Properties of Soil: Definition, Structure, and Soil Conservation

Soil is an important natural resource that aids in plant development and growth. You might have seen how many plants you come across are healthy and fresh while on the other hand some plants dry up quickly and wither away. So why does this happen? Why do some plants grow healthy while others die away? This growth and the health of plants mainly depend on the properties of the soil it grows in. Soil can be understood as the uppermost layer of Earth. This layer is a mixture of the materials of rock on which the growth of plants takes place, the organic remains, and clay. Soil is affected by various factors such as various physical, biological, and chemical processes that include erosion and weathering which strips the soil of its nutrients. These processes alter the properties of soil and therefore also impact the growth and health of plants. In this article, we will look at the various properties of soil.

Read More: Natural Resources Management

Keyterms: Soil, Plant, Natural resources, Earth, Clay, Gas, Living organisms, Water, Minerals, Slit soil, Clayey soil, Sandy soil

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What is soil?

Most of our land is covered by a loose surface material which is referred to as the soil. Soil is very important for plant growth as it provides structural support to plants for their growth while also supplying them with the water and the necessary nutrients required for their development. Soil is mainly composed of organic matter of the soil, gas, living organisms, water, and various minerals. Mainly soil can be classified into three types which are:

• Slit soil
• Clayey soil
• Sandy soil

The texture of the soil depends on the percentage of these particles present in it.

Soil

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Structure of Soil

The structure of soil mainly refers to the individual particles of clay, sand, and slit that assemble together to form soil. The larger particles are formed by combining these smaller particles that are also known as aggregates. The structure of the soil is majorly decided by the presence of humus. This is because humus is responsible for making the soil more porous which allows air and water to penetrate deep into the soil. The soil structure can be of various types such as:

• Very fine soil structure
• Fine structure of soil
• Medium structure of soil
• Thick structure of soil
• Very coarse structure of soil

Structure of Soil

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Properties of soil

The various physical properties of soil are its density, temperature, color, structure, texture, porosity, etc. 

1. Texture of soil

The texture of the soil, also called soil texture refers to the ratio of minerals and the relative amount of these particles that make up the soil. These separated minerals can be classified mainly as silt, sand, and clay. Slit and sand don't contribute anyhow to the ability of the soil to restore nutrients or water, hence, they are of no importance to the soil. An active part of the soil texture is clay as it has a larger amount of surface area per unit of mass and smaller size. Clay in the soil helps in storing water and ions. If there is more clay in the soil, the soil will be smooth in texture as clay has the smallest particle in soil. The particles of the slit are larger than the particles of clay so it isn't smooth. Sand particles are the largest in size in the soil. 

• Size of slit particles: 0.002 mm to 0.02 mm
• Size of sand particles > 0.02 mm

Different Types of Texture of Soil

2. Soil color

The soil varies in color from place to place. In some places, the soil may be brown, yellow, or even red. The color of the soil depends on the ferric or oxidized compounds of iron. The more organic content and remains are present in the soil, the darker is the color of the soil. The darker the color of the soil the higher is the temperature of the soil as the soil absorbs more heat due to the higher amount of organic content.

The colors of soil vary depending on the ferric compounds

3. Soil Horizon

The soil is divided vertically to classify it into different layers or horizons which are organized from top to bottom. These horizons are as follows:

• A-Horizon = The uppermost layer of soil is known as the A-Horizon. This is also known as the topsoil. This upper layer is rich in minerals and humus. This horizon is referred to as a home to many organisms that live inside the soil such as earthworms, snakes, etc. Compared to the other layers, this layer holds the most amount of water and also consists of clay, slit, and sand. 
• B-Horizon = From the top, the second vertical layer in the soil is known as the B-Horizon. As compared to the top layer, this layer is richer in minerals. This layer supports moisture and is rich in humus content a bit. This layer is comprised of clay, weathered rocks, slit, and some of the nutrients. 
• C-Horizon = This third layer of soil, also referred to as the C Horizon, is composed of broken pieces of rocks that are broken down into smaller parts due to processes of weathering.
• BedRock = This last layer of the soil, the bedRock, is composed of various layers of solid rocks that are unweathered.

Different Horizons of Soil

4. Percolation rate/Porosity/Water absorption

Water is absorbed in the soil due to the porosity of the soil. Different types of soils have varying capacities for holding and retaining water. Sand soil has lesser water capacity than clay soil therefore it absorbs less water while clay soil retains and absorbs more water than sandy soil.

Water retention in Sandy soil < Water retention in Clay Soil

• Sandy soil allows the highest level of percolation of water through the soil as the sandy particles are really loose while clay soil has minimum percolation of water. 
• Rice Crops are grown in the field in standing water. Hence for the growth of paddy crops, soil with low percolation of water is the most ideal as the water is retained in the field for a longer duration of time.

5. Air in the soil

In between the particles of soil, there are certain spaces where the air is present. This air is required for respiration by the plants as it provides the plants with oxygen through their roots. 

As sand particles are larger, they can't fit together closely. Therefore, there is maximum space between sand particles. This space is filled with air. Clay particles on the other hand are packed together tightly so there is very little space for air to exist in between.

6. pH of soil

Many plants such as potatoes grow well in soil that is acidic in nature while garlic, beans grow well in the basic soil. Lettuces and carrots on the other hand grow healthy in soil that is neutral in nature. Hence, soil can be acidic, neutral, or alkaline (basic) in nature.

• Acidic: pH below 7
• Neutral pH: 7
• Alkaline: pH above 7

Read More: Importance of pH in Everyday life

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Soil Conservation

Many human activities have led to a degradation in the quality of the soil which has also led to soil pollution. One of the greatest causes of soil degradation is the erosion of soil wherein the top layer of soil is removed due to wind or water. But soils as we saw have a vital role in our ecosystem to ensure the survival of plants in our atmosphere. Hence, a need arises to keep a check on soil pollution while also adapting practices that promote the conservation of soil through its judicious use.

Soil Conservation refers to a technique or a practice that is followed to prevent the process of soil erosion. Soil erosion is mainly responsible for eroding or removing the topmost soil layer. This in turn removes all the nutrients and the organic matter that is necessary for the healthy growth of plants and aids in the production of fruits. We can help to conserve soil fertility by conserving the soil. This practice can be followed by various methods which can be practiced while agriculture and growing crops. Some of them are as follows:

• Contour Plowing
• Use of green manures
• Crop rotation
• Salinity management
• Terrace farming
• Windbreakers
• Perimeter runoff control
• Keyline design
• Streambank projections

Some methods or practices of soil conservation

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Things to Remember

• Soil is an important natural resource that aids in plant development and growth.
• Soil is mainly composed of organic matter of the soil, gas, living organisms, water, and various minerals.
• The texture of the soil, also called soil texture refers to the ratio of minerals and the relative amount of these particles that make up the soil.
• The color of the soil depends on the ferric or oxidized compounds of iron. 
• The more organic content and remains are present in the soil, the darker is the color of the soil. 
• The uppermost layer of soil is known as the A-Horizon and it is rich in minerals and humus.
• Water is absorbed in the soil due to the porosity of the soil.
• Soil erosion is mainly responsible for eroding or removing the topmost soil layer. This in turn removes all the nutrients and the organic matter that is necessary for the healthy growth of plants and aids in the production of fruits.
• Rice Crops are grown in the field in standing water, therefore, soil with a low rate of percolation of water is the most ideal as the water is retained in the field for a longer duration of time.

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