MECHANICAL MEASURES The mechanical or engineering methods most widely used include:
(a) excavation of different types of ditches and construction of terraces for the removal of excess of water from the fields.
(b) construction of dams for checking the erosive velocities of the water.
The main objectives are to increase the time of concentration by intercepting the runoff and thereby providing an oppottunity for the infiltration of water; and to divide a long slope into several short ones so as to reduce the velocity of the runoff and thus prevent erosion.
Basin Listing Small interrupted basins are made along the contour with a special implement called a basin lister. It helps to retain rain water as it falls and is specially effective on retentive soils having mild slopes.
Subsoiling It involves in breaking with a subsoiler the hard and impermeable subsoil to conserve more rain water by improving "the physical conditions of a soil. This operation does not involve soil inversion but promotes greater moisture penetration into the soil and reduces both runoff and soil erosion.
Contour Bunding It involves making a comparatively narrow-based embankment at intervals across the slope of the land on a level that is along the contour. It conserves soil and water in arid and semi-arid areas.
Graded Bunding or Channel Terraces This method is used in areas receiving rainfall of more than 80 cm per year irrespective of soil texture. It may be narrow or broad based. Generally in India the terraces are broad-based, that is, wide and low embankments constructed on the lower edge of the channel from which the soil is excavated.
Bench Terracing It consists of a series of platforms having suitable vertical drops along contours or on suitably graded lines across the general slope of the land. The vertical drop may vary from 60 to 180 cm, depending upon the slope and soil conditions.
Thursday, October 29, 2009
SOIL CONSERVATION
SOIL CONSERVATION
For prevention and control of soil erosion, two types of measures are undertaken: agronomic and mechanical.
AGRONOMIC MEASURES These include various methods of crop cultivation to ensure protection of the top soil. The idea is to help intercept raindrops and reduce the splash effect, obtain a better intake of water rate by the soil by improving the content of organic matter and soil structure, reduce the overland runoff through contour cultivation, mulches, dense growing crops, strip cropping and mixed cropping.
Contour Farming When the soil cannot absorb all the rain that falls on it then the excess water flows down the slope under the influence of gravity. If farming is done up and down the slope, the flow of water is accelerated as each furrow serves as a rill. Major part of the rain is drained away and the top fertile soil is washed off. All this results in a scanty and uneven growth of crops.
A simple practice of farming across the slope keeping the same level as far as possible has many beneficial effects. The ridges and rows of plants placed across the slope form a continual series oI-miniature barriers to the water moving over the soil surface. Their effect is great in reducing runoff, soil erosion and loss of plant nutrients.
Mulching Mulches prevent soil from blowing off and being washed away, reduce evaporation, increase infiltration to keep down weeds, improve soil structure and increase crop yields.
Strip Cropping It is another form of controlling the runoff erosion and thereby maintaining the fertility of soil. Strip cropping employs several good farming practices such as crop rotation, contour cultivation, stubble mulching and cover cropping. Strip cropping includes contour strip crop
ping, field strip cropping, wind strip cropping and permanent or temporary buffer cropping.
Contour strip 'cropping involves growing a soil-exposing and erosion-permitting crop in strips of suitable widths across the slopes on contour, z.lternating with strips of soilprotecting and erosion-resisting crops. It shortens the length of the slope, checks the movement of runoff water and helps to desilt it, and increases the absorption of rainwater by the soil.
Wind strip cropping consists of planting tall growing crops and low growing crops in alternately arranged straight and long but relatively narrow parallel strips, laid out light across the direction of the prevailing wind regardless of the contour.
In permanent buffer strip cropping, the strips are established to take care of the steep or highly-eroded slopes in fields under contour strip cropping. The strips are generally legumes, grasses or shrubs.
Mixed Cropping The important objectives of mixed cropping are a better and. continuous cover of the land, good protection against the beating action of the rain and good protection against soil erosion. The line sowing of mixed crops gives rise to the practice of intercropping.
For prevention and control of soil erosion, two types of measures are undertaken: agronomic and mechanical.
AGRONOMIC MEASURES These include various methods of crop cultivation to ensure protection of the top soil. The idea is to help intercept raindrops and reduce the splash effect, obtain a better intake of water rate by the soil by improving the content of organic matter and soil structure, reduce the overland runoff through contour cultivation, mulches, dense growing crops, strip cropping and mixed cropping.
Contour Farming When the soil cannot absorb all the rain that falls on it then the excess water flows down the slope under the influence of gravity. If farming is done up and down the slope, the flow of water is accelerated as each furrow serves as a rill. Major part of the rain is drained away and the top fertile soil is washed off. All this results in a scanty and uneven growth of crops.
A simple practice of farming across the slope keeping the same level as far as possible has many beneficial effects. The ridges and rows of plants placed across the slope form a continual series oI-miniature barriers to the water moving over the soil surface. Their effect is great in reducing runoff, soil erosion and loss of plant nutrients.
Mulching Mulches prevent soil from blowing off and being washed away, reduce evaporation, increase infiltration to keep down weeds, improve soil structure and increase crop yields.
Strip Cropping It is another form of controlling the runoff erosion and thereby maintaining the fertility of soil. Strip cropping employs several good farming practices such as crop rotation, contour cultivation, stubble mulching and cover cropping. Strip cropping includes contour strip crop
ping, field strip cropping, wind strip cropping and permanent or temporary buffer cropping.
Contour strip 'cropping involves growing a soil-exposing and erosion-permitting crop in strips of suitable widths across the slopes on contour, z.lternating with strips of soilprotecting and erosion-resisting crops. It shortens the length of the slope, checks the movement of runoff water and helps to desilt it, and increases the absorption of rainwater by the soil.
Wind strip cropping consists of planting tall growing crops and low growing crops in alternately arranged straight and long but relatively narrow parallel strips, laid out light across the direction of the prevailing wind regardless of the contour.
In permanent buffer strip cropping, the strips are established to take care of the steep or highly-eroded slopes in fields under contour strip cropping. The strips are generally legumes, grasses or shrubs.
Mixed Cropping The important objectives of mixed cropping are a better and. continuous cover of the land, good protection against the beating action of the rain and good protection against soil erosion. The line sowing of mixed crops gives rise to the practice of intercropping.
ZONES OF SOIL EROSION IN INDIA
ZONES OF SOIL EROSION IN INDIA It has been estimated by agricultural experts that yearly loss of soils in India due to water and wind erosions is to the tune of five billion tonnes. On the basis of major causes of soil erosion, the country has been divided into the following zones.
(i) North-eastern region (Assam, West Bengal, etc.) The main causes of soil erosion are heavy rains and floods and widespread bank-cutting.
(ii) Shiwalik ranges of the Himalayas The primary cause is destruction of vegetation. Flood in rivers due to heavy deposition of debris is another important cause. As a result of floods, sediments are deposited on fertile agricultural lands.
(iii) River banks (Yamuna, Chambal, Mahi, Sabarmati, etc.) A sizeable portion of agricultural land in Uttar Pradesh, Rajasthan, Gujarat and Madhya Pradesh has been transformed into ravines due to soil erosion.
(iv) Hills of South India (Nilgiris) The heavy soil erosion in the southern hills may be attributed to steep slopes, heavy rainfall and defective methods of cultivation.
(v) Arid regions of Rajasthan and South Punjab Some parts of Rajasthan and Punjab such as Kota, Bikaner, Bharatpur, Jaipur and Jodhpur are subject to soil erosion by wind action.
(i) North-eastern region (Assam, West Bengal, etc.) The main causes of soil erosion are heavy rains and floods and widespread bank-cutting.
(ii) Shiwalik ranges of the Himalayas The primary cause is destruction of vegetation. Flood in rivers due to heavy deposition of debris is another important cause. As a result of floods, sediments are deposited on fertile agricultural lands.
(iii) River banks (Yamuna, Chambal, Mahi, Sabarmati, etc.) A sizeable portion of agricultural land in Uttar Pradesh, Rajasthan, Gujarat and Madhya Pradesh has been transformed into ravines due to soil erosion.
(iv) Hills of South India (Nilgiris) The heavy soil erosion in the southern hills may be attributed to steep slopes, heavy rainfall and defective methods of cultivation.
(v) Arid regions of Rajasthan and South Punjab Some parts of Rajasthan and Punjab such as Kota, Bikaner, Bharatpur, Jaipur and Jodhpur are subject to soil erosion by wind action.
SOIL EROSION
Soil erosion is the wearing away and redistribution of the earth's soil layer. It is caused by the action of water, wind and ice, and also by improper methods of agriculture. If unchecked, soil erosion results in the formation of deserts. It has been estimated that 20 per cent of the world's cultivated topsoil was lost between 1950 and 1990.
If the rate of erosion exceeds the rate of soil formation (from rock), then the land will decline and eventually become infertile.
The removal of forests or other vegetation often leads to serious soil erosion because plant roots bind soil, and without them the soil is free to wash or blow away, as in the American dust bowl. The effect is worse on hillsides, and there has been devastating loss of soil where forests have been cleared from mountain sides, as in Madagascar. Improved agricultural practices such as contour ploughing are needed to combat soil erosion. Windbreaks, such as hedges or strips planted with coarse grass, are valuable, and organic farming can reduce soil erosion by as much as 75 per cent.
In India, severe soil erosion is a characteristic of areas with heavy rainfall and improper land management. Various types of erosion take place. Normal or geologic erosion is a slow, long process which ensures an equilibrium between soil removal and formation. Accelerated soil erosion is erosion of the soil surface due to animal or human interference at a rate faster than that involved in the soil's building up.
In arid and semi-arid parts with high wind velocity, wind is a major cause of erosion. Finer particles are generally carried farther than coarse particles are. Erosion by water is of three types. Sheet erosion is when rainfall pounds soil grains loose, carrying them downwards. As the huge sheet of water running downslopes gains acceleration, erosion of the soil underneath also takes place. When sheet erosion continues for long, the silt-laden runoff forms many finger-shaped grooves over a large area.
This is rill erosion. Again due to sheet erosion, concentration of water along depressed areas results in heavy erosion in these areas which is termed gully erosion. In hilly parts, heavy rainfall and earthquakes result in limdslides, which bring about slip or landslide erosion. When cobbles, silt and boulders get deposited on the torrent bed, the bed level of the torrent is raised. This reduces the transporting capacity of the torrent, causing erosion (stream-bank erosion).
If the rate of erosion exceeds the rate of soil formation (from rock), then the land will decline and eventually become infertile.
The removal of forests or other vegetation often leads to serious soil erosion because plant roots bind soil, and without them the soil is free to wash or blow away, as in the American dust bowl. The effect is worse on hillsides, and there has been devastating loss of soil where forests have been cleared from mountain sides, as in Madagascar. Improved agricultural practices such as contour ploughing are needed to combat soil erosion. Windbreaks, such as hedges or strips planted with coarse grass, are valuable, and organic farming can reduce soil erosion by as much as 75 per cent.
In India, severe soil erosion is a characteristic of areas with heavy rainfall and improper land management. Various types of erosion take place. Normal or geologic erosion is a slow, long process which ensures an equilibrium between soil removal and formation. Accelerated soil erosion is erosion of the soil surface due to animal or human interference at a rate faster than that involved in the soil's building up.
In arid and semi-arid parts with high wind velocity, wind is a major cause of erosion. Finer particles are generally carried farther than coarse particles are. Erosion by water is of three types. Sheet erosion is when rainfall pounds soil grains loose, carrying them downwards. As the huge sheet of water running downslopes gains acceleration, erosion of the soil underneath also takes place. When sheet erosion continues for long, the silt-laden runoff forms many finger-shaped grooves over a large area.
This is rill erosion. Again due to sheet erosion, concentration of water along depressed areas results in heavy erosion in these areas which is termed gully erosion. In hilly parts, heavy rainfall and earthquakes result in limdslides, which bring about slip or landslide erosion. When cobbles, silt and boulders get deposited on the torrent bed, the bed level of the torrent is raised. This reduces the transporting capacity of the torrent, causing erosion (stream-bank erosion).
Desert Soils, Saline and Alkaline Soils, Peaty and Other Organic Soils'
Desert Soils Such soils prevalent between the Indus and the Aravallis (in Punjab and Rajasthan) are covered under a mantle of blown sand. Some of the soils contain a high percentage of soluble salts but are poor in organic matter. They are rich enough in phosphate though poor in nitrogen.
Haryana, Rajasthan and Punjab have land covered with such soils. In all, they cover about 1.42 lakh sq km of land surface.
A number of crops can be cultivated. These soils in many parts of Rajasthan, for instance, have emerged suitable for growth of cotton and cereals. .
Saline and Alkaline Soils These salt-impregnated and infertile soils, also known as reh, usar and kallar, form an important soil group. Salts that make up saline soils include free sodium and those that compose alkali soils include sodium chloride. These soils have undecomposed mineral fragments that on weathering produce magnesium, sodium and calcium salts.
Spread across arid and semi-arid northern India such as parts of Punjab, Uttar Pradesh, Haryana, Rajasthan and also Bihar, the saline and alkali soils cover a land surface of 170 lakh hectares.
Peaty and Other Organic Soils' Peaty soils with a high quantity of soluble salts and organic matter are found in parts of Kerala (Alleppey and Kottayam districts). They, however, lack potash and phosphate. Marshy salts, high in vegetable matter, are found in northern Bihar, coastal parts of O..rissa, Tamil Nadu and West Bengal and parts of Uttar Pradesh.
Haryana, Rajasthan and Punjab have land covered with such soils. In all, they cover about 1.42 lakh sq km of land surface.
A number of crops can be cultivated. These soils in many parts of Rajasthan, for instance, have emerged suitable for growth of cotton and cereals. .
Saline and Alkaline Soils These salt-impregnated and infertile soils, also known as reh, usar and kallar, form an important soil group. Salts that make up saline soils include free sodium and those that compose alkali soils include sodium chloride. These soils have undecomposed mineral fragments that on weathering produce magnesium, sodium and calcium salts.
Spread across arid and semi-arid northern India such as parts of Punjab, Uttar Pradesh, Haryana, Rajasthan and also Bihar, the saline and alkali soils cover a land surface of 170 lakh hectares.
Peaty and Other Organic Soils' Peaty soils with a high quantity of soluble salts and organic matter are found in parts of Kerala (Alleppey and Kottayam districts). They, however, lack potash and phosphate. Marshy salts, high in vegetable matter, are found in northern Bihar, coastal parts of O..rissa, Tamil Nadu and West Bengal and parts of Uttar Pradesh.
Laterite and Lateritic Soils, Forest Soils
Laterite and Lateritic Soils These soils possess a compact to vesicular mass in the sub-soil, composed mainly of hydrated oxides of iron and aluminium. Laterisation is said to be due to loss of silica from the soil profile in humid regions where the process of leaching is widespread. It is the in situ decay and decomposition of basalts and other aluminous rocks tmder warm, humid and monsoonic conditions which is thought to be responsible for forming
laterites of India. Lateritic soils are deficient in nitrogen.
They are chiefly found on the summits of hills of the Deccan, in Karnataka, Kerala, Madhya Pradesh, Orissa, Assam and the Malabars. They cover about 1.26 lakh sq km of land surface. Generally of low fertility, m<1ooring and other activities render them suitable for growing crops such as ragi, rice and sugarcane.
Forest Soils Such soils are mostly found in forests and mountains and they occur along the slopes or in depressions and valleys in forested regions. Their mode of formation and character is controlled by geology, topography, climate, vegetation of the mountain ranges and other factors. Such soils have a high content of organic matter and nitrogen and generally show a great range in their chemical and mechanical composition. Forest soils are deficient in potash, phosphorus and lime. Fertilisation of these soils is a must for good yields.
Such soils are found in the Punjab, Himachal Pradesh, the Nilambur teak forests of Malabar, Jammu and Kashmir, Karnataka, Manipur, etc. Tea, coffee, tropical fruits and spices are obtained from plantations on these soils especially in south India. Wheat, maize, barley are cultivated in some states.
laterites of India. Lateritic soils are deficient in nitrogen.
They are chiefly found on the summits of hills of the Deccan, in Karnataka, Kerala, Madhya Pradesh, Orissa, Assam and the Malabars. They cover about 1.26 lakh sq km of land surface. Generally of low fertility, m<1ooring and other activities render them suitable for growing crops such as ragi, rice and sugarcane.
Forest Soils Such soils are mostly found in forests and mountains and they occur along the slopes or in depressions and valleys in forested regions. Their mode of formation and character is controlled by geology, topography, climate, vegetation of the mountain ranges and other factors. Such soils have a high content of organic matter and nitrogen and generally show a great range in their chemical and mechanical composition. Forest soils are deficient in potash, phosphorus and lime. Fertilisation of these soils is a must for good yields.
Such soils are found in the Punjab, Himachal Pradesh, the Nilambur teak forests of Malabar, Jammu and Kashmir, Karnataka, Manipur, etc. Tea, coffee, tropical fruits and spices are obtained from plantations on these soils especially in south India. Wheat, maize, barley are cultivated in some states.
Alluvial Soils
Alluvial Soils Essentially transformed soils, they form the most important and largest of all the soil groups. These soils, unlike those of the other types, have undergone very little pedogenic (soil formation) evolution since their deposition. The alluvium is of two types-the khadar and the bhanger. The khadar is light in colour, more siliceous in composition and composed of newer deposits while the bhanger or the older alluvium is composed of lime nodules (kankar) and has a clayey composition. It is dark in colour, Vertically, there is no clear differentiation between the alluvium types and the profile often lacks' stratification. Alluvial soils vary in different regions owing to factors like climate, vegetation and surface conditions. Alluvial soils are generally deficient in nitrogen and humus.
Alluvial soils are found throughout the plains of northern India. In the Indian Peninsula, they are confined mainly to the river deltas on the east coast, the lower valleys of the Narmada and the Tapti, northern Gujarat and Chhattisgarh plains, They occupy 7.71akh sq km or about 24 per cent of India's land area. The soils are suitable for the cultivation of cereals, pulses, oilseeds, cotton, sugarcane and vegetables. These favour jute cultivation in the eastern parts -of the Indian plains.
Alluvial soils are found throughout the plains of northern India. In the Indian Peninsula, they are confined mainly to the river deltas on the east coast, the lower valleys of the Narmada and the Tapti, northern Gujarat and Chhattisgarh plains, They occupy 7.71akh sq km or about 24 per cent of India's land area. The soils are suitable for the cultivation of cereals, pulses, oilseeds, cotton, sugarcane and vegetables. These favour jute cultivation in the eastern parts -of the Indian plains.
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