Key Physical and Chemical Properties of Soil for Students
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
Very fine or very thin
Fine or thin
Medium
Coarse or thick
Very coarse or very thick.
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:
Terrace Farming
Soil Conservation Farming
Use of Green Manures
Salinity Management
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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FAQs on Properties of Soil: Structure, Types & Conservation
1. What are the main physical properties of soil that students should know?
The main physical properties of soil are its texture, structure, colour, water-holding capacity, and percolation rate. Soil texture refers to the size of the soil particles (sand, silt, or clay). Water-holding capacity is the ability of the soil to retain water, which is crucial for plant life. The percolation rate measures how quickly water passes through the soil.
2. What are the three main types of soil and their key characteristics?
The three main types of soil are sandy, clayey, and loamy. Their characteristics are:
- Sandy Soil: Contains large particles, feels gritty, has low water-holding capacity, and allows for good aeration.
- Clayey Soil: Contains very fine particles, feels sticky when wet, has high water-holding capacity, and has poor aeration.
- Loamy Soil: A balanced mix of sand, silt, and clay. It has good water-holding capacity, proper aeration, and is rich in humus, making it ideal for agriculture.
3. Why is loamy soil considered the most suitable for growing plants?
Loamy soil is considered the best for growing most plants because it combines the beneficial properties of sandy and clayey soils. It has a balanced texture that allows it to retain adequate water and nutrients for plant roots, while also providing enough air spaces for roots to breathe. Its rich humus content further enhances its fertility, making it the most productive soil for agriculture.
4. How does the water-holding capacity differ between sandy and clayey soils?
The water-holding capacity differs significantly due to particle size. Sandy soil, with its large particles and large air gaps, allows water to drain through very quickly, resulting in a low water-holding capacity. In contrast, clayey soil has very fine, tightly packed particles, which creates tiny pore spaces that trap and hold water effectively, giving it a high water-holding capacity.
5. What does the percolation rate of soil mean, and why is it important?
The percolation rate of soil is the speed at which water moves downward through the soil layers. It is usually measured in millilitres per minute (mL/min). This property is important because it determines how much water remains available for plants and how quickly an area might drain after rainfall. A very high percolation rate (like in sand) can lead to dry conditions, while a very low rate (like in clay) can cause waterlogging.
6. What are the key chemical properties of soil that affect plant growth?
The key chemical properties of soil that affect plant growth are its pH level (acidity or alkalinity) and its nutrient content. Most plants prefer a neutral pH (around 6.5 to 7.5). The soil must also contain essential nutrients like nitrogen, phosphorus, and potassium, which are vital for a plant's development, leaf growth, and fruit production.
7. What is a soil profile, and why is it important to understand its different layers?
A soil profile is a vertical cross-section of the soil from the surface down to the parent rock. It shows distinct layers called horizons. Understanding these layers (Topsoil, Subsoil, and Parent Rock) is important because each horizon has different properties. The topsoil (A-horizon) is rich in humus and nutrients, making it vital for plant growth. The composition of the lower layers affects drainage, root penetration, and the overall stability of the ground.
8. How does the process of weathering lead to soil formation?
Soil formation begins with weathering, which is the process of breaking down large rocks into smaller particles. This happens over thousands of years through physical forces (like wind, rain, and temperature changes) and chemical reactions. Once these rock particles are created, organic matter from decaying plants and animals (humus) mixes with them, gradually developing into fertile soil.
9. In what ways do living organisms, like earthworms, improve soil properties?
Living organisms play a crucial role in improving soil properties. Earthworms, often called 'nature's ploughs,' burrow through the soil, which improves its aeration and drainage. They also ingest soil and organic matter, and their castings enrich the soil with nutrients. Similarly, microbes like bacteria and fungi decompose dead organic matter, releasing essential nutrients and improving soil fertility and structure.
10. What is soil erosion and what are its main causes?
Soil erosion is the removal and transport of the top, most fertile layer of soil by natural agents like wind and water. The main causes of soil erosion are deforestation (cutting down trees, whose roots bind the soil), overgrazing by animals, and improper farming techniques. Strong winds can blow away loose, dry soil, while heavy rainfall can wash it away, leading to loss of fertility and land degradation.
