[Biology Class Notes] on What is Soil? Pdf for Exam

So, what is soil? About 70 % of the earth’s surface is covered with water, and the remaining is covered with soil. Here lies the importance of soil, which is a source of food and also residence. The earth layer, which is composed of soil and is influenced by soil formation, is called the pedosphere. Soil forms the principal substrata of life and is a reservoir of water and nutrients, also acting as a medium of filtration and breaking down harmful wastes. This shows the importance of soil and its role in the global ecosystem. The composition of soil includes organic matter, living organisms.

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Composition of Soil

The composition of soil varies from place to place, and hence when we answer the question of what is soil, other geographical factors also have to be taken into account. To describe the composition of the soil, we must understand that broadly speaking soil refers to any loose sediment, and the importance of soil becomes more prominent when we look at the types of soil. Clay soil, sandy soil, silt soil, and loamy soil are all different types of soil with different constituents and compositions. The composition of the soil is 45% minerals, 5% organic matter, and 50% empty spaces. The chemical composition of soil also varies. The importance of soil is that it provides a medium of growth for plants, provides a habitat for animals, and forms a crucial component of the biosphere.

Soil Formation

Soil is formed when the weathering of rocks takes place, and they break down into tiny pieces that form the soil. The various methods by which soil is formed include mechanical weathering, chemical weathering, and biological weathering. So, when we describe the composition of the soil, we must take into account how the soil has been formed. In mechanical weathering, the rocks are broken down by physical weathering such as wind or running water, or temperature. Chemical weathering occurs when rocks are broken down with the help of chemical reactions, and this often ends up changing the chemical composition of the soil. Biological weathering takes place when organisms weaken and disintegrate rocks. For example, the roots of trees can penetrate the cracks of rocks and end up breaking the rock.

Constituents of Soil

Now that we know what the composition of the soil is let us take a look at the different constituents of soil. We already know the soil is made of 45% minerals, 20-30 % different gases, and 20-30% water. The soil is called a heterogenous body for this reason. The organic substances are found in very small amounts and depending upon the decomposition stage may be completely, partially, or undecomposed organic matter. Minerals are essential and are solid components made out of atoms. Minerals occur naturally with a fixed chemical structure. Gaseous compounds like Nitrogen and Oxygen are present in the pores of the soil and soil is generally rich in carbon dioxide which is released by the microorganisms. Water dissolves the various nutrients and minerals and transports them to different parts of the plant.

Importance of Soil

The soil is a very important substance for the survival of organisms. The fertile soil helps in the development and growth of plants which are not only a source of food but also life-sustaining oxygen. Various life forms like bacteria, algae, fungi, etc. are all supported by the soil which retains the moisture of the soil and helps in the decaying of dead organisms. Life is supported by the topsoil, which helps in reproduction, nesting, breeding, etc. of a few organisms. The fertility of the soil is also increased by the presence of various organic matter that helps in the growth of plants and the various minerals and elements present in soil help the plants to carry out various processes. This is the importance of soil.

Did You Know? 

The soil is used for making various things like cups, tiles, utensils, etc. The soil contents like gravel, clay, and sand are also used in the construction process of houses, roads, and buildings, etc. Useful mineral medicines like iron, calcium along with other things like petroleum jelly and cosmetics are also extracted from soil. Rainwater is absorbed by the soil, and the water seeps through and is stored as groundwater. The water is evaporated, and it is released into the air, which makes the atmosphere cooler and becomes a part of the water cycle. 

Solved Example

1. What is Soil? What Is Soil Made of?

Answer: Soil refers to a collection of loose sediments. The soil consists of 45% minerals, 20-30% different gases, 5% organic matter, and 20-30% water.