Soil

                                                  Soil

Soil is the most important layer of the earth’s crust. It is a valuable resource. Soil is the mixture of rock debris and organic materials which develop on the earth’s surface. The major factors affecting the formation of soil are relief, parent material, climate, vegetation and other life-forms and time. Besides these, human activities also influence it to a large extent. Components of the soil are mineral particles, humus, water and air. If we dig a pit on land and look at the soil, we find that it consists of three layers which are called horizons. ‘Horizon A’ is the topmost zone, where organic materials have got incorporated with the mineral matter, nutrients and water, which are necessary for the growth of plants. ‘Horizon B’ is a transition zone between the ‘horizon A’ and ‘horizon C’, and contains matter derived from below as well as from above. ‘Horizon C’ is composed of the loose parent material. This layer is the first stage in the soil formation process and eventually forms the above two layers. This arrangement of layers is known as the soil profile. Underneath these three horizons is the rock which is also known as the parent rock or the bedrock. In ancient times, soils used to be classified into two main groups – Urvara and Usara, which were fertile and sterile. In the 16^th century A.D., soils were classified on the basis of their inherent characteristics and external features such as texture, colour, slope of land and moisture content in the soil. . Based on texture, main soil types were identified as sandy, clayey, silty and loam, etc. On the basis of colour, they were red, yellow, black, etc. The National Bureau of Soil Survey and the Land Use Planning an Institute under the control of the Indian Council of Agricultural Research (ICAR) did a lot of studies on Indian soils. United States Department of Agriculture (USDA) Soil Taxonomy.

Soil types are classified according to many more factors. They are classified on the basis of colour, depth, pH, productivity, texture and process of formation.

Soil types according to depth are as follows:
1) Shallow Soil - Soil depth less than 22.5cm. Only shallow rooted crops are grown in such soil, e.g. Paddy, Nagli.
2) Medium deep soil - Soil depth is 22.5 to 45cm. Crops with medium deep roots are grown in this type of soil e.g. Sugar cane, Banana, Gram.
3) Deep soil - Soil depth is more than 45cm. Crops with long and deep roots are grown in this type a soil e.g. Mango, coconut

On the basis of genesis, colour, composition and location, the soils of India have been classified into:

(i) Alluvial soil

(ii) Black soil

(iii) Red and Yellow soil

(iv) Laterite soil

(v) Arid soil

(vi) Saline soil

(vii) Peaty soil

(viii) Forest soil.

 

Alluvial Soil

Alluvial soils are widespread in the northern plains and the river valleys. These soils cover about 40 per cent of the total area of the country. They are depositional soils, transported and deposited by rivers and streams. The alluvial soils vary in nature from sandy loam to clay. They are generally rich in potash but poor in phosphorous. In the Upper and Middle Ganga plain, two different types of alluvial soils have developed, viz. Khadar and Bhangar. Khadar is the new alluvium and is deposited by floods annually, which enriches the soil by depositing fine silts. Bhangar represents a system of older alluvium, deposited away from the flood plains. Both the Khadar and Bhangar soils contain calcareous concretions (Kankars). These soils are more loamy and clayey in the lower and middle Ganga plain and the Brahamaputra valley.                           

Black Soil

Black soil covers 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 western part of the Deccan Plateau, the black soil is very deep. These soils are also known as the ‘Regur Soil’ or the ‘Black Cotton Soil’. During the dry season, these soil develop wide cracks. Thus, there occurs a kind of ‘self ploughing’. Chemically, the black soils are rich in lime, iron, magnesia and alumina. They also contain potash. But they lack in phosphorous, nitrogen and organic matter. The colour of the soil ranges from deep black to grey.

Red and Yellow Soil

Red soil develops on crystalline igneous rocks in areas of low rainfall in the eastern and southern part of the Deccan Plateau. Along the piedmont zone of the Western Ghat, long stretch of area is occupied by red loamy soil. Yellow and red soils are also found 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 wide diffusion of iron in crystalline and metamorphic rocks. It looks yellow when it occurs in a hydrated form. The fine-grained red and yellow soils are normally fertile, whereas coarse-grained soils found in dry upland areas are poor in fertility. They are generally poor in nitrogen, phosphorous and humus.

Laterite Soil

Laterite has been derived from the Latin word ‘Later’ which means brick. The laterite soils develop in areas with high temperature and high rainfall. These are the result of intense leaching due to tropical rains. With rain, lime and silica are leached away, and soils rich in iron oxide and aluminium compound are left behind. These soils are poor in organic matter, nitrogen, phosphate and calcium, while iron oxide and potash are in excess. Hence, laterites are not suitable for cultivation; however, application of manures and fertilisers are required for making the soils fertile for cultivation. Red laterite soils in Tamil Nadu, Andhra Pradesh and Kerala are more suitable for tree crops like cashewnut. Laterite soils are widely cut as bricks for use in house construction. The laterite soils are commonly found in Karnataka, Kerala, Tamil Nadu, Madhya Pradesh and the hilly areas of Odisha and Assam.

Arid Soil       

Arid soils range from red to brown in colour. They are generally sandy in structure and saline in nature. In some areas, the salt content is so high that common salt is obtained by evaporating the saline water. Nitrogen is insufficient and the phosphate content is normal. Lower horizons of the soil are occupied by ‘kankar’ layers because of the increasing calcium content downwards. The ‘Kankar’ layer formation in the bottom horizons restricts the infiltration of water, and as such when irrigation is made available, the soil moisture is readily available for a sustainable plant growth. Arid soils are characteristically developed in western Rajasthan. These soils are poor and contain little humus and organic matter.

Saline Soil

They are also known as Usara soils. Saline soils contain a larger proportion of sodium, potassium and magnesium, and thus, they are infertile, and do not support any vegetative growth. Their structure ranges from sandy to loamy. They lack in nitrogen and calcium. Saline soils are more widespread in western Gujarat, deltas of the eastern coast and in Sunderban areas of West Bengal. . In the areas of intensive cultivation with excessive use of irrigation, especially in areas of green revolution, the fertile alluvial soils are becoming saline. Excessive irrigation with dry climatic conditions promotes capillary action, which results in the deposition of salt on the top layer of the soil. In such areas, especially in Punjab and Haryana, farmers are advised to add gypsum to solve the problem of salinity in the soil.

Peaty Soil

They are found in the areas of heavy rainfall and high humidity, where there is a good growth of vegetation. Organic matter in these soils may go even up to 40-50 per cent. These soils are normally heavy and black in colour. At many places, they are alkaline also. It occurs widely in 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 sufficient rainfall is available. The soils vary in structure and texture depending on the mountain environment where they are formed. In the snow-bound areas of the Himalayas, they experience denudation, and are acidic with low humus content. The soils found in the lower valleys are fertile.

SOIL DEGRADATION

Soil degradation can be defined as the decline in soil fertility. Soil degradation is the main factor leading to the depleting soil resource base in India. The degree of soil degradation varies from place to place according to the topography.

SOIL EROSION

The destruction of the soil cover is described as soil erosion. The soil forming processes and the erosional processes of running water and wind go on simultaneously. Wind and water are powerful agents of soil erosion because of their ability to remove soil and transport it. Regions with heavy rainfall and steep slopes, erosion by running water is more significant. Water erosion which is more serious and occurs extensively in different parts of India, takes place mainly in the form of sheet and gully erosion. Gullies deepen with rainfall, cut the agricultural lands into small fragments and make them unfit for cultivation. A region with a large number of deep gullies or ravines is called a badland topography. Ravines are widespread, in the Chambal basin. The country is losing about 8,000 hectares of land to ravines every year. Deforestation is one of the major causes of soil erosion. Plants keep soils bound in locks of roots, and thus, prevent erosion. They also add humus to the soil by shedding leaves and twigs. Forests have been denuded practically in most parts of India but their effects on soil erosion are more in hilly parts of the country. According to estimates, about half of the total land of India is under some degree of degradation. Every year, India loses millions of tonnes of soil and its nutrients to the agents of its degradation, which adversely affects our national productivity.

Soil Conservation

Soil conservation is a methodology to maintain soil fertility, prevent soil erosion and exhaustion, and improve the degraded condition of the soil. Soil erosion is essentially aggravated by faulty practices. The first step in any rational solution is to check open cultivable lands on slopes from farming. Lands with a slope gradient of 15 - 25 per cent should not be used for cultivation. Over-grazing and shifting cultivation in many parts of India have affected the natural cover of land and given rise to extensive erosion. It should be regulated and controlled by educating villagers about the consequences. Contour bunding, Contour terracing, regulated forestry, controlled grazing, cover cropping, mixed farming and crop rotation are some of the remedial measures which are often adopted to reduce soil erosion. Lands not suitable for cultivation should be converted into pastures for grazing. Experiments have been made to stabilise sand dunes in western Rajasthan by the Central Arid Zone Research Institute (CAZRI). The Central Soil Conservation Board, set up by the Government of India, has prepared a number of plans for soil conservation in different parts of the country. These plans are based on the climatic conditions, configuration of land and the 
social behaviour of people.
                                                   

Soil of India: Types, ph Range and Regional Distribution

Type	Features (formation, composition)	Distribution	Predominant Crops
Alluvial Soil pH range: 6.5-8.4	Two types: Khaddar- light in color, more siliceous in composition and composed of newer deposit Bhaggar- the older alluvium is composed of lime nodules and has clayey composition. It is dark in color.	Ganga and Brahmaputra river valleys ; deltas of Godavari and Krishna ; plains of Uttar Pradesh, Uttaranchal, Punjab, Haryana , West Bengal and Bihar ; Coastal strip of peninsular India	Rice , Wheat, Sugarcane, oil seeds
Desert Soil pH range: 7.6-8.4	Contain a high percentage of soluble salts but are poor in organic matter; rich enough in phosphate though poor in nitrogen	Rajasthan, Northern Gujarat and southern Punjab	Wheat, grams, melon, bajra (with irrigation)
Black Soil pH range: 6.5-8.4	The soils are derived from basalts of Deccan trap. They derive their name from their black color which may be owing to presence of titanium, iron. Consist of calcium and magnesium carbonates; high quantities of iron, aluminum, lime and magnesia and poor percentage of phosphate, nitrogen and organic matter	Maharashtra and Malwa plateaus , Kathiawar peninsula, Telengana and Rayalasema region of Andhra and northern part of Karnataka	Cotton , millets(include Jowar ,Bajra and ragi ), tobacco, sugarcane
Mixed Red and Black Soil pH range: 6.5-7.5		Scattered in Peninsular India	Millets, wheat
Red Soil pH range: below 5.5-7.5	Mainly formed due to decomposition of ancient crystalline rocks like granites and gneisses and from rock type rich in minerals such as iron and magnesium. Generally poor in nitrogen, phosphorus, humus but rich in potash. Siliceous and aluminous in nature. Clay fraction of the red soils generally consists of Kaolinitic minerals.	Eastern parts Deccan plateau, southern states of Kerala , Tamil Nadu and Karnataka and Chota Nagpur plateau (Jharkhand)	Wheat, Rice , Cotton , Sugarcane, pulses
Grey and Brown pH range: 7.6-above 8.5		Semi- arid tract of Rajasthan and Gujarat	Cotton, oilseeds
Laterite Soil pH range: below 5.5	Composed mainly of hydrated oxides of iron and aluminum; loss of silica from the soil profile	Assam hills, hill of summits of Kerala and Karnataka and eastern Ghats region of Orissa	Coffee, rubber, cashew nut, tapioca
Mountain soil pH range: 5.0-6.5		Coniferous forest belt of Jammu and Kashmir, Himachal Pradesh, Uttaranchal and Sikkim	Fruit, tea

          

Indian Soils with Percentage of Coverage

Soil Types	Percentage of Total Area
Alluvial soils	22.16
Black Soils	29.69
Red and yellow Soils	28.00
Laterite Soils	2.62
Arid Soils	6.13
Saline soils	1.29
Peaty and Organic Soils	2.17
Forest	7.94

                                                                                                                                                                                                                                                    
                                                                                                     By
                                                                                                      Vinay Kumar