What is Soil?
Soil is an important layer of earth’s crust (outermost layer). It is the mixture of organic matter, minerals, gases, water and air and other organisms. It is the anchor for vegetation which is the key to a food cycle on Earth.
How is Soil Formed?
Soil originally comes from rocks, also called the ‘parent material’. Soil formation starts when rock is exposed to the atmosphere. Properties of a soil will depend upon the type of parent material and how the soil is formed. Atmospheric conditions play a vital role in both the process and rate of physical and chemical decomposition of the parent material.
Step 1: Rocks break due to weathering (rock sediments deposit at the site of destruction) and/or erosion (the broken rock materials transport to other locations).
Step 2: It transports through water, wind etc. and deposited in the form of sediments and produces soil.
Factors Affecting Formation of Soil
- Parent materials
Soil Horizon and Profile
Any soil is made of layers, also called horizons. Horizons put together, form a soil profile. Each profile tells a story about the life of the soil. There are generally six horizons that form the soil profile.
Minerals in Soil
There are two types of minerals present in the soil.
- Primary Minerals
Mainly silicate minerals with varying proportion of Aluminum, Calcium, Sodium, Iron and Magnesium)
- Secondary Minerals
Clay, Mineral Oxides etc.
Functions of Soil
Soil has four very important functions (apart from other usages)
- As a base/medium for plant growth (essential for life in our ecosystem)
- As a means of storage, supply and purification of water
- As a modifier of Earth’s atmosphere
- Providing natural habitat and basis for life.
Types of Soil in India
The soils of India has been classified depending on the how they are formed, their color, composition etc.
These soils cover more than 40% of the total land area of the country.
- Location: Mainly found in the northern plains and river valleys where the rivers deposit the sediments. In peninsular region, they are found in the coastal areas.
- Structure: Alluvial soils are rich in phosphoric acid and organic matter but poor in potash. Alluviums are mainly loams, i.e. mixtures of sand and clay.
- There are two types of alluvial soils:
- Khadar Soils: This type is moisture retentive and sticky when wet. It is new soil and is very fertile. Khadar areas are prone to flooding that become available for agriculture when a river changes its course.
- Bangar Soils: It is old soil and it is sandier and less fertile. Bangar areas are less prone to flooding.
- Major crops: If proper irrigation is done, the alluvial soils yield good crops of sugarcane, tobacco, cotton, rice, wheat, jute, maize, oilseeds, vegetables and fruits.
These soils are black in color and are also called ‘Regur’. These soils cover around 16% of the total land area of the country.
- Location: Black soils are generally found in Maharashtra, Madhya Pradesh, Gujrat, Andhra Pradesh and Tamil Nadu.
- Structure: These contain Lime, Potash, Magnesium, and Alumina but lack Phosphorous, Organic Matter etc. These are impermeable and develop wide cracks during dry season. This permits oxygenation of the soil to sufficient depths making it very fertile. They can also hold moisture very well.
- Major Crops: Black soils are rich in chemical properties and very suitable for growth of cotton. So, they are also called black cotton soil. Other major crops are wheat, jowar, linseed, sunflower and millets etc. Rice and sugarcane are also grown where proper irrigation facilities are available.
Red and Yellow Soil
Red in color due to wide diffusion of iron in igneous and metamorphic rocks. Yellow color forms due to hydration. These soils are formed where rainfall is low. These soils are sandier and cannot retain moisture for longtime.
- Location: Found in some parts of Deccan plateau, Odisha, Chhattisgarh, Western Ghats etc.
- Structure: They are rich in potash but lack lime, magnesium, humus etc.
- Major Crops: These soils are very fertile in nature. Red soils work well with the proper use of fertilizers and irrigation. It give excellent yields of cotton, tobacco, oil seeds, wheat, rice, pulses, millets, potatoes and fruits.
These soils are formed in the areas with high temperature and high rainfall. High temperatures facilitates the decomposition of humus by Bacteria while high rainfall leaches silica and lime. As a result these soils become acidic and rich in aluminum and iron oxides. Laterite soils do not retain moisture.
- Location: Found in Karnataka, Tamil Nadu, Kerala, Madhya Pradesh, Odisha, Assam etc.
- Structure: Poor in organic matter, nitrogen, phosphate and calcium. These are generally acidic in nature.
- Major Crops: This soil (not very fertile) is used in the cultivation of cotton, rice, wheat, pulses, tea, coffee, etc. This is also used in cashew-nut cultivation.
- There are types of Laterite Soils based on their particles:
- Deep Red Laterite: Have excess of iron oxide and potash but short of Kaolin (clay). Not fertile.
- White Laterite: The color is due to excess of Kaolin. These soils lose fertility very quickly.
- Underground Laterite: The upper parts are dissolved especially in iron which settles down below the upper layer. This makes the soils fertile.
- Other uses: It is useful for making bricks because of presence of huge amount of iron.
These soils are sandy and have low clay content. Due to high evaporation in arid regions, the soils become deficient of humus and moisture. However, proper irrigation results in fairly good crop yields. The color of this soil ranges from red to brown and light brown.
- Location: The region west of the Aravalli has arid soils.
- Structure: Saline in nature due to the high salt content. Poor in nitrogen but rich in plant food. Lack moisture and humus.
- Major Crops: Mainly drought resistant and salt tolerant crops such as barley, rape, cotton, wheat, millets, maize and pulses are grown.
Forest and Mountain Soils
This soil occupies about 9% of the total land area of India. These soils are formed by the deposition of organic matter derived from forest growth.
- Location: These soils are found mainly in Himalayan region, Western and Eastern Ghats as well as in some parts of the peninsular plateau.
- Structure: These soils are rich in humus but are deficient in potash, phosphorus and lime. Therefore, they need fertilizers for good yields.
- Major Crops: Good for plantations of tea, spices, coffee and tropical fruits in Karnataka, Tamil Nadu and Kerala and wheat, maize, barley and temperate fruits in Himachal Pradesh, J&K and Uttaranchal.
Saline and Alkaline Soils
These soils are known by different names such as Reh, Kallar, Usar, Thur, Rakar, Karl and Chopan.
- Structure: Some rock and mineral fragments liberate sodium, magnesium, calcium salts and sulfurous acid on weathering. These salts are transported by rivers and subsequently in to the lower soils. These salts are then transferred from lower layers to the top soil layer due to evaporation.
- Location: These soils are mainly found in AP and Karnataka. These are also found in drier parts of Bihar, Uttar Pradesh, Haryana, Punjab, Rajasthan and Maharashtra.
- Major Crops: Accumulation of the salts makes the soil infertile and renders it unfit for agriculture.
Peaty and Marshy Soils
Peaty and Marshy soils are formed in humid regions as a result of deposition of huge amounts of organic matter in the soils under waterlogged conditions. The peaty soils are black and heavy.
Peaty Soils: Highly salty and rich in organic matters. But, they are deficient in potash and phosphate. Mainly found in Kottayam and Alappuzha districts of Kerala where it is called Kari.
Marshy Soils: Result of water-logging and the presence of iron and varying amount of organic matter. These are found in the coastal areas of Orissa and Tamil Nadu, Sundarbans of West Bengal, in Bihar and Almora district of Uttaranchal.
Top crops: These soils are generally covered with water during the monsoon and they are used for rice cultivation as soon as the monsoon passes.
What is Soil Erosion?
Washing or blowing away of the top layer of the soil is called soil erosion. Top layer of soil is the most fertile because it contains the most organic, nutrient-rich materials. Soil erosion is caused by natural factors like rain, water, ice etc. or manual factors such as ploughing of the field. But it is also caused by man-made factors.
Common Man-Made Reasons for Soil Erosion
- Shifting cultivation
- Jhum cultivation etc.
Impact of Soil Erosion
- Reduces the capacity of soil to hold water.
- Lower layers generally contain fewer nutrients than top layer, hence, soil erosion contributes to loss of nutrients.
- Water infiltration is reduced, which makes it harder for the seedlings to break through the soil crust.
- Erosion does not remove topsoil uniformly over the surface of a field, which makes it impossible for a farmer to apply fertilizers and chemicals uniformly and obtain uniform results.
Soil Conservation is the effort to protect soil from erosion. The Government of India has set up the Central Soil Conservation Board to take care of this issue and make some plans to control soil erosion. Some measures that have been in practice to protect the soil erosion are:
- Checking overgrazing
- Changing agriculture practices