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1. Soil Horizon - A layer of soil,
approximately parallel to the surface,
having distinct characteristics produced
by soil forming processes.
Soil Profile - A vertical section of the soil
extending through all its horizons and
into the parent material.
Soil Profile Descriptions

2. Soil Profile - A vertical section of the soil
extending through all its horizons and into the
parent material.
Soil Horizon - A layer of soil, approximately
parallel to the surface, having distinct
characteristics produced by soil forming
processes.
Soil Layer - A layer in the soil deposited by a
geologic force (wind, water, glaciers, oceans,
etc.) and not relating to soil forming process.
Definitions

3. Eluviation occurs in the E Horizon. The E Horizon is also known as
the Zone of Leeching. By definition, eluviation is the process of
removal of materials from geological or soil horizons. Essentially, this
is where most of the weathering occurs in the soil.
Illuviation occurs in the B Horizon. The B Horizon is also known as
the Zone of Accumulation. By definition, illuviation is the deposition
in an underlying soil layer of colloids, soluble salts, and mineral
particles leached out of an overlaying soil layer. In layman's terms, this
is where the particles end up in the B Horizon after they are weathered
from the A Horizon.
Eluviation and Illuviation

4. A: An A horizon is a mineral horizon. This horizon
always forms at the surface and is what many people
refer to as topsoil. Natural events, such as flooding,
volcanic eruptions, landslides, and dust deposition can
bury an A horizon so that it is no longer found at the
surface. A buried A horizon is a clear indication that
soil and landscape processes have changed some
time in the past. Compared to other mineral horizons
(E, B, or C) in the soil profile, they are rich in organic
matter, giving them a darker color. The A horizon,
over time, is also a zone of loss – clays and easily
dissolved compounds being leached out – and A
horizons are typically more coarse (less clay)
compared to underlying horizons (with the exception of
an E horizon). Additions and losses are the
dominant processes of A horizons.
A horizon

5. B: A B horizon is typically a mineral
subsurface horizon and is a zone of
accumulation, called illuviation. Materials
that commonly accumulate are clay, soluble
salts, and/or iron. Minerals in the B horizon
may be undergoing transformations such as
chemical alteration of clay structure. In
human modified landscapes, processes
such as erosion can sometimes strip away
overlying horizons and leave a B horizon at
the surface. Such erosion is common in
sloping, agricultural landscapes. A bulldozer
preparing land for a new subdivision can
also leave a B horizon at the surface. The
dominant processes in a B horizon
are transformations and additions
B horizon

6. C: A C horizon consists of parent
material, such as glacial till or lake
sediments that have little to no
alteration due to the soil forming
processes. Low intensity processes,
such as movement of soluble salts or
oxidazation and reduction of iron
may occur. There are no dominant
processes in the C horizon; minimal
additions and losses of highly
soluble material (e.g., salts) may
occur.
C horizon

7. O: An O horizon has at least 20% organic matter by mass.
Two main scenarios result in the formation of an O horizon:
saturated, anaerobic conditions (wetlands) or high production
of leaf litter in forested areas. Anaerobic conditions slow the
decomposition process and allow organic material to
accumulate. An O horizon can have various stages of
decomposed organic matter: highly decomposed, sapric;
moderately decomposed, hemic; and minimally decomposed,
fibric. In a fibric O layer, plant matter is recognizable (e.g., it
is possible to identify a leaf). Sapric material is broken down
into much finer matter and is unrecognizable as a plant part.
Hemic is in between sapric and fibric, with some barely
recognizable plant material present. It is possible to have
multiple O horizons stacked upon one another exhibiting
different decomposition stages. Because of their organic
content, these horizons are typically black or dark brown in
color. The dominant processes of the O horizon are additions
of organic matter.
O horizon

8. E: The E horizon appears lighter in color than
an associated A horizon (above) or B horizon
(below). An E horizon has a lower clay content
than an underlying B horizon, and often has a
lower clay content than an overlying A
horizon, if an A is present. E horizons are
more common in forested areas because forests
are in regions with higher precipitation and
forest litter is acidic. However, landscape
hydrology, such as perched water tables, can
result in the formation of an E horizon in the
lower precipitation grasslands, as seen in the
profile below. The dominant processes of an
E horizon are losses.
E horizon

9. R: An R layer is bedrock. When a soil
has direct contact with bedrock, especially
close to the soil surface, the bedrock
becomes a variable when developing land
use management plans and its presence is
noted in the soil profile description.
R layer

10. Processes of Soil Formation
In the course of soil formation the chemical composition of a soil-forming rock
changes. Some substances are carried (washed) out of its thickness, included into
(enveloped with) a soil formation, while others are accumulated.
In the course of soil formation, accumulation of a substance is accounted for by inflow of
organic substance
of plant and animal residues into a soil as well as from the hydrosphere (easily soluble
salts, gyps, carbonates of alkaline and alkali-earth metals, compounds of iron, earth
silicon, coming from groundwater) and the atmosphere (dust particles of different sizes
and composition, compounds, being contained in the atmospheric precipitation).
Outflow of substance from soil can take place with downward and lateral water flows in
the soil, removal of soil particles from its surface with water and wind flows.
A ratio between the substance accumulation and removal determines the balance of soil
formation.

11. On the Earth’s surface, a soil-forming process takes its course under the
influence of a great diversity of combinations of the soil-forming factors that
result in a diversity of the soil formation types and respective soils.
At the same time, the same processes are repeated in different soils, and they are
essentially of the same quality, but different by their intensities and in details of
their manifestation. As an example of such processes can be accumulation of
humus, occurring in all soils, though at different qualitative and quantitative
levels.
Such processes, common for different types of soil formation, are termed as
elementary soil-forming processes (ESP)

12. Biogenic-accumulative ESP. A group of processes, leading to accumulation of
organic (and other) substances in the upper part of a soil profile with direct
participation of organisms. This group includes such processes as forming of humus,
accumulation of forest litter (floor), peat formation and others.
Hydrogenic-accumulative ESP. Group of processes, leading to accumulation of
substances, coming to a soil profile from ground waters. This group includes such
processes, as salinization (accumulation of easily soluble salts), carbon enrichment
(carbonization) (accumulation of calcium carbonate at its deposition from mineralized
ground waters), metallization (hydrogenic accumulation of oxides and hydroxides of iron),
and others.
Elementary soil-forming processes (ESP

13. Metamorphic ESP. Group of processes of transformation of the soil minerals at a site,
i.e. without outflow or income of them from other parts of a soil profile. These are
such processes as siallitization (intrasoil weathering of minerals with formation of
secondary clay, represented by finely dispersed stratified aluminosilicates,
fersiallitization (a process of accumulation of oxides and hydroxides of iron against a
background of siallitization), gleization (a process of transformation of a mineral mass
under influence of regenerative situation, caused by long waterlogging of the soil),
and others.
Eluvial ESP. A group of processes of destruction or transformation of a soil material
with subsequent outflow (evacuation) of products of destruction or transformation
outside limits of an eluvial horizon. This group includes lixiviation (leaching)
(outflow of calcium carbonate or easily soluble salts with downward water flows),
podsolization (a partial destruction of soil minerals by acid soil solutions and
evacuation of products of this destruction with downward water flows), lessivage
(peptization and evacuation) of finely dispersed soil particles in their undestroyed
state with downward moisture, and others.

14. Illuvial-accumulative ESP. A group of processes of accumulation in the lower part of
a soil profile of a substance, evacuated (removed) from an eluvial horizon. This group
includes such processes as argillo-illuvial process (a process of illuvial accumulation
of silty particles, evacuated (removed) from an eluvial horizon at the lessivage), Al-
Fe-humus illuvial process (a process of illuvial accumulation of oxides and
hydroxides of iron and aluminum together with humus) and others.
Pedoturbative (ESP). A group of processes of intermixing of a soil
mass under the influence of different factors, i.e. both natural and anthropogenic.
Examples of processes from this group can be cryoturbation (a process of mechanic
unregulated movement (displacement) of soil masses at irregular freezing and melting
of the soil), and bioturbation (intermixing of soil by animals, inhabiting it).
Destructive ESP. A group of processes, leading to physical destruction of soil. In
particular, erosion (a process of destruction of oil due to action of running water or
wind) relates to such processes.