Soil

Introduction

Soil is a material consists of five ingredients namely minerals, soil organic matter, living organisms, gas, and water.
Soil minerals are divided into three classes on the basis of the size. Such as - clay, silt, and sand.

Soil Profile

Leaching is loss of soluble substances and colloids from the top layer of soil by percolating Precipitation. 

'Horizon A' is the topmost layer, where organic materials along with the mineral matter, nutrients and water are present which are conducive for the growth of plants.

'Horizon B' is a transitional zone between the 'horizon A' and 'horizon C', and contains matter derived from below as well as from above.'Horizon C' is consists of the loose parent material. This forms the first stage in the soil formation process and subsequently forms the above two layers.This arrangement of layers is known as the soil profile. Beneath these three horizons is the presence of parent rock the bedrock.

Soil in India

India has different relief features, landforms, and vegetation types. These have resulted into the development of various types of soils in India.

In earlier times, soils used to be classified into two main groups — Urvara and Usara, which were fertile and sterile respectively.

Soils were classified on the basis of their inherent properties and external factors such as texture, colour, slope of land and moisture content in the soil.

On the basis of texture, main soil types were identified as sandy, clayey, silty and loam, etc. Based on colour, they are red, yellow, black, etc.Since Independence, scientific surveys of soils have been conducted by various agencies.

Soil Survey of India was established in 1956, which has made comprehensive studies of soils in selected areas like in the Damodar Valley.
On the basis of genesis, colour, composition and location, the soils of India have been classified into:

(i) Alluvial soils 

(ii)Black soils 

(iii) Red and Yellow soils

(iv)Laterite soils

(v)Arid soils

(vi)Saline soils 

(vii) Peaty soils
(viii)Forest soils

Alluvial soils

Alluvial soils is concentrated in the northern plains and the river valleys. These soils cover approx, 40 per cent of the total area of the country.

They are the result of deposition, transportation of sediments by rivers and streams.

The alluvial soils vary in nature from sandy loam to clay. They are mostly rich in potash but poor in phosphorous.In the Upper and Middle Ganga plain, two different kinds of alluvial soils have developed, viz. Khadar and Bhangar. Khadar is the new alluvium and is deposited by floods, which increases the fertility of the soil by depositin fine sediments.Bhangar represents a system of older alluvium, hence they are deposited away from the food plains.both the khadar and bhangar soil contain calcareous concretions(kankars). These soils are loamy and more clayey in the lower and middle ganga plain and the Brahmaputra valley.The soil contain decreases from the west to east. The colour of the alluvial soil varies from the light gray to ash grey. Due to their fertility, These soils are Intensively cultivated.

Black Soil

Black soil encompasses over most of the Deccan Plateau which includes parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh and some parts of Tamil Nadu.In the upper reaches of the Godavari and the Krishna, and the north Black Soil Black soil is located in most of the Deccan Plateau which includes parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh and some parts of Tamil Nadu.These soils are also called as the 'Regur soil' or the 'black cotton soil'. The black soil are generally clayey, deep and impermeable.They swell and become sticky when wet and shrink when dried. So, during the dry months, these soils develop wide cracks. Thus, there is a kind of 'self ploughing'.Due to this character of slow absorption and loss of moisture, the black soil retains the moisture for a long period of time that helps the crops, especially, the rain fed ones, to sustain even during the dry season.The black soils are rich in lime, iron, magnesia and alumina. They also have potash. But they lack in phosphorous, nitrogen and organic matter.

Red-Yellow Soil

It develops on crystalline igneous rocks in region of low rainfall in the eastern and southern part of the Deccan Plateau.

Yellow and red soils are concentrated in parts of Odisha and Chattisgarh and in the southern parts of the

middle Ganga plain.

The soil develops a reddish colour due to a presence of iron in crystalline and metamorphic rocks. It

looks yellow when it occurs in a hydrated form.

The fine-grained sediments of red and yellow soils are normally fertile, whereas coarse-grained soils

found in dry upland areas are poor in fertility. They are mostly poor in nitrogen, phosphorous and

humus.

Laterite Soil

Laterite has been derived from the Latin word 'Later' which means brick. The laterite soils are found in areas with high temperature and high rainfall. These are the result of intense leaching due to tropical rains.

These soils are poor in organic matter, nitrogen, phosphate and calcium, while iron oxide and potash are in excess.

Hence, laterite soils are not suitable for cultivation; however, application of manures and fertilisers are required to increase the soil's fertility.

Red laterite soils in Tamil Nadu, Andhra Pradesh and Kerala are more vital for tree crops like cashewnut. Laterite soils are widely used as bricks for use in house construction.

These soils have mainly developed in the higher areas of the Peninsular plateau. The laterite soils are concentrated in Karnataka, Kerala, Tamil Nadu, Madhya Pradesh and the hilly areas of Odisha and Assam.

Arid Soil

Arid soils varies from red to brown in colour. In some regions, the salt content is so high that common salt is obtained by evaporating the saline water.

Due to the dry weather conditions, high temperature coupled with increased evaporation, they lack moisture and humus.

Nitrogen is absent and lower horizons of the soil consists of 'kankar' layers because of the increasing calcium content downwards.

The 'Kankar' layer formation in the bottom horizons restricts the percolation of water, and as such when irrigation is made available, the soil moisture is available for a sustainable plant growth. found in western Rajasthan, which exhibit arid topography. These soils are poor and contain little humus and organic content.

Saline Soil

They are also known as Usara soils. Saline soils contain sodium, potassium and magnesium, and thus, they are infertile, and do not support any vegetative growth.

They have more salt content due to dry climate and poor drainage. They occur in arid and semiarid regions, and in waterlogged and swampy areas. The nitrogen and calcium are absent.

Saline soils are more prevalent in western Gujarat, deltas of the eastern coast and in Sunderban areas

of West Bengal. In the Rann of Kuchchh, the Southwest Monsoon brings salt particles and deposits

there as a crust.

Seawater intrusions leads to occurrence of saline soils. Excessive irrigation with dry climatic conditions promotes capillary action resulting into the deposition of salt on the top layer of the soil.

Peaty Soil

They are widely present in the areas of heavy rainfall and high humidity, where there is a good growth of vegetation. Thus, large quantity of dead organic content accumulates in these areas formimg rich humus and organic content to the soil.

It is concentrated over the northern part of Bihar, southern part of Uttaranchal and the coastal areas of West Bengal, Orissa and Tamil Nadu.

Forest Soil

As the name suggests, forest soils are formed in the forest areas where good amount of rainfall is available.

Soil Degradation

Soil degradation refers to the decline in soil fertility coupled with declining of the nutritional status due to erosion and misuse.