Types of soil

Soil is a very broad term and one of the essential components of the environment. It usually refers to the Earth's loose layer that covers the surface of the planet. Soil properties may vary depending on the geological and climatic changes in different regions.

In this article, we are discussing the different types of soil. Before we discuss the different soil types, let us understand the definition of soil and how it is formed.

What is Soil?

Soil is an essential and outermost layer of the Earth's crust. It is a mixture of many substances, such as minerals, air, water, gas, organic matter, and other organisms. It is also the anchor for vegetation, which is the key to the food chain on Earth. The soil is made of rocks, and the entire formation process may take an average of 500 years or more.

Apart from this, soil quality is measured based on weathered rock particles and soil results. Healthy, high-quality soil is fertile and consists of a good soil structure. Also, healthy soil is biologically active. In most cases, the soil is primarily a combination of three different weathering rock particles, such as sand, silt and clay. The way they are all combined to form a soil defines the soil type and properties, such as how it holds water, how it feels touch, and how it is managed, etc.

How is soil formed?

The primary origin of soil is the depletion of mountains or rocks into small parts. The materials used for soil formation are known as 'parent material'. The soil basic properties and characteristics usually depend upon the type of parent material and the formation process. Besides, atmospheric conditions also play an important role in both the process and structure of the parent material's physical and chemical decomposition.

Generally, the soil formation begins with the explosion of rocks into the atmosphere. The process of soil formation can be divided into the following two stages:

Stage 1: Rocks break due to weathering. Weathering refers to a process where rocks are dissolved or broken into small pieces due to biological activities. It is usually divided into organic, mechanical, and chemical weathering processes.

Stage 2: Broken and small rocks move from one place to another and accumulate as sediment, forming soil. This happens due to erosion. Erosion refers to the process when broken rock particles are picked up and transported to other locations or surrounding areas with water, wind, ice, or gravity.

Types of Soil

There can be several soil types according to their size, shape, properties, atmosphere, and various organic and mineral compositions. However, the soil is mainly divided into the following four types:

Sandy Soil

Among all the different types of soil, sandy soil is known as the poorest type of soil. It consists of the largest soil particles, which can be seen with the naked eye. Because it is composed of the largest particles having huge gaps between them, it cannot hold on to water. This ultimately makes it tough for the plants' roots to absorb water. Besides, it has low nutrients. Therefore, plants don't get the proper nutrients and water in sandy soils because they are quickly carried away by the runoff. However, the sandy soil is considered good for the drainage system.

This type of soil is usually formed by the breakage or fragmentation of rock grain materials such as limestone, granite and quartz.

Characteristics of Sandy Soil

The following are the main characteristics of the sandy soil:

• Sandy soil includes the particles of rock and other hard minerals like silicon dioxide.
• The color of sandy soil is usually pale yellowish to yellowish-brown.
• Sandy soils are dry and feel gritty to the touch.
• The particle size in sandy soil generally lies between 0.075 mm to 2 mm:
  For fine sand - 0.075 mm to 0.425 mm
  For medium sand - 0.425 mm to 2 mm
  For coarse sand - 2 mm to 4.75 mm

Silt Soil

Silt soil or silty soil is composed of much smaller particles as compared to sandy soil. It is usually formed due to the composition of mud, clay, or small rocks deposited by a river or a lake. This type of soil is mostly seen nearest the river and lake. When moistened, the silt soil becomes a soapy slick. Also, if we roll it between our fingers, it generally leaves dirt particles on our skin.

Apart from this, silt soil is very smooth and can hold water comparatively better than sandy soil. However, Silt soil lacks nutrients compared to other types of soil. That is why it is known as fairly fertile. Silt soil is used in most farming practices to improve soil fertility. Because of its properties, the soil can easily be compacted by heavy overlying materials. Therefore, we need to be cautious while gardening; otherwise, it may get aerated poorly.

Characteristics of Silt Soil

The following are the main characteristics of the silt soil:

• Silt soil contains rock particles and other mineral particles collected by water during flooding on the valleys' floor.
• The color of silt soil is generally beige to black.
• Silt soil is usually very smooth to the touch and feels cold when wet.
• The particle size in silt soil lies between 0.002 mm to 0.05 mm.

Clay Soil

Among the other types of soils, clay soil consists of the smallest particles that are tightly packed. There can be very little to no air space between the particles. Clay is also defined as a fine-grained cohesive soil and has the finest particles among all other soil kinds. Due to tiny size particles, it has a tight hold on large quantities of nutrients and water. Because of its small particles, clay tends to settle itself. However, it allows only a small amount of air and moisture to pass through the spaces between particles.

Generally, clay soil feels cold, and it takes time to get warmed. It is because the water stored between particles also has to warm up. Besides, this type of soil can get too hard when it gets dry, especially in the summer. It becomes too difficult for the air and moisture to penetrate through its particles in such a case. This eventually makes clay soil tough for gardening. However, compost or mulch can be included in the soil to prevent certain soil freezing, making it ideal for planting. Apart from this, clay usually expands when it comes to contact with the water and shrinks when dry.

Characteristics of Clay Soil

The following are the main characteristics of the clay soil:

• Clay soil consists of microscopic and sub-microscopic particles compressed tightly with little or no air space. The particles of clay soil are usually derived from the chemical decomposition of rocks.
• The color of clay soil can vary from white to dull grey or brown to deep orange-red.
• The clay soil feels sticky and easily rolled when moistened. Besides, it becomes so rigid and compact when dried.
• Particle size in clay soils is usually measured at less than 0.002 mm.

Loamy Soil

The loamy soil or Loam is usually formed with a combination of clay, sand, and silt. That is why it includes the benefits of all these three soils. Some essential advantages of this type of soil are air circulation, different textures, better water retention, drainage, and fertility. Due to its advantages, this type of soil is known as agricultural soil. This soil eventually helps in holding water and plant food and allows air to pass through its particles down to the roots. Because of multiple benefits, loamy soil is considered one of the riches soil types for crop production.

Apart from this, loamy soil has higher pH levels, calcium, and good nutrients. Depending on the mixture's composition, loamy soil is referred to as either sandy or clay Loam or silt loam. A typical loam generally favors any single soil particle size over the two others. However, there are various ways to increase the soil's overall quality, such as adding soil inoculants, spraying leaves and soil with compost tea, or covering the soil with compost.

Characteristics of Loamy Soil

The following are the main characteristics of the loamy soil:

• The loam soil is a combination of sand, silt and clay, and the mineral composition is 40-40-20%, respectively.
• The color of loamy soil varies from grayish-brown to black.
• Clay soil feels soft, dry, and crumbly to touch.
• Loam soil is a mixture that includes sand having a particle size of more than 63 mm, silt having a particle size of more than 2 mm, and clay having a particle size of less than 2 mm.

Other Popular Types of Soil

The above-explained types of soil are the most common. However, there are many other types of soil. Some other popular types of soil include Peaty Soil, Chalky Soil and Saline Soil:

Peaty Soil

Peaty soil consists of a high amount of organic matter and is rich in water retention. Due to its high water retention property, it can be easily compressed. The color of peaty soil varies from dark brown to black. Peaty soil formation is evaluated 9,000 years ago with the rapid melting of the glaciers. This eventually caused the death of submerged plants by melting. Their decay occurred so slowly underwater that it caused an accumulation of organic area in a concentrated space. That is the reason that peaty soils have a large number of organic matter and water.

However, the soil can be drained to turn it into a good growing medium. Because of high water retention and good nutrient, peaty soil can keep plants healthy in dry months and protect their roots from damage during rainy months. Apart from this, the soil is saturated with acidic water, which can help control several plant diseases and utilize the pH-balance of other soil types.

Chalky Soil

Chalk soil is usually found in limestone beds or rocks and consists of deep-rooted chalk. This type of soil is extremely dry and inhibits the germination of plants. The color of the chalky soil is the same as the color of chalk. It also has the presence of calcium carbonate or calcite. The soil is not considered good for plants and gardening. It is too difficult to make it suitable for crop farming. It contains high lime materials and low amounts of water, which help provide a pH level of around 7.5. This makes chalky soil a general soil, and if used, it will give rise to yellow and flowering plants.

Saline Soil

The soil found in extremely dry areas is usually saline. It is called saline due to its high salt content. It can inhibit plant growth, inhibit germination, and cause difficulties in irrigation. This type of soil's salinity characteristic occurs due to the formation of soluble salts in the rhizosphere. High salt content affects plants' spread of water, which leads to dry stems in plants. It is easy to find if we are working on saline soil; we will probably notice a white layer of salts on the soil's ground surface. Besides, it also impacts the plants' growth. If plants have leaf tip burn, especially in young leaves, we are most probably using the saline soil.

Which soil is the best for gardening?

Loamy soil or Loam is considered the best choice for gardening and planting. It is best suitable for growing wheat, jute, pulses, cotton, oilseeds, sugarcane, and many other vegetables. It is also known for better water retention and sufficient nutrients required for plants' growth and development. Besides, sandy soil is beneficial for growing coconut and melon.