[Chemistry Class Notes] on Properties of Soil Pdf for Exam

It is a mixture of minerals, organic matter, liquids, gases, small organisms that altogether support life. It is the upper layer of the earth’s surface composed of a mixture of organic remains, clay, and rock materials on which plants grow. It supports plant life and growth. It continually undergoes development by numerous physical, chemical, and biological processes, which include weathering and erosion. The density of soil is 1.6 g/cm3.

Physical Properties of Soil

Physical properties of soil include colour, texture, structure, porosity, density, temperature, and air. The colours of soil vary widely from place to place and indicate some properties like organic matter, water, and redox conditions of the soil. Soil texture, structure, porosity, density, are related to the types of soil particles and their arrangement.

Soil Texture: Soil texture definition (such as loam, sandy loam, or clay) refers to the proportion of sand, silt, and clay-sized particles that make up the mineral fraction of the soil. Sand and silt are of no importance to the soil as they don’t contribute to the soil’s ability to restore water and nutrients. Clay is an active part of soil texture as it has a small size and has a large amount of surface area per unit mass and it helps in storing water and ions. The texture of soil helps to know about the amount of water that soil can hold, the rate of water movement through the soil, how workable and fertile the soil is.

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Absorption of Water:  Soil is able to absorb water because of its porosity. Water holding capacity is different for different types of soils. Sand absorbs less water than clay. Sandy soil water holding capacity is less than clay soil and loamy soil. Clay soil holds more water than sandy soil.

Soil Colour: Soils are of different colours (brown, yellow, red) depending on oxidised or ferric iron compounds. The darker the colour of the soil, the more organic content it contains. The red colour of the soil is due to the presence of iron oxide and The black colour soil is rich in minerals and humus.

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Soil Horizon

The soil is divided into different horizons from top to bottom:

• A-Horizon: The uppermost layer of soil is called topsoil. This layer mostly contains minerals from parent material with organic matter. A good material for plants and other organisms to live is found on this horizon.

• B-Horizon: This is the second layer from the top and is a little rich in humus and it supports moisture. This layer consists of clay, silt, nutrients, and weathered rocks. Minerals present in this layer are more in comparison to the top layer.

• C-Horizon: This is the third most layer from the top, and it consists of small pieces of rocks broken down due to weathering.

• Bedrock: This is the last layer of the soil and consists of layers of solid unweathered rock.

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The pH of Soil

Soil can be acidic, alkaline, or neutral. Some plants grow well in acidic soil such as potatoes. Plants like the bean, garlic grow well in the basic type of soil. Carrots and lettuce prefer neutral soil. The pH of soil under the chemical properties of soil. Other chemical properties include Calcium carbonate content, Soil sodicity, Soil nitrogen, etc.

Soil Structure Definition

Soil structure can be defined as the way individual particles of sand, silt, and clay are assembled together. Single particles when assembled appear as larger particles. These are called aggregates. Humus is a major deciding factor to know about the structure of soil because it causes the soil to become more porous and allows water and air to penetrate deep underground. 

Types of Soil Structure

What is Soil Conservation?

Soil conservation is the process of prevention of loss of the topmost layer of the soil from erosion or prevention of reduced fertility caused by over usage, acidification, salinization, or other chemical soil contamination.  By conserving soil we can preserve the fertility of the soil. Few methods of conserve them are: 

Formation of Soil

The formation of soil is a complex natural process. The uppermost layer of the earth crust is made up of soil. Soil contains minerals, organic matter and living organisms. The formation of soil takes place by breaking of rocks by physical and chemical agents.

There are three agents of soil formation which are as following :

• Mechanical Processes: The formation of soil when happens due to any of the mechanical forces, then these are called mechanical Processes. For example wind and rain.

• Chemical Processes: Chemical processes are those Processes in which rocks break due to chemical reactions.

• Biological Processes: Biological processes are those processes in which any biological change results in the formation of soil. For example the lichens present on the rocks a certain chemical which results in the formation of soil.

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