Soil Formation – How Soil Is Formed?

Factors And Process

Cory NordinJune 7, 2020

The soil formation process has to start somewhere – whether it is from the erosion of rocks near
a body of water or the destructive effects of an environmental disaster. Different types of soil
have formed over millennia, and new types are likely to develop in the future, but how do they
form in the first place? What is the soil formation process? That is what we are here to discuss.

What Is Soil Formation?

Encyclopedia Britannica defines soil formation as “The evolution of soils and their properties.”
The next time you dig a hole in the ground or gander at the walls of dirt and rock cut away from
the sides of a highway, take a closer look. Visible layers show in the ground’s profile. These
layers are what tell the history behind the formation of that piece of soil.
Soil formation happens over hundreds, sometimes thousands, of years, but you can still see
evidence of that formation today. You can see the soft, dark topsoil layer and every layer
underneath, all the way down to the impenetrable bedrock. These layers are called soil horizons.
When viewing a soil profile, the horizons usually increase in age as they go down. The topsoil
can be just a few years or even a few months old, but the bedrock has been intact for
centuries. Deeper horizons usually remain unmoving until someone digs into the ground.
The soil horizons are O, A, E, B, C, and R.
Many factors go into soil formation, and how the soil turns out in appearance and feel depends
entirely upon them. Although the soil horizons do provide a lot of information regarding the
soil’s formation, visually, it will not provide as many details as a full mineral soil analysis
would.

Keep reading to learn about soil formation factors and how they change the soil.

Soil Formation Steps

Soil formation can vary depending on what type of soil is forming – clay, sand, or silt. But
generally, these are the three stages that most soils go through on their way to full formation.

1. Erode – Elements of weather cause the rocks, soil, and plant matter in an area to
erode and become sediment that contains various minerals and nutrients that were
in the previous materials.
2. Harden – The minerals harden over time to form deposits within the ground –
these will later combine with other elements to create the final soil.
3. Combine – After humans, animals, or environmental events cause the mineral
deposits in the ground to become loose, they combine with organic matter in
upper layers of the Earth and build until the soil forms.
 Factors Affecting Soil Formation

There are many factors in nature that influence soil formation. These factors determine what type
of soil forms (sandy, loam, red clay…etc.) and its location in the world after formation.

The first and most important factor affecting soil formation is the parent material. After that,
various things can change the formation process, but each factor can have an impact on the final
product.

Parent Material

All soil types start with parent material. The parent material can come from large rocks that
erode down to soft stone bits, which later form sandy or clay-composed soils, or it can come
from other elements in nature. Rock erosion is the most common parent material for soil, and
different types of rocks will form different variations of soil types.
Parent materials can come from a single area. However, most relocate from other areas by
moving through water, dragging in glacier ice till, or carry across plateaus by the wind.

The parent material becomes the base of a soil type and is responsible for the soil’s color,
texture, and mineral content.

Climate

The weather has a significant impact on soil formation. Water erodes rocks, wind transports
sand, and freezing temperatures can create permafrost. A climate is an area in which weather
patterns are consistent, and each climate can sway the soil formation process.

The weather in a climate can not only determine how the soil forms, but also govern whether
wild plants can grow fruitfully in the area.

As an example – Dry climates are 20°-35° North and South of the equator. They maintain very
little plant and animal life, and the weather is typically hot and dry for most of the year. The
effect this type of climate has on the local soil is low moisture content and minimal organic
matter in the soil’s composition.
Other climates, such as moist continental mid-latitude climates, allow many trees, plants, and
other vegetation to thrive for up to three seasons out of the year, resulting in a healthy soil loaded
with nutrients and natural compost.
Topography

Topography refers to the shape of the land. Topographic maps can include hills, valleys, and
plateaus, all of which affect the rate that certain minerals erode in the soil. For instance, a steep
hill can cause excess water flow and large boulders to fall, which would both lead to faster
erosion of parent materials.

Topographic features can also cause mineral deposits to form, which will lead to the natural
creation of soil.

Overall, topography is beneficial for not only soil formation but also for gardening herbs and
vegetables at home and agricultural research.
You can also look at the relationship between topography and the soil types. Many sand soil
deserts are in areas of flat plateaus, while colder climate areas with clay soils and permafrost
have mountains and valleys. This comparison shows just exactly how significant of an effect the
wind, weather patterns, and ground shape can have on soil formation.
Biological Factors

Humans and animals leave footprints wherever they go. They leave real footprints, but they also
leave an environmental footprint. When large mammals eat the grasses from the ground in fields,
scratch the bark off of trees with their antlers, and leave piles of excrement, they are contributing
to the formation of soil.

Animal droppings help to fertilize the soil, and any other movement that animals, insects, and
humans make when they travel compacts it into a more solidified form.

Microorganisms play an even greater role in soil formation because of how they guide the soil
nitrogen process, which is essential for the balance of minerals and chemical reactions in the soil.
Without the soil nitrogen process, the ocean and other bodies of water would become inhabitable
for sea life.
Time

Time allows the soil to complete its formation.

Although soil is continuously changing and forming, it needs an initial buffer time of a couple of
hundred years to develop into a soil the environment can use. During this time, organic matter
moves down through the layers of the ground, mineral deposits form, large rocks break down
into sand-like particles, and other nearby materials decompose to combine with the parent
material to form soil.

Types of Soil Formation

Clay, sand, and silt are the three textures of soil that mix to form all the different soil types.
Although the soil formation process is relatively the same for all three, some variations are
important to recognize.
Clay Soil Formation

Clay has a low water drainage rate and shallow air movement. These aspects come from the
soil’s structure. Clay soil has small clay particles that are no larger than 0.002 mm in diameter
and are grouped tightly. As a result of this type of particle structure, there is very little space left
over for air and water.

The particles in soil come directly from the soil formation process. Clay soil particles form from
a parent material that contains several minerals mixed together.

Minerals such as silicates, mica, iron, and aluminum hydrous oxide are the most common mix
that starts the clay formation process. These minerals join and harden over time and eventually
form a clay deposit.
Minerals can come from rocks that erode from strong water currents or harsh weather. Soil
erosion can contribute to this collection, as well.

Once the clay deposits form, they can combine with sand and silt in the ground to make soil.
Forces in nature, such as weather, are what combine them over time.
Sand Soil Formation

Sand formation happens as an effect of rock erosion. As stones, rocks, and boulders move down
streams and rivers, they become smaller and smaller as pieces chip away in water currents and
collisions with other rocks in the water.

Sand is composed of rock and some minerals. Different colors of sand can come from different
areas of the world and may contain an excess of certain minerals, such as the high iron content in
red sand—for instance, black sand forms from the erosion of the basalt rocks in volcanoes.

This sand then combines with clay and silt to form sandy soils. Other components of the soil can
include decaying plant and animal matter,

Silt Soil Formation

Silt forms similarly to clay and sand by the erosion of rocks and minerals. However, silt has a
slicker feel compared to sand and clay because of its uniquely shaped particles, which come from
mainly quartz and feldspar.

Soil Taxonomy

Soil taxonomy refers to the classification of soil types. Classification is necessary because of the
sheer number of soil types there are. All soils can break down into three types – clay, sand, and
silt – which combine to form the different variations of soils. Many elements also contribute to
soil formation.
Classifying soil types helps farmers when conducting a soil survey on their fields, or gardeners
when they wish to plant only the best species of plants that will thrive in the soil.

There are 12 soil orders in taxonomy.

Under these 12 orders are 64 suborders to classify and describe soils more precisely.

Soils that are within the same subgroup, or even in the same order for that matter, will be similar
in their physical and chemical properties like pH levels. Similarities in soil types indicate that the
soil formation process was somewhat similar or occurred in the same climate or location.
Soil Orders
 Alfisols
 Andisols
 Aridisols
 Entisols
 Gelisols
 Histosols
  Inceptisols
 Mollisols
 Oxisols
 Spodosols
 Ultisols
 Vertisol
Soil Maps

Soil maps are created from soil surveys. Soil scientists (pedologists) and farmers are the most
common people who might need a soil survey map. Soil maps can identify the limitations and
qualities of the soil in a large area of land. Landscapers can also utilize a soil survey map for
aeration purposes.

A soil survey map shows the results of a soil survey mapped out on a scaled-down version of a
plot of land. The ratio of these maps is usually 1:10,000 or 1:5,000. The base map is called a
cadastral map. Soil maps do not usually show a soil survey in its entirety but do give the specific
boundaries of differences in the soil.
The soil survey itself contains a slew of information on the major soil types in the survey area
and their characteristics, as well as aerial photographs and other specific data pertaining to
the physical and chemical properties of the soil.
Frequently Asked Questions

How long does it take for soil to form?

According to the United States Department of Agriculture (USDA), it can take at least 500 years
for one inch of topsoil to form. Although, many soil scientists say it takes even longer. To form
all the horizons in soil, it can take thousands, if not millions, of years.
Can soil be created?

Yes. Many gardeners use compost, moisture, much, and decomposing plants to create nutrient-
rich topsoil, though making a soil from scratch without a parent material may prove to be
difficult.

What is anthropogenic soil?

Anthropogenic soils are disturbed soils that have been modified by frequent human activity.

What does soil series mean?

A soil series describes a set of different types of soil that come from similar parent material.
Summary

Several factors and environmental influences can influence soil formation and the uses of the
soil. When looking at a soil survey map, it is important to realize the amount of time that is
behind the formation of that soil because it can make a difference when starting a field of crops.

7 PROCESSES INVOLVED IN SOIL FORMATION

Soil is defined as the uppermost surface layer of loose or unconsolidated materials which overlie
the crustal rock on which the plant grows.
Soil can also be defined as a mixture of minerals, organic matter, gases, liquids, and myriads
organisms.

The following are the processes that are involved in soil formation.
Organic accumulation.
This process involves the accumulation of decaying vegetables and animal matter on the ground
surface. The accumulated mass slowly breaks down to form humus which is a major component
of the soil.

Eluviation.
This is a mechanical wash down of fine mineral particles like those of clay from the upper layer
of the soil into the middle of lower layers.

The materials are moved in suspension by water which is percolating downward.

Eluviation can take place in the same layer when the water percolates horizontally.

The upper layer from which materials have been eluviated is called the eluvial zone

Leaching
This is the removal of soluble mineral matter in the solution from the upper horizon (layer) to the
lower horizon of soil.

This process can also be referred to as chemical eluviation.

It is common in wet climates. Leaching causes the topsoil to be deficient in minerals, especially
the bases because since they easily dissolve in water.
Illuviation.
This is the deposition or accumulation of materials that have been washed down from the upper
layer to the lower horizon of the soil through the process of eluviation.

Illuviaton sometimes leads to the formation of a hardpan or crust of laterite.

The materials deposited in the lower horizon include colloids, salts, and other mineral particles.

Colloids are very tiny particles of humus (organic colloids) and minerals especially clay.

They are so tiny that they cannot be seen using an ordinary optical microscope.

The tropical soils of the plateau north of Lake Victoria in East Africa are characterized by this
hardpan.

Precipitation.

This is the formation of solid matter in the subsoil.

The solid matter is formed from the solution washed down from the upper layers through
leaching. eluviation, leaching, illuviation, and precipitation take place at the same time and
within the same soil under the same climatic conditions.

Cheluviation.
This is the downward movement of materials in the soil which is very similar to leaching.
However, cheluviation occurs through the influence of organic agents which are also referred to
as chelating agents.a

The process involves plant acids rather than mere water as the case with leaching.

Organic sorting
This is the separation of materials, usually of different sizes, through organic influence.

It involves changes in sizes of soil particles, enrichment of the soil with organic matters such as
hummus, and movement of mineral elements in the solution that is leaching.

To sum up, soil formation involves seven processes which are organic accumulation, eluviation,
leaching, illuviation, precipitation, cheluviation, and organic sorting. All these processes are
related to each other.
Introduction
Soil is a mixture of organic matter, minerals, microbes, water, air and other
small living organisms. This soil is mainly formed from the process of rock
weathering.

In general, soil can be defined as a porous medium, developed in the

uppermost layer of Earth’s crust.

There are various types of soil that withstand several environmental stresses
or pressure including landslides, erosion, volcanoes, etc. Soil is mainly
classified by its proportions, texture and different forms of organic and
mineral compositions.

There are different types of soil, which are mainly classified based on their
properties, texture and their compositions. The four different types of soil
include- sandy soil, silt soil, clay soil and loamy soil.

What is Soil Taxonomy?

Taxonomy is a scientific process of classification based on their respective
properties. Similar to animals and plants, the soil is also classified into
different types based on its properties. The study of this soil classification is
termed soil taxonomy.

This system of soil classification is classified by the National Cooperative Soil

Survey of the United States and is mainly used for soil mapping. This
classification system comprises six categories or levels:

Order

Suborder

Great group

Subgroup

Family

Series
In the order level, there are ten classes of soils.

Gelisols

They are the permanently frozen soils, which are abundantly found at
extremely high elevations, including the Antarctic and Arctic regions. In
plants, this soil influences the downward movement of water and it
comprises about 10 to 12 per cent of the Earth’s glacier-free land surface.

Histosols

This soil mainly consists of organic matter in its upper portion and is mainly
formed by the decomposition of organic matter, dried leaves, twigs, grass
and mosses with the help of microbes present in the soil. This type of soil is
highly productive for farmlands.

Andisols

This soil is formed from the weathering of volcanic materials and holds a
huge quantity of both nutrients and water, hence making these soils very
productive and fertile.

Oxisols

This type of soil is abundantly found in tropical and subtropical regions. They
are the great deposits of iron oxides and quartz. This soil is not suitable for
gardens or other plantations as they are very poor in nutrients and have low
fertility.

Vertisols

This is a clay type of soil that has the capacity to shrink and swell.

Aridisols

This type of soil is formed from a mixture of salt, gypsum or carbonates.

They are abundantly found in both hot and cold deserts, which occupy about
10 to 12 per cent of the Earth’s glacier-free land area, including the dry
valleys of Antarctica. They are very low in fertility, and hence cannot be used
for plants.
Mollisols

These are the highly fertile soil with the deposition of calcium and
magnesium. This type of soil is found in grassland, therefore, also referred to
as grassland soil.

Alfisols

This type of soil is found under forest vegetation in a similar climatic region.
They are extended soil and occupy approximately 15 to 18 per cent of the
Earth’s glacier-free covering.

Entisols

It is the last and the lowest order in soil taxonomy with no soil development.
They are present on the topsoil horizon and occur in areas where deposition
is faster than the rate of soil development.