Formation and Types of Soils
The loose material or the upper layer of the mantle rock consisting mainly of very small particles and humus that can support the growth of plants is known as “soil”.
Soil mainly consists of mineral/rock particles, portions of decayed organic matter, soil water, soil air, and living organisms.
Soil is formed under specific natural conditions and each of the elements of the natural environment contributes to this complex process of soil formation known as “pedogenesis”.
The major factors that influence the formation of soil are
The fundamental factors that affect soil genesis can be categorized into five elements: climate, organisms, relief, parent material, and time.
As soil is formed it often has distinct layers, which are formally described as “horizons.”
The role of climate in soil development includes aspects of temperature and precipitation.
Temperature directly influences the speed of chemical reactions. The warmer the temperature, the faster reactions occur.
Animals, plants, and microorganisms all have important roles in soil development processes, in supplying organic matter, and/or in nutrient cycling.
Plant life provides organic matter to the soil and helps to recycle nutrients with uptake by roots in the subsurface.
Relief (Topography and Drainage)
The local landscape can have a surprisingly strong effect on the soils that form on site.
The local topography (relief) can have important microclimatic effects as well as affect rates of soil erosion.
In the northern hemisphere, south-facing slopes are exposed to more direct sunlight angles and are thus warmer and drier than north-facing slopes.
The parent material of soil is the material from which the soil has developed, whether it be river sands, shoreline deposits, glacial deposits, or various types of bedrock.
In youthful soils, the parent material has a clear connection to the soil type and has a significant influence.
The type of parent material may also affect the rapidity of soil development.
Parent materials also provide nutrients to plants and can affect soil internal drainage.
In general, soil profiles tend to become thicker (deeper), more developed, and more altered over time.
However, the rate of change is greater for soils in youthful stages of development.
The degree of soil alteration and deepening slows with time and at some point, after tens or hundreds of thousands of years, may approach an equilibrium condition where erosion and deepening (removals and additions) become balanced.
The Scientific Study of Soil can be called pedology and the Indian Institute of soil is located in Bhopal, Madya Pradesh.
In India, the Indian Council of Agricultural Research (ICAR) has classified soils into 8 categories. They are
Red & Yellow Soil
Mountainous or Forest Soil
Saline and Alkaline Soil
Arid or Desert Soil
Peaty and Marshy Soil
Alluvial soils are widespread in the northern plains and river valleys and cover 24% of the land.
It covers about 46% of the country’s total land area.
These soils are mainly derived from the debris brought down from the Himalayas.
They are rich in potash but poor in phosphorus.
Two different types of alluvial soils have developed in the Upper and Middle Ganga plains – Khadar and Bhangar.
Khadar is the new alluvium and occupies the flood plains of the rivers.
Khadar is enriched with fresh silt deposits every year.
Bhangar is the old alluvium, deposited away from the flood plains.
These soils are loamier and clay in the lower and middle Ganga plains and the Brahmaputra valley.
The major crops cultivated in Alluvial soils are– wheat, maize, sugarcane, pulses, oilseed, etc.
It accounts for about 3.7% of the total area of the country.
The name has been derived from the Latin word “later” which means brick.
These are typical soils of the monsoon climate which is characterized by seasonal rainfall. With heavy rain, lime and silica are leached away.
soil rich in iron oxide and aluminum are left leading to the formation of laterite soil.
Laterite soil is deficient in nitrogen, phosphate, and calcium; however, iron oxide and potash are in abundance.
It is a low fertility soil, but they respond well to manures and fertilizers.
Laterite soil is mainly found in the Western and Eastern Ghats. Especially in Karnataka, Kerala, Tamil Nadu, Odisha, Madhya Pradesh, and Assam.
Laterite soil hardens rapidly and irreversibly on exposure to the air, a property that leads to its use as building bricks.
The soil is most suitable for the plantation crops like coffee, Tea, Rubber, etc.
Black soil is also popular as “Regur Soil” or the “Black Cotton Soil”.
It covers about 14% of the country’s total land area.
It covers most of the Deccan Plateau – parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh, and some parts of Tamil Nadu.
In the northern parts of the Godavari and Krishna and the north-western part of the Deccan Plateau, the black soil is very deep.
The black soils are generally clay, deep and impermeable. They swell greatly and become sticky when wet in the rainy season. In the dry season, the moisture evaporates the soil shrinks and develops wide cracks.
Black soils are rich in iron, lime, aluminum, and magnesium and also contain potassium. However, these soils are deficient in nitrogen, phosphorus, and organic matter.
The Black Soil is more suitable for the crops like Cotton, pulses, millets, castor, tobacco, sugarcane, etc.
It covers about 18.5 % of the country’s total land area.
It is found in regions of low rainfall such as eastern and southern parts of the Deccan Plateau.
This soil is also present in parts of Odisha and Chhattisgarh and some parts of the Ganga Plain.
The red color is due to the presence of richness of iron in the Soil.
The soil appears yellow when it is in hydrated form.
The fine-grained red and yellow soil is usually fertile while the coarse-grained soil is less fertile.
This type of soil is generally deficient in nitrogen, phosphorus, and humus.
The major crops suitable in red soil are Wheat, cotton, oilseeds, millets, tobacco, pulses
Mountain Soil/Forest Soil
This type of soil is found in the forest and hilly regions where rainfall is sufficient.
The texture of the soil depends on the mountain environment.
These soils are coarse-grained on the upper slopes and loamy and silty on valley sides.
In the snowbound areas of the Himalayas, these soils undergo denudation and are acidic with low humus content. The soils found in the lower valleys are fertile.
Saline or Alkaline Soil
These soils are infertile due to the presence of high percentages of sodium, magnesium, and potassium. These soils are deficient in calcium and nitrogen.
The high salt content is mainly because of the dry climate and poor drainage.
These soils are found in arid and semi-arid areas.
These soils are mostly found in western Gujarat, deltas on the eastern coast, and Sundar ban areas of West Bengal.
In the Rann of Kutch, the south-western monsoon brings salt particles and deposits there as a crust. Seawater near deltas also increases the salinity of the soil.
It is also known as arid soil, and it accounts for over 4.32 % of the country’s total land area.
Desert soils are sandy to gravelly in texture and have low moisture content and low water-retaining capacity.
These soils are saline in nature and in certain regions the salt content is so high that common salt is obtained by evaporating water.
These soils are deficient in nitrogen.
Desert soils are profoundly found in western Rajasthan and contain little humus and organic matter
Peaty and Marshy Soils
These soils are found in regions of heavy rainfall and high humidity.
It supports the growth of vegetation.
Peaty soils are rich in humus and organic matter.
These soils are generally heavy and black. In many places, these soils are alkaline.
These are found in the northern part of Bihar, and the coastal areas of West Bengal, Odisha, and Tamil Nadu