Geography Class 11th Chapter 6: Soils PDF

CHAPTER SOILS H ave you ever thought about the most are called horizons. ‘Horizon A’ is the topmost important factor which supports trees, zone, where organic materials have...

CHAPTER SOILS H ave you ever thought about the most are called horizons. ‘Horizon A’ is the topmost important factor which supports trees, zone, where organic materials have got grasses, crops and numerous life- incorporated with the mineral matter, forms over the earth’s surface? Can one grow nutrients and water, which are necessary for a blade of grass without soil? While some the growth of plants. ‘Horizon B’ is a transition plants and organisms which are aquatic in zone between the ‘horizon A’ and ‘horizon C’, nature can sustain in water, do they not derive and contains matter derived from below as well nutrients from soil through water? You will as from above. It has some organic matter in realise that soil is the most important layer of it, although the mineral matter is noticeably the earth’s crust. It is a valuable resource. The weathered. ‘Horizon C’ is composed of the loose bulk of our food and much of our clothing is parent material. This layer is the first stage in derived from land-based crops that grow in the the soil formation process and eventually forms soil. The soil on which we depend so much for the above two layers. This arrangement of layers our day-to-day needs has evolved over is known as the soil profile. Underneath these thousands of years. The various agents of three horizons is the rock which is also known weathering and gradation have acted upon the as the parent rock or the bedrock. Soil, which parent rock material to produce a thin layer of is a complex and varied entity has always soil. drawn the attention of the scientists. In order Soil is the mixture of rock debris and to understand its importance, it is essential to organic materials which develop on the earth’s attempt a scientific study of the soil. surface. The major factors affecting the Classification of the soil is an effort to achieve formation of soil are relief, parent material, this objective. climate, vegetation and other life-forms and time. Besides these, human activities also CLASSIFICATION OF SOILS influence it to a large extent. Components of the soil are mineral particles, humus, water and India has varied relief features, landforms, air. The actual amount of each of these depend climatic realms and vegetation types. These upon the type of soil. Some soils are deficient have contributed in the development of various in one or more of these, while there are some types of soils in India. others that have varied combinations. In ancient times, soils used to be classified Have you ever dug a pit in the field of your into two main groups – Urvara and Usara, school to plant a tree while celebrating Van- which were fertile and sterile, respectively. In Mahotsava? Was the pit of uniform layer of soil the 16th centrury A.D., soils were classified on or did you notice different colours from the top the basis of their inherent characteristics and to the bottom of the pit? external features such as texture, colour, slope If we dig a pit on land and look at the soil, of land and moisture content in the soil. Based we find that it consists of three layers which on texture, main soil types were identified as  All India Soil & Land Use Survey (renamed as Soil & Land Use Survey of India) established in 1958 under Ministry of Agriculture SOILS 69 sandy, clayey, silty and loam, etc. On the basis about 40 per cent of the total area of the of colour, they were red, yellow, black, etc. country. They are depositional soils, Since Independence, scientific surveys of transported and deposited by rivers and soils have been conducted by various agencies. streams. Through a narrow corridor in Soil Survey of India, established in 1956, made Rajasthan, they extend into the plains of comprehensive studies of soils in selected areas Gujarat. In the Peninsular region, they are like in the Damodar Valley. The National found in deltas of the east coast and in the river Bureau of Soil Survey and the Land Use valleys. Planning an Institute under the control of the Indian Council of Agricultural Research (ICAR) did a lot of studies on Indian soils. In their effort to study soil and to make it comparable at the international level, the ICAR has classified the Indian soils on the basis of their nature and character as per the United States Department of Agriculture (USDA) Soil Taxonomy. ICAR has classified the soils of India into the following order as per the USDA soil taxonomy Sl. Order Area Percentage No. (in Thousand Hectares) Figure 6.1 : Alluvial Soil (i) Inceptisols 130372.90 39.74 The alluvial soils vary in nature from sandy (ii) Entisols 92131.71 28.08 loam to clay. They are generally rich in potash (iii) Alfisols 44448.68 13.55 but poor in phosphorous. In the Upper and (iv) Vertisols 27960.00 8.52 Middle Ganga plain, two different types of (v) Aridisols 14069.00 4.28 alluvial soils have developed, viz. Khadar and Bhangar. Khadar is the new alluvium and is (vi) Ultisols 8250.00 2.51 deposited by floods annually, which enriches (vi) Mollisols 1320.00 0.40 the soil by depositing fine silts. Bhangar (viii) Others 9503.10 2.92 represents a system of older alluvium, Total 100 deposited away from the flood plains. Both the Source : Soils of India, National Bureau of Soil Khadar and Bhangar soils contain calcareous Survey and Land Use Planning, Publication concretions (Kankars). These soils are more Number 94 loamy and clayey in the lower and middle Ganga plain and the Brahamaputra valley. The On the basis of genesis, colour, composition and location, the soils of India sand content decreases from the west to east. have been classified into: The colour of the alluvial soils varies from (i) Alluvial soils the light grey to ash grey. Its shades depend (ii) Black soils on the depth of the deposition, the texture of (iii) Red and Yellow soils the materials, and the time taken for attaining (iv) Laterite soils maturity. Alluvial soils are intensively (v) Arid soils cultivated. (vi) Saline soils (vii) Peaty soils Black Soil __ Vertisol (viii) Forest soils. Black soil covers most of the Deccan Plateau which includes parts of Maharashtra, Madhya Alluvial Soils Pradesh, Gujarat, Andhra Pradesh and some Alluvial soils are widespread in the northern parts of Tamil Nadu. In the upper reaches of plains and the river valleys. These soils cover the Godavari and the Krishna, and the north 70 INDIA : PHYSICAL ENVIRONMENT Figure 6.2 : Major Soil Types of India  -- Rich Rich in in -- Iron Iron oxide oxide && Aluminium Aluminium SOILS -- Poor Poor inin -- Lime Lime && Silica Silica 71 western part of the Deccan Plateau, the black Laterite Soil soil is very deep. These soils are also known as Laterite has been derived from the Latin word the ‘Regur Soil’ or the ‘Black Cotton Soil’. The ‘Later’ which means brick. The laterite soils black soils are generally clayey, deep and develop in areas with high temperature and impermeable. They swell and become sticky high rainfall. These are the result of intense when wet and shrink when dried. So, during leaching due to tropical rains. With rain, lime the dry season, these soil develop wide cracks. and silica are leached away, and soils rich in Thus, there occurs a kind of ‘self ploughing’. iron oxide and aluminium compound are left Because of this character of slow absorption behind. Humus content of the soil is removed and loss of moisture, the black soil retains the fast by bacteria that thrives well in high moisture for a very long time, which helps the temperature. These soils are poor in organic crops, especially, the rain fed ones, to sustain matter, nitrogen, phosphate and calcium, even during the dry season. 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. These soils have mainly developed in the higher areas of the Peninsular plateau. The laterite soils are commonly found in Karnataka, Kerala, Tamil Figure 6.3 : Black Soil During Dry Season Nadu, Madhya Pradesh and the hilly areas of Odisha and Assam. Chemically, the black soils are rich in lime, iron, magnesia and alumina. They also contain Arid Soils potash. But they lack in phosphorous, nitrogen and organic matter. The colour of the Arid soils range from red to brown in colour. soil ranges from deep black to grey. They are generally sandy in structure and saline in nature. In some areas, the salt content Red and Yellow Soil is so high that common salt is obtained by evaporating the saline water. Due to the dry Red soil develops on crystalline igneous rocks climate, high temperature and accelerated in areas of low rainfall in the eastern and evaporation, they lack moisture and humus. southern part of the Deccan Plateau. Along the Nitrogen is insufficient and the phosphate 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. Figure 6.4 : Arid Soil Along the piedmont zone of Western Ghat --> Red loamy soil Red & Yellow soil - Generally poor in nitrogen, phosphorous and humus.  72 INDIA : PHYSICAL ENVIRONMENT content is normal. Lower horizons of the soil soils are normally heavy and black in colour. are occupied by ‘kankar’ layers because of the At many places, they are alkaline also. It occurs increasing calcium content downwards. The widely in the northern part of Bihar, southern ‘Kankar’ layer formation in the bottom horizons part of Uttaranchal and the coastal areas of West restricts the infiltration of water, and as such Bengal, Orissa and Tamil Nadu. when irrigation is made available, the soil moisture is readily available for a sustainable Forest Soils -- Coarse-grained in the upper slopes Loamy & silty on valley sides plant growth. Arid soils are characteristically As the name suggests, forest soils are formed in developed in western Rajasthan, which exhibit the forest areas where sufficient rainfall is characteristic arid topography. These soils are available. The soils vary in structure and texture poor and contain little humus and organic depending on the mountain environment where matter. they are formed. They are loamy and silty on valley sides and coarse-grained in the upper Saline Soils - (Usara Soil) slopes. In the snow-bound areas of the They are also known as Usara soils. Saline soils Himalayas, they experience denudation, and contain a larger proportion of sodium, are acidic with low humus content. The soils potassium and magnesium, and thus, they are found in the lower valleys are fertile. infertile, and do not support any vegetative It is evident from the foregoing discussions growth. They have more salts, largely because that soils, their texture, quality and nature are Poor in of dry climate and poor drainage. They occur vital for the germination and growth of plant Nitrogen & in arid and semi-arid regions, and in and vegetation including crops. Soils are living Calcium waterlogged and swampy areas. Their systems. Like any other organism, they too structure ranges from sandy to loamy. They develop and decay, get degraded, respond to lack in nitrogen and calcium. Saline soils are proper treatment if administered in time. These more widespread in western Gujarat, deltas of have serious repercussions on other the eastern coast and in Sunderban areas of components of the system of which they West Bengal. In the Rann of Kuchchh, the themselves are important parts. Southwest Monsoon brings salt particles and deposits there as a crust. Seawater intrusions SOIL DEGRADATION in the deltas promote the occurrence of saline soils. In the areas of intensive cultivation with In a broad sense, soil degradation can be excessive use of irrigation, especially in areas defined as the decline in soil fertility, when the of green revolution, the fertile alluvial soils are nutritional status declines and depth of the soil becoming saline. Excessive irrigation with dry goes down due to erosion and misuse. Soil climatic conditions promotes capillary action, degradation is the main factor leading to the which results in the deposition of salt on the depleting soil resource base in India. The degree top layer of the soil. In such areas, especially of soil degradation varies from place to place in Punjab and Haryana, farmers are advised according to the topography, wind velocity and to add gypsum to solve the problem of salinity amount of the rainfall. in the soil. SOIL EROSION Peaty Soils The destruction of the soil cover is described as They are found in the areas of heavy rainfall soil erosion. The soil forming processes and the and high humidity, where there is a good erosional processes of running water and wind growth of vegetation. Thus, large quantity of go on simultaneously. But generally, there is a dead organic matter accumulates in these balance between these two processes. The rate areas, and this gives a rich humus and organic of removal of fine particles from the surface is content to the soil. Organic matter in these the same as the rate of addition of particles to soils may go even up to 40-50 per cent. These the soil layer. SOILS 73 Sometimes, such a balance is disturbed by Soil erosion is a serious problem for Indian natural or human factors, leading to a greater agriculture and its negative effects are seen in other rate of removal of soil. Human activities too are spheres also. Eroded materials are carried down responsible for soil erosion to a great extent. to rivers and they lower down their carrying As the human population increases, the capacity, and cause frequent floods and damage demand on the land also increases. Forest and to agricultural lands. other natural vegetation is removed for human Deforestation is one of the major causes of soil settlement, for cultivation, for grazing animals erosion. Plants keep soils bound in locks of roots, and for various other needs. and thus, prevent erosion. They also add humus Wind and water are powerful agents of soil to the soil by shedding leaves and twigs. Forests erosion because of their ability to remove soil have been denuded practically in most parts of and transport it. Wind erosion is significant in India but their effect on soil erosion are more in arid and semi-arid regions. In regions with hilly parts of the country. heavy rainfall and steep slopes, erosion by A fairly large area of arable land in the irrigated running water is more significant. Water zones of India is becoming saline because of over- erosion which is more serious and occurs irrigation. The salt lodged in the lower profiles of extensively in different parts of India, takes place the soil comes up to the surface and destroys its mainly in the form of sheet and gully erosion. fertility. Chemical fertilisers in the absence of Sheet erosion takes place on level lands after a organic manures are also harmful to the soil. heavy shower and the soil removal is not easily Unless the soil gets enough humus, chemicals noticeable. But it is harmful since it removes the harden it and reduce its fertility in the long run. finer and more fertile top soil. Gully erosion is This problem is common in all the command common on steep slopes. Gullies deepen with areas of the river valley projects, which were the rainfall, cut the agricultural lands into small first beneficiaries of the Green Revolution. fragments and make them unfit for cultivation. According to estimates, about half of the total land A region with a large number of deep gullies or of India is under some degree of degradation. ravines is called a badland topography. Ravines Every year, India loses millions of tonnes of are widespread, in the Chambal basin. Besides soil and its nutrients to the agents of its this, they are also found in Tamil Nadu and West degradation, which adversely affects our national Bengal. The country is losing about 8,000 productivity. So, it is imperative to initiate hectares of land to ravines every year. What types immediate steps to reclaim and conserve soils. are prone to gully erosion? Soil Conservation If soil erosion and exhaustion are caused by humans; by corollary, they can also be prevented by humans. Nature has its own laws of maintaining balance. Nature offers enough opportunities for humans to develop their economy without disturbing the ecological balance. 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 Figure 6.5 : Soil Erosion gradient of 15 - 25 per cent should not be used 74 INDIA : PHYSICAL ENVIRONMENT for cultivation. If at all the land is to be used be reduced by constructing a series of check for agriculture, terraces should carefully be dams. Special attention should be made to made. Over-grazing and shifting cultivation in control headward extension of gullies. This can many parts of India have affected the natural be done by gully plugging, terracing or by cover of land and given rise to extensive erosion. planting cover vegetation. It should be regulated and controlled by In arid and semi-arid areas, efforts should educating villagers about the consequences. be made to protect cultivable lands from Contour bunding, Contour terracing, encroachment by sand dunes through regulated forestry, controlled grazing, cover developing shelter belts of trees and cropping, mixed farming and crop rotation are agro-forestry. Lands not suitable for some of the remedial measures which are often cultivation should be converted into pastures adopted to reduce soil erosion. 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. Even these plans are fragmental in nature. Integrated land use planning, therefore, seems to be the best technique for proper soil conservation. Lands should be classified according to their Figure 6.6 : Terrace Farming capability; land use maps should be prepared Efforts should be made to prevent gully and lands should be put to right uses. The final erosion and control their formation. Finger responsibility for achieving the conservation of gullies can be eliminated by terracing. In land will rest on the people who operate on it bigger gullies, the erosive velocity of water may and receive the benefits. EXERCISES 1. Choose the right answer from the four alternatives given below. (i) Which one of the following is the most widespread and most productive category of soil? (a) Alluvial Soil (c) Black Soil (b) Laterite Soil (d) Forest Soil (ii) ‘Regur Soil’ is another name for the. (a) Saline Soil (c) Black Soil (b) Arid Soil (d) Laterite Soil (iii) Which one of the following is the main reason for the loss of the top soil in India? (a) Wind erosion (c) Excessive leaching (b) Water erosion (d) None of these - Rich in -- AI - Poor in -- L-S Rich in M-S-P