Soil Formation – How Soil Is Formed? Factors and Process

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.

soil formation

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

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

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

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.

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