LEARNING OBJECTIVE
This lesson will help you to: -
- learn about the composition of soil.
- know about different kinds of soil.
- learn about the fertility of soil.
- study the microorganisms present in soil.
Real Life Examples
- The leaves that fall down from the trees get mixed up in the top layer of the soil and within few days completely gets mixed with the soil. This forms the humus that makes the soil more nutrient rich.
- The soil found in the desert is poor soil because it lacks many essential nutrients and water. This is the reason why there are no plants except a few cacti in the deserts.
Amazing Facts
- 1 Tablespoon of soil has more organisms in it than there are people on earth.
- Soil scientists have identified over 70,000 kinds of soil in the United states.
- It takes 500 minimum years to from one inch of topsoil.
- soil stores 10 % of the world’s carbon dioxide emissions.
QUICK CONCEPT REVIEW
What is soil?
Soil is a natural body comprised of solids (minerals and organic matter), liquid and gases that occur on the land surface, occupies space, is made up of many layers and have the ability to support rooted plants in a nature environment.
What is soil made up of?
- Soil is a mixture of many things. It contains small pieces of broken rock, fallen leaves, dead critters decomposed tree branches, decayed plants etc.
- And because of the different materials and processes that affect its formation, soil comes in different colors and textures.
- Soil could have such lively colors as red, yellow and white but most of the time, soil is black, brown or grey.
- Due to the sand, silt, clay and other mineral particles in it, soil could be smooth, creamy, rough, crumbly) and sticky to touch.
- A typical healthy soil sample contains the following;
(a) 45% minerals
(b) 25% water
(c) 25% air
(d) 5% organic matter
- Soil also contains many organisms such as earthworm; and bacteria that help in maintaing the texture of the soil.
HOW IS SOIL FORMED?
- Soil formation is a slow process.
- Natural processes like weathering, erosions, rains, floods, hurricanes, thunderstorms, tornadoes, all contribute to soil formation. Lichen and plant roots also help in breakdown of rocks into little pieces to become part of the new soil.
Soil and its layers
- The layers of the soil are also called horizons.
- There are 4 layers of soil. At the top of these layers is humus.
- Humus: It is dark brown or black in color and is made up of rotten leaves and decayed bodies of plants and animals.
- Top soil: This layer is just below the humus. It is the most fertile layer and contains many microorganisms. It is rich in minerals. The plants grow in this layer.
- Subsoil: It is present below the top soil. This layer is home to earthworms and centipedes.
- Rock fragments: This layer is below subsoil and there is hardly any plant or animal life in this layer.
Hard Rock Layer: This layer is made of the big rocks and hence is called bedrock.
TYPES OF SOIL
There are 4 types of soil for e.g. Gravel, Sandy soil. Clay, Loam.
Gravel: (Only Rocks) do not hold Water.
Sandy soil: Granular (Rocks + minerals)
Mostly found in deserts and beaches.
Clay: (Fine grain material) Rich in mineral but need fertilizers for cultivation. Smooth and soft.
One of the most important uses of clayey soil is in pottery.
Loam: (Sand + Silt + Clay) Ideal for agriculture, rich in humus.
Historical Preview
- The Earth’s soil has been developed over hundreds of millions of years, as the forces of weather have ground the top rocky layer of the Earth into smaller and finer grains, and as plant and animal life has helped to deposit nutrients.
- In 1950 there was more than half an acre of grain land for each person on earth.
Misconnect / Concept
Misconcept: Soils with adequate amounts of clay will not leak.
Concept: Not all clays are alike, and the arrangement of clay particles in a soil greatly influences permeability.
Misconcept: Soil is the precursor of rocks. It changes from soil to clay to rock.
Concept: It is the action of both physical and chemical weathering of the atmosphere wearing away the solid rock of the earth that, over long periods of time, create the smaller and finer sediments necessary for soil to develop.
Misconcept: Plants get their food from the soil.
Concept: Plants make their own food by the process of photosynthesis.
Misconcept: Soil of the rainforest is very fertile.
Concept: Only the top few inches of rainforest soil is very fertile. Minerals are found mainly in the forest plants, not the soil.
