What is a Soil? | Types, Definition, Structure, Function & Facts

What is Soil?

Soil is the loose top layer of the Earth’s surface where plants grow. Soil is made up of a mixture of organic matter (decomposed plants and animals) and rock fragments and minerals.

How is Soil Formed?

Soil is formed over a long period of time by a number of factors. It can take up to 1000 years to form a centimeter of land. Besides time, other factors that help form soil include:

Living Organisms – This includes organisms such as plants, fungi, animals, and bacteria.

Topography – This is the topography or slope of the land surface where the soil forms.

Climate – The general climatic and weather conditions where the soil forms.

Parent Material – The parent material are minerals and rocks that slowly decompose to form soil.

Why is Soil Important?

At first, you might think that the floor is just dirt. Something you want to get rid of. However, soil plays a very important role in sustaining life on Earth.

Plants – Many plants need soil to grow. Plants use the soil not only to provide nutrients, but also as a means to attach themselves to the ground by their roots.

Atmosphere – Soil affects our atmosphere by releasing gases like carbon dioxide into the air.

Living organisms – Many animals, fungi and bacteria depend on soil as a place to live.

Nutrient cycles – Soil plays an important role in the nutrient cycle, including the carbon and nitrogen cycles.

Water – Soil helps filter and purify our water. soil properties

Properties of Soil

Soil is often described using a number of characteristics, including texture, structure, density, temperature, color, consistency, and porosity. One of the most important properties of soil is texture. Texture is a measure of whether a soil is more like sand, silt, or clay. The more the soil resembles sand, the less water it can hold. On the other hand, the more clay-like the soil, the more water it can hold.

Soil Horizons

Soil is made up of many layers. These layers are often referred to as horizons. Depending on the type of soil, there can be multiple layers. There are three main horizons (called A, B and C) present in all soils.

Organic – The organic layer (also called the humus layer) is a thick layer of dead vegetation such as leaves and twigs.

Topsoil – Topsoil is considered the “A” horizon. It is a fairly thin layer (5 to 10 inches thick) of organic matter and minerals. This layer is the main layer where plants and organisms live.

Subsoil – The soil layer below is considered the “B” horizon. This layer consists mainly of clay, iron and organic matter that has been accumulated through a process called alluvium.

Parent material – The parent material class is considered the “C” horizon. This layer is called the parent material because the upper layers are developed from this layer. It consists mainly of large rocks.

Bedrock – The bottom layer a few feet above the surface. The bedrock is made up of a large block of solid rock.

Interesting Facts about Soil Science

The process by which minerals move underground is called leaching.

In a teaspoon of good soil there will usually be several hundred million bacteria.

On average, an acre of well-cultivated land will support more than a million earthworms.

Soil is composed mainly of the elements oxygen, silicon, aluminum, iron and carbon.

It is possible to overuse the soil and remove so much of its nutrients and organic matter that plants will no longer be able to grow there.