UNIT 3. THE ORIGIN AND COMPOSITION OF SOIL

Soil What is soil? Soil is the loose upper layer of the Earth's surface where plants grow. Soil consists of a mix of organic material (decayed plants and animals) and broken bits of rocks 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 for just an inch of soil to form. Besides time, other factors that help soil to form include: Living organisms - This includes organisms such as plants, fungi, animals, and bacteria. Topography - This is the relief or slope of the surface of land where the soil is forming. Climate - The overall climate and weather where the soil is forming. Parent material - The parent material is the minerals and rocks that are slowly disintegrating to form the soil. Why is soil important? At first you may think of soil as just dirt. Something you want to get rid of. However, soil plays a very important role in supporting life on Earth. Plants - Many plants need soil to grow. Plants use soil not only for nutrients, but also as a way to anchor themselves into the ground using their roots. Atmosphere - Soil impacts our atmosphere releasing gasses such as carbon dioxide into the air. Living organisms - Many animals, fungi, and bacteria rely on soil as a place to live. Nutrient cycles - Soil plays an important role in cycling nutrients including the carbon and nitrogen cycles. Water - The soil helps to filter and clean our water. Properties of Soil Soil is often described using several characteristics including texture, structure, density, temperature, color, consistency, and porosity. One of the most important properties of soil is the texture. Texture is a measure of whether the soil is more like sand, silt, or clay. The more like sand a soil is the less water it can hold. On the other hand, the more like clay a soil is, the more water it can hold. Soil Horizons Soil is made up of many layers. These layers are often called horizons. Depending on the type of soil there may be several layers. There are three main horizons (called A, B, and C) which are present in all soil. Organic - The organic layer (also called the humus layer) is a thick layer of plant remains such as leaves and twigs. Topsoil - Topsoil is considered the "A" horizon. It is a fairly thin layer (5 to 10 inches thick) composed of organic matter and minerals. This layer is the primary layer where plants and organisms live. Subsoil - Subsoil is considered the "B" horizon. This layer is made primarily of clay, iron, and organic matter which accumulated through a process called illuviation. Parent material - The parent material layer is considered the "C" horizon. This layer is called the parent material because the upper layers developed from this layer. It is made up mostly of large rocks. Bedrock - The bottom layer is several feet below the surface. The bedrock is made up of a large solid mass of rock. Interesting Facts about Soil Science The process by which minerals move down through soil is called leaching. In a teaspoon of good soil there will typically be several hundred million bacteria. The average acre of good cropland will be home to over 1 million earthworms. Soil is mostly made of the elements oxygen, silicon, aluminum, iron, and carbon. It is possible to over-farm soil and remove so much of its nutrients and organic matter that plants will no longer be able to grow in it.

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Soil What is soil? Soil is the loose upper layer of the Earth's surface where plants grow. Soil consists of a mix of organic material (decayed plants and animals) and broken bits of rocks 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 for just an inch of soil to form. Besides time, other factors that help soil to form include: Living organisms - This includes organisms such as plants, fungi, animals, and bacteria. Topography - This is the relief or slope of the surface of land where the soil is forming. Climate - The overall climate and weather where the soil is forming. Parent material - The parent material is the minerals and rocks that are slowly disintegrating to form the soil. Why is soil important? At first you may think of soil as just dirt. Something you want to get rid of. However, soil plays a very important role in supporting life on Earth. Plants - Many plants need soil to grow. Plants use soil not only for nutrients, but also as a way to anchor themselves into the ground using their roots. Atmosphere - Soil impacts our atmosphere releasing gasses such as carbon dioxide into the air. Living organisms - Many animals, fungi, and bacteria rely on soil as a place to live. Nutrient cycles - Soil plays an important role in cycling nutrients including the carbon and nitrogen cycles. Water - The soil helps to filter and clean our water. Properties of Soil Soil is often described using several characteristics including texture, structure, density, temperature, color, consistency, and porosity. One of the most important properties of soil is the texture. Texture is a measure of whether the soil is more like sand, silt, or clay. The more like sand a soil is the less water it can hold. On the other hand, the more like clay a soil is, the more water it can hold. Soil Horizons Soil is made up of many layers. These layers are often called horizons. Depending on the type of soil there may be several layers. There are three main horizons (called A, B, and C) which are present in all soil. Organic - The organic layer (also called the humus layer) is a thick layer of plant remains such as leaves and twigs. Topsoil - Topsoil is considered the "A" horizon. It is a fairly thin layer (5 to 10 inches thick) composed of organic matter and minerals. This layer is the primary layer where plants and organisms live. Subsoil - Subsoil is considered the "B" horizon. This layer is made primarily of clay, iron, and organic matter which accumulated through a process called illuviation. Parent material - The parent material layer is considered the "C" horizon. This layer is called the parent material because the upper layers developed from this layer. It is made up mostly of large rocks. Bedrock - The bottom layer is several feet below the surface. The bedrock is made up of a large solid mass of rock. Interesting Facts about Soil Science The process by which minerals move down through soil is called leaching. In a teaspoon of good soil there will typically be several hundred million bacteria. The average acre of good cropland will be home to over 1 million earthworms. Soil is mostly made of the elements oxygen, silicon, aluminum, iron, and carbon. It is possible to over-farm soil and remove so much of its nutrients and organic matter that plants will no longer be able to grow in it.

Read more at: http://www.ducksters.com/science/earth_science/soil_science.php
This text is Copyright © Ducksters. Do not use without permission.

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What is soil? Soil is the loose upper layer of the Earth's surface where plants grow. Soil consists of a mix of organic material (decayed plants and animals) and broken bits of rocks 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 for just an inch of soil to form. Besides time, other factors that help soil to form include: Living organisms - This includes organisms such as plants, fungi, animals, and bacteria. Topography - This is the relief or slope of the surface of land where the soil is forming. Climate - The overall climate and weather where the soil is forming. Parent material - The parent material is the minerals and rocks that are slowly disintegrating to form the soil. Why is soil important? At first you may think of soil as just dirt. Something you want to get rid of. However, soil plays a very important role in supporting life on Earth. Plants - Many plants need soil to grow. Plants use soil not only for nutrients, but also as a way to anchor themselves into the ground using their roots. Atmosphere - Soil impacts our atmosphere releasing gasses such as carbon dioxide into the air. Living organisms - Many animals, fungi, and bacteria rely on soil as a place to live. Nutrient cycles - Soil plays an important role in cycling nutrients including the carbon and nitrogen cycles. Water - The soil helps to filter and clean our water. Properties of Soil Soil is often described using several characteristics including texture, structure, density, temperature, color, consistency, and porosity. One of the most important properties of soil is the texture. Texture is a measure of whether the soil is more like sand, silt, or clay. The more like sand a soil is the less water it can hold. On the other hand, the more like clay a soil is, the more water it can hold. Soil Horizons Soil is made up of many layers. These layers are often called horizons. Depending on the type of soil there may be several layers. There are three main horizons (called A, B, and C) which are present in all soil. Organic - The organic layer (also called the humus layer) is a thick layer of plant remains such as leaves and twigs. Topsoil - Topsoil is considered the "A" horizon. It is a fairly thin layer (5 to 10 inches thick) composed of organic matter and minerals. This layer is the primary layer where plants and organisms live. Subsoil - Subsoil is considered the "B" horizon. This layer is made primarily of clay, iron, and organic matter which accumulated through a process called illuviation. Parent material - The parent material layer is considered the "C" horizon. This layer is called the parent material because the upper layers developed from this layer. It is made up mostly of large rocks. Bedrock - The bottom layer is several feet below the surface. The bedrock is made up of a large solid mass of rock. Interesting Facts about Soil Science The process by which minerals move down through soil is called leaching. In a teaspoon of good soil there will typically be several hundred million bacteria. The average acre of good cropland will be home to over 1 million earthworms. Soil is mostly made of the elements oxygen, silicon, aluminum, iron, and carbon. It is possible to over-farm soil and remove so much of its nutrients and organic matter that plants will no longer be able to grow in it. Activities Take a ten question quiz about this page.

Read more at: http://www.ducksters.com/science/earth_science/soil_science.php
This text is Copyright © Ducksters. Do not use without permission.

What is soil?
Soils are complex mixtures of minerals, water, air, organic matter, and countless organisms that are the decaying remains of once-living things. It forms at the surface of land – it is the “skin of the earth.” Soil is capable of supporting plant life and is vital to life on earth.

 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 an inch of soil.  Some factors that help soil to form are living organisms (plants, fungi, animals, bacteria), topography (the slope of the surface), the climate, parent material (mineral and rocks that are slowly desintegrating)





Watch this video to understand the process of weathering, essential in soil formation:

What functions does soil perform?
Soil performs many critical functions in almost any ecosystem (whether a farm, forest, prairie, marsh, or suburban watershed). There are seven general roles that soils play:

1. Soils serve as media for growth of all kinds of plants.
2. Soils modify the atmosphere by emitting and absorbing gases (carbon dioxide, methane, water vapor, and the like) and dust.
3. Soils provide habitat for animals that live in the soil (such as groundhogs and mice) to organisms (such as bacteria and fungi), that account for most of the living things on Earth.
4. Soils absorb, hold, release, alter, and purify most of the water in terrestrial systems.
5. Soils process recycled nutrients, including carbon, so that living things can use them over and over again.
6. Soils serve as engineering media for construction of foundations, roadbeds, dams and buildings, and preserve or destroy artifacts of human endeavors.
7.  Soils act as a living filter to clean water before it moves into an aquifer.

What are the different layers or "horizons" of soil?

There are different types of soil, each with its own set of characteristics. Dig down deep into any soil, and you’ll see that it is made of layers, or horizons (O, A, E, B, C, R). Put the horizons together, and they form a soil profile. Like a biography, each profile tells a story about the life of a soil. Most soils have three major horizons (A, B, C) and some have an organic horizon (O).

The horizons are:

O – (humus or organic) Mostly organic matter such as decomposing leaves. The O horizon is thin in some soils, thick in others, and not present at all in others.
A - (topsoil) Mostly minerals from parent material with organic matter incorporated. A good material for plants and other organisms to live.
E – (eluviated) Leached of clay, minerals, and organic matter, leaving a concentration of sand and silt particles of quartz or other resistant materials – missing in some soils but often found in older soils and forest soils.
B – (subsoil) Rich in minerals that leached (moved down) from the A or E horizons and accumulated here.
C – (parent material) The deposit at Earth’s surface from which the soil developed.
R – (bedrock) A mass of rock such as granite, basalt, quartzite, limestone or sandstone that forms the parent material for some soils – if the bedrock is close enough to the surface to weather. This is not soil and is located under the C horizon.

Watch this VIDEO . Revise the unit and pay attention to these facts about soil:

• Soil is a mix of mineral and organic material that sits below the Earth´s surface.
• There are many kinds of soil.
• Different types of soil have different colour, PH, particle size, permeability and water holding capacity.
• Soil provides a place for plants to grow. 
• Soil contains a lot of living and non-living materials: rocks, mineral, bacteria, animals, nutrients.
• It takes a very long time to make soil, sometimes thousand of years. 
• Soil is formed when rocks break down and mix with decaying organic materials like plants and animals. 
• This organic material provides food for plants. 
• There are five main factors that create soil: parent material, climate, biology, topography and time. 

Watch the second part of the video and aswer these 5 questions: 

-What is parent material?
-What is humus?
-Where does mineral material come from?
-How doe climate affect the soil?
-What happens if the climate is warm and moist?

GLOSARY

Loam (Spanish: loam)

1. soil that is made up of about equal parts of clay, sand and silt
2. has a crumbly texture that holds both air and water
3. is best for growing most types of plants

Clay (Spanish: arcilla)

1. natural earthy material that is stiff and sticky when wet. 

2. is used for making bricks, pottery, etc.

Soil Horizon (Spanish: horizontes del suelo o capas)

-a layer of soil that is different in color and texture from the layers above or below it.

Silt (Spanish: cieno, limo)

1. A mixture of fertile soil and tiny rocks that can make land ideal for farming

2. Mixture of humus, clay, and other minerals that forms the crumbly, topmost layer of soil.

Weathering: is the breakdown of rocks at the Earth’s surface, by the action of rainwater, extremes of temperature, and biological activity. It does not involve the removal of rock material.

There are three types of weathering, physical or mechanical, chemical and biological.

How is erosion different to weathering?

Erosion is the process by which soil and rock particles are worn away and moved elsewhere by wind, water or ice. Weathering involves no moving agent of transport.