement occurs between them due to weathering, water movement, and the actions of soil life such as worms and bacteria, causing organic matter to move downward and mineral matter to travel upward. A soil profile can also reveal other valuable information, including evidence of compaction, water logging, root penetration, and so on.