Soil Profile

The composition of different horizons in soil, from the surface vertically to where the land meets the rocks beneath, is called Soil Profile. In this article, we shall deal with the following:

• Soil Profile

• Kinds of soil

• How is soil formed

• Soil Moisture and its kinds

• Use of the soil moisture

• How to measure soil moisture

• Soil erosion

• Important questions

The uppermost layer is called soil. It is the first layer of Earth, which can be seen with our bare eyes. It is the most critical component of the growth of the plant. The soil consists of essential minerals. Soil is also important for agricultural purposes which are further required for food, clothing and shelter. Soil also provides shelter to small living organisms. Therefore, we can say that soil is an inseparable part of our lives. 

Soil Profile Definition 

The soil profile layers can be easily identified by the texture and color of the soil. The topmost layer of the Earth’s crust is the soil. It is the most critical layer which comprises various minerals that are organic along with rock particles. These layers of the Earth’s crust help to grow and support plants.

When the soil is formed, it gets settled in different vertical layers. Each layer has a different composition. They have different colours, textures and chemical compositions. These layers explain soil profile. 

Formation of Soil 

Soil is formed by the process of Weathering. Weathering is a phenomenon in which continuous physical and chemical breakdown of rocks takes place. This can be done by several agents such as wind, water or climate. The soil formed varies from one another because of the five major factors which are climate, parent rock, landscape, organisms and time. 

1. Parent Rock: Parent materials are those which bring forth the layers of soil. Since it is the foundational material, it influences the properties of the soil formed. For example, the parent rock of sandy soil is Lava Rock. This is why the sandy soil is in black colour. 

2. Climate: The amount of temperature and precipitation directly affect the rate of weathering of the parent rock. The soil that has more moisture will be highly weathered. More the moisture content, the more the movement of minerals in the soil. Warm temperatures also increase the amount of weathering. 

3. Time: Time plays an important factor in the formation of the soil. Soil takes thousands of years to form. The younger soil shares characteristics with the parent rock but with time, the soil ages and its properties differ from the parent rock. Therefore, with time, one type of soil can change to another. 

4. Landscape: The type of region where the soil grows also affects the type of soil. For example, water runs faster on the slope. Therefore, the amount of water present on the slope will be less than the amount of water present on the foot of the slope. This means the soil will be poor in the slopes and rich in the foot of the slope. 

5. Organisms: The organisms present in the soil also affect the nature of the soil. For instance, there are some organisms that help in the chemical reactions taking place inside the soil. This will directly lead to water infiltration. 

Different Types of Soil

These lead us to the various kinds of soil. The soil is divided into the following:

• Topsoil

• Subsoil

• Parent Rock

Layers of Soil

The soil scientists (also known as pedologists) have identified an exciting way to determine the soil profile model through the capital letters O, A, B, C, and E. All the above layers have unique and different characteristics from each other. 

Sometimes it is noted that this layer gets eroded due to various factors present in the environment like excess rain or wind can erode the top layer removing all minerals from the soil. 

The soil profile diagram shows the three major surfaces of the soil consisting of A, B, and C, which are the surface horizon, the subsoil, and the substratum. Again soil profile consists of an organic mineral coat at the surface (O). This surface provides the soil with all the natural minerals. 

1. O-Horizon: The O-Horizon soil has organic materials like dried leaves, small rocks, fallen trees, and other organic matter that can be decomposed. It has about 20 to 30 percent of organic matter in it. The colour of the soil is generally black brown and dark brown due to the existence of organic matter.

2. A-Horizon: The A-Horizon Layer consists of organic material and is famously called a humus layer. It is the uppermost layer of the soil that consists of dark decomposed matter, known as humus. Humus provides nutrients to the soil, therefore, making the soil more fertile. It also maintains the soil’s life. Since it increases soil’s water holding capacity, this layer is soft and can retain more water than any other layer. Many living organisms are present in this layer, for example, beetles, worms etc.

3. E-Horizon: The letter E denotes the master horizon, which is subsurface to all the layers of soil. It is present only in the forested regions. The colour of the soil is light. The letter E means eluviated horizon. The movement of the dissolved particles from the A- Horizon takes place here.

4. B-Horizon: B-Horizon is also known as subsoil because of its presence below the topsoil. It is the layer of soil that absorbs all the rainwater that flows through the topsoil. It accumulates the rain for further usage. It has humus but in lesser quantity than the A- horizon, organic matter, and soluble minerals. Since this layer contains large amounts of minerals, this layer is generally hard and compact.

5. C-Horizon: Another layer of soil that presents below the B-Horizon; this layer consists of less weathered rocks or parent rocks. It doesn’t contain any organic substance in it. It is also known as saprolite.

6. R-Horizon: R-Horizon is the layer that has partially weathered rocks or unweathered rocks. It is also known to be the foundation or the base layer of the soil. You can find manganese, granite, limestone, and basalt in this layer.

Types of Soil based on the Texture

The soil texture varies due to the presence of different sizes of rock particles. On the basis of the size particles, the soil can be classified into three types- Clayey soil, Loamy soil and Sandy soil.

Clayey Soil 

1. This type of soil has smaller and finer particles. 

2. Due to the presence of smaller particles, the particles are tightly packed leaving less room for air. 

3. Since there is no space for air, they can hold more water, thus making the soil heavy. 

4. This type of soil is most suitable for the growth of wheat and gram as this type of soil can retain large amounts of water.

Sandy Soil

1. This type of soil has heavy particles

2. Due to the presence of heavier particles, the particles are loosely packed leaving large spaces for air. 

3. Since there is a lot of space for the air to get filled, they are unable to hold water and the water gets easily drained. 

4. The type of soil is most suitable for the growth of cotton as the soil can hold plenty of air.

Loamy Soil 

1. This soil has both fine particles and large particles.

2. This type of soil can retain the right amount of air as well as water. 

3. This is the best soil for the growth of crops as it has the right water holding capacity and also humus present in it. 

What is Soil Moisture?

The water tenacity in the soil is called the soil moisture. The relevance of this coil moisture helps the plant extract the necessary minerals from the soil to grow. The soil absorbs water through various factors and also forms in the formation of the soil. When the water precipitates, it accumulates on the surface. The soil particles distributed on the surface helps to determine the porous nature of the soil. It helps in the vertical flow of the water to the regions below the surface. It is also called infiltration.

Types of Soil Moisture

The following are the various types of water present in the soil forming the Soil Moisture:

1. Gravitational Water: The free flow of water into the water table because of gravitational force is known as gravitational water. It is available for the plants to use as the water drains quickly if the soil is not compact. It can be found in the macropores of the soil.

2. Hygroscopic Water: Hygroscopic Water is soaked from the atmosphere to the soil and is held firmly. Plants cannot absorb water in large quantities, but they can still survive.

3. Chemically Combined Water: It is also known as combined water. After the removal of hygroscopic water because of the heat of the soil (150-degree Celsius), the remaining water changes its form into hydrated oxides of Iron, Silicon, etc.

4. Capillary Water: The water that is remaining on the soil after the free flow gets wholly drained out. The laws of capillary movement come into the picture and change its form into a film that surrounds the grains.

5. Atmospheric Humidity: Air carries a certain amount of water that is turned into vapour. It is measured in the form of vapour pressure or humidity. The ratio of vapour mass into the total mass of air derives from atmospheric humidity.

Importance of Soil Moisture

• Soil Moisture is useful as it contains essential nutrients which are necessary for the growth of plants. 

• It also helps in determining the yield of the crop in a particular region. 

• It aids in controlling soil temperature. 

• It also aids in soil formation. 

• The moisture of the soil also creates biological events of the microbes that are there in the soil. 

• The most important is that the Soil Moisture helps the plants during the process of photosynthesis. Photosynthesis is the phenomenon by which green plants prepare their own food with the help of chlorophyll and sunlight. 

How to measure Soil Moisture?

The soil moisture can be measured in the following manner:

1. Tensiometers: The Tensiometers measure the soil moisture’s tension. The tubes are filled with water with a porous ceramic tip added at the bottom. It is then sealed from the top that helps in creating a vacuum gauge. It is then put deep into the soil so that plants can absorb it quickly. The device is used to determine the availability of water percentage in the soil.

2. Electrical Resistance Blocks: These blocks contain two electrodes that are linked with lead wires. It is extended to the surface of the soil. The blocks of the porous material carry the electrodes. The purpose of the device is to measure the tension of the soil water.

3. Time Domain Reflectometry (TDR): If you want to determine the content of the soil moisture, TDR is the device that you must use. You can place the steel rods in the soil and pass electrical signals deep into the soil. If the signals return, you can measure the water content of the soil.

What is Soil Erosion?

The removal of the top layer of soil is called Soil erosion. The agents which contribute to the removal of soil are water, wind and ice. As the roots of the plant bind the soil firmly, when the plant is not there, the roots are not there to bind the soil and hence, the soil becomes loose. The soil is then easily removed by the agents. Soil erosion is most common in areas of less vegetation or zero vegetation. 

How to Prevent Soil Erosion?

The most significant way to prevent soil erosion is to minimize deforestation. Plant more trees so that the roots of the plant can bind the soil and prevent the soil from eroding.