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India - vegetation, soils, forests - Part 1
1.0 DEFINITIONS OF SOIL
Soil is a natural body made up of solids (minerals and organic matter), liquid, and gases, that occurs on the land surface. It comprises of horizons or layers that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment. Some other definitions are
- The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants.
- The unconsolidated mineral or organic matter on the surface of the Earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro and micro-organisms, conditioned by relief, acting on parent material over a period of time. A product-soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics.
The upper limit of soil is the boundary between soil and air, shallow water, live plants, or plant materials that have not begun to decompose. Areas are not considered to have soil if the surface is permanently covered by water too deep (typically more than 2.5 meters) for the growth of rooted plants. The lower boundary that separates soil from the non-soil underneath is most difficult to define.
2.0 SOIL CHARACTERISTICS
Parent material: The parent material includes hard resistant and less resistant rocks. Granite, marble and slate are examples of hard resistant rocks whereas volcanic lavas and ashes, and the metamorphic (schist, gneiss) and sedimentary rocks (sandstone, clay, silt, and limestone) are examples of less resistant rocks. The term `rock' includes gravel, clay, and unconsolidated sand, loess, and alluvium which are less compact and less resistant soils.
Humus: Humus is the end product of breakdown of dead organic material. It is a structureless, dark-brown or black jelly found beneath or within the soil surface. The humus of ordinary soil is black, and is thus, responsible for making the top soil darker than the subsoil. It helps in the maintenance of soil fertility. The amount of humus in different soils varies considerably.
Soil Texture: The size of particles in the soil primarily charecterises it. Clayey soil is fine, sandy and coarse, while silt is an intermediate . The standard unit for the measurement of soil particles is the millimetre, but a smaller unit is the micron (1 micron = 0.001 mm), which is applicable, for instance, to the measurement of soil colloids. In sandy soil, the size of individual grains varies between 0.05 and 0.2 mm which are visible to the naked eye. The individual grains of clayey soil are 0.002 mm in diameter. Silty soil is finer than sand but coarser than clay. Its particles are found to have a diameter between 0.02 and 0.002 mm.
Soil Structure: Soil structure refers to the arrangement of soil particles. The way in which sand, silt, clay, and humus bond together to form beds is known as soil structure.
Soil Acidity: The pH value of a soil determines its acidity and alkalinity. The pH value is a scale that measures the concentration of hydrogen ion held by the soil colloids (particles). In pure water, one part in 10 million is dissociated to form hydrogen ions, i.e., 10-7 and the pH is thus 7; this is a neutral state on the scale of acidity. If a strong alkali such as caustic soda is dissolved in water, the solution is marked as alkaline (pH 14). By contrast, hydrochloric acid has a pH value of 3. A neutral soil has a pH value of about 7.2, and acid soil less than 7.2 (sometimes as low as 3). A strongly alkaline soil has a pH value of about 8 or higher.
Soil Air: The air in the soil helps in the process of oxidation which converts nitrogen into a form readily available to the plants. On the other hand, too high degree of oxidation (in the tropical regions) may consume so much organic material that the soil becomes increasingly sterile. Hence, the air content of the soil is vital both to the soil as well as organic life contained in it. Moreover, most bacteria, present in the soil in infinite numbers, require oxygen and are said to be aerobic. As these organisms are partly responsible for breaking down plant and animals remains, absence of air limits their activity.
Soil Water: The texture of the soil determines the amount of water that percolates downwards. The amount of water in the soil varies from nil in arid climates, which makes life virtually impossible for organisms, to a state of complete water-logging which excludes air, causes a reduction in bacteriological activity, and limits decomposition.
Soil Horizon: Soil horizon is a layer of soil which lies more or less parallel to the surface and has fairly distinctive soil properties.It differs chemically and/or physically from the layer below or above.
Soil Profile: It is a vertical series of soil horizons from the ground surface to the parent rock. The profile results from the same parent rock having similar horizons and soil profiles, but with varying characteristics according to their location .
3.0 TYPES OF SOILS IN INDIA
The soils of India can be classified on the basis of several criteria. The most acceptable classification is provided by the ICAR - The Indian Council of Agricultural Research. According to this classification Indian soils are divided into eight groups.
3.1 Alluvial Soil
From an agricultural point of view, alluvial soil is the most important among soils found in India. This soil covers about 24 per cent of India's land surface. These soils are composed of sediments deposited by rivers and the waves. They occupy the great plains from Punjab to Assam and also occur in the valleys of the Narmada and Tapti in Madhya Pradesh (MP) and Gujarat, the Mahanadi in Chhattisgarh and Odisha, the Godavari in Andhra Pradesh and the Kaveri in Tamil Nadu.
Geologically, the alluvium of the Great Plains is divided into khadar and bhangar, the former being new alluvium and the latter the old alluvium. This soil does not have recognizable horizons and in some portions it is covered by unproductive loess deposits. Alluvial soil is usually deficient in nitrogen and humus content and this necessitates repeated additions of manure and fertlisers to it. This soil is suitable for cultivation of all types of crops depending upon climatic suitability.
3.2 Black Soil
This is the second major group of soils found in India. Ideal for the cultivation of cotton crop due to its high moisture retention capacity, it is frequently referred to as black cotton soil and covers large tracts of the Deccan plateau. However, the crops like sugarcane, citrus fruits and banana also grow well on this type of soil. This soil is also classified as chernozem though locally it is known as regur soil. It covers large areas in Maharashtra, Gujarat, Madhya Pradesh, Karnataka, Andhra Pradesh and Tamil Nadu. The black colour is due to the presence of compounds of iron and aluminium. The soil is sticky when wet and develops wide cracks when dry. Its level of fertility is well accepted. Possessing high moisture retention capacity, black soil does not require much irrigation.
3.3 Red Soil
This is the third major soil group and covers the peninsular region reaching up to the Rajmahal Hills in the east, Jhansi in the north and Kutch Hills in the west. It surrounds the black soils on their east, southeast and north. It is generally porous and contains soluble salts and lime in small proportions. It is usually deficient in nitrogen, humus and phosphorous. Red soil is suitable for the cultivation of rice, ragi, tobacco and vegetables. Groundnuts and potatoes are grown at higher elevations.
3.4 Laterites and Lateritic Soil
These soils form the fourth group of Indian soils. Formed through the process of laterisation, they contain iron oxides which impart a red colour to the soil. The soil occurs in the higher reaches of the Sahyadris, Eastern Ghats, Rajmahal Hills and other higher areas in the peninsular region. It can also be found on the lower lands in parts of Maharashtra, Karnataka and in many parts of Kerala, as well as pockets of Odisha, West Bengal and Assam. Generally poor in humus, nitrogen and soluble salts due to heavy leaching, it is suitable for rice and ragi cultivation if manure is applied regularly.
3.5 Forest Soil
Forests and hilly areas are covered by forest soil, which is rich in organic matter but varies in character according to relief conditions. The Himalayas and other ranges in the north and the higher reaches of the hills in the south and the peninsular region have this soil. In some places it shows signs of podzolization. Forest soil is deficient in potash, phosphorous and lime, and needs continued use of fertilisers for good yields. Plantations of tea, coffee, spices and tropical fruits are laid out on such soils. (Podzolization - downward migration of Al and Fe, along with organic matter, from the surface areas & accumulation in deep areas)
3.6 Arid and Desert Soils
Soils belonging to this group are found in the northwestern parts of the country. It covers the entire area to the west of the Aravallis in Rajasthan and parts of Haryana, Punjab and Gujarat. It is rich in phosphates but poor in nitrogen and organic matter. Due to lack of water and their sandy texture soils of this group are considered poor. However, they prove quite fertile if irrigation facilities are provided and organic manure is regularly applied.
3.7 Saline and Alkaline Soils
Soils in many parts of the arid and semi-arid areas of Rajasthan, Punjab, Haryana, Uttar Pradesh and Bihar have saline and alkaline effervescences mainly of sodium, calcium and magnesium. These soils are called reh or kallar or usar and are infertile. However, the salts are usually confined to the upper layers and the soils can be reclaimed by improving drainage. Alkaline soils can be reclaimed by application of gypsum also.
3.8 Peaty and Other Organic Soils
Soils of this group contain high accumulations of organic matter and a considerable amount of soluble salts. Thus the soil is highly saline, rich in organic matter but deficient in phosphorous and potash. Peaty soil is found in Kottayam and Alleppey districts of Kerala. Marshy soils can be found in the coastal areas of Odisha, West Bengal and Tamil Nadu, central and northern Bihar, and Almora district in Uttarakhand. It is not conducive to cultivation.
3.9 Karewa soil
Karewas are the lacustrine deposits in the Valley of Kashmir and in Bhadarwah Valley of the Doda District of the Jammu Division. These are the flat topped mounds that border the Kashmir Valley on all sides. They are composed of fine silt, clay, sand, and bouldery-gravel. They are characterised with fossils of mammals and at places by peat. According to geologists, during the Pleistocene Period, the entire Valley of Kashmir was under water. Subsequently, due to endogenetic forces, the Baramullah Gorge was created and the lake was drained through this gorge. The deposits left in the process are known as karewas. The thickness of karewas is about 1400 m. In fact, the karewas have been elevated,dissected and in great measure removed by subaerial denudation as well as by the Jhelum river giving them the present position. The karewas are mainly devoted to the cultivation of saffron, almond, walnut, apple and orchards. The karewas, devoted to saffron cultivation are fetching good income to the growers. The karewas of Palmpur, Pulwama, and Kulgam are well known for their production of superior quality of saffron.
3.10 Snowfields
The area under snow and glaciers is about 4 million hectares. The high peaks of the Greater Himalayas, Karakoram, Ladakh, and Zaskar (Zanskar) are covered by ice and glaciers. The soils in these areas is immature, generally without soil erosion. It remains frozen and is unsuitable for the cultivation of crops.
4.0 PROBLEMS OF INDIAN SOILS
Soil degradation occurs due to natural factors as well as human activities, such as deforestation, over-grazing of animals and unscientific use of agricultural land.
Soil Erosion: Removal of the top soil is known as soil erosion. In the areas where rainfall is heavy water is the main agent of soil erosion, while in the arid and semi-arid areas wind is responsible for soil erosion. According to one estimate about 180 million hectare (about60 per cent of the total area of the country) is adversely affected by soil erosion.
The main agents of soil erosion are water, wind, sea-waves, glaciers, and shifting cultivation. Out of these, water is the most important agent of erosion. Water erosion may be classified under three categories:
- Surface erosion or the uniform removal of soil from the surface,
- Rill erosion in which the running water makes finger-shaped grooves in the land, and
- Gully formations, in which the rills are enlarged, making the land bad and unsuitable for cultivation. A typical example of gully erosion is provided in the Chambal valley in Madhya Pradesh. Rajasthan, and Uttar Pradesh also provide typical examples of gully erosion. Gully erosion is also significant in the Shiwalik tracts of Punjab, Haryana, Himachal Pradesh, Jammu and Kashmir, Uttarakhand, Uttar Pradesh and along the southern slopes of Himalayas, and the Western and Eastern Ghats.
Wind erosion is significant in the arid and semi-arid areas of Rajasthan, Haryana, Punjab, western Madhya Pradesh and Gujarat. Wind erodes soil along the coastal plains of Peninsular India. Thousands of hectares of fertile lands of Uttar Pradesh, Gujarat, Haryana, Punjab, and western Madhya Pradesh have been adversely affected by this process.
The tidal waters of the Arabian Sea and the Bay of Bengal cause considerable damage to the soils along the coastal areas. Severe erosion of beaches along the Kerala, Tamil Nadu, Andhra Pradesh, Orissa, and Gujarat coasts is the example of sea-wave erosion.
The largest area affected by soil erosion is in the state of Rajasthan, followed by Madhya Pradesh, Maharashtra, Uttar Pradesh, Gujarat, Andhra Pradesh and Karnataka. The worst affected areas of soil erosion include Chambal and Yamuna rivers, the southern slopes of Shiwaliks, Lesser and Greater Himalayas, the Western and Eastern Ghats, the Chotanagpur Plateau, and the arid and semi-arid areas of Rajasthan, Gujarat, Haryana, and Punjab.
Declining Soil Fertility: The main causes for decline in soil fertility are not utilizing soil for a lengthy period of time (centuries) and multiple cropping without fallowing the agricultural land. The farmers of Punjab, Haryana, and western Uttar Pradesh often complain about the decreasing fertility of their soils. The unscientific rotation of crops (wheat and rice) over several decades has depleted the soil fertility in the Great Plains of India substantially. The cultivation of leguminous crops after a soil exhaustive crop can improve the soil fertility affected regions.
Water-Logging: Water logging in an area occurs when the water table rises to the extent that soil pores in the root zone of a crop become saturated. This results in restriction of normal circulation of the air, decline in the level of oxygen, and an increase in the level of carbon dioxide. There are many ill-drained, low lying areas in India where the soil has been damaged by water-logging. Water logging has affected substantial tracts of land along the Indira Gandhi Canal (Rajasthan) and the canals of Punjab, Haryana, and Uttar Pradesh. Adequate development of drainage and lining of the canals to reduce water seepage can go a long way in the reclamation of water-logged areas.
Saline and Alkaline Soils: In areas with relatively less rainfall, soil suffers from salinity and alkalinity. This is due to the rate of evaporation being higher than the rate of precipitation. They also develop in the Khadar lands and the canal irrigated areas. Under such conditions, the ground water level rises and saline and alkaline efflorescence consisting of salts of sodium, calcium, and manganese appear on the surface as a layer of white salt through capillary action. It is estimates that about 80 lakh hectares (2.4% of the country's reporting area) has been adversely affected by saline and alkaline formations.
Salt Flats: The soils seriously damaged by the excess of calcium chlorides are found in the Rann of Kachchh. These soils are saline, marshy and infested with tall grasses, bushes and scrubs. They are almost useless from agricultural point of view. A sound strategy needs to be developed to bring the salt flats under agriculture or pastures. The Planning Commission, on the basis of data provided by the Ministry of Agriculture in 1985, mentions the types of degraded soils/land and their causes.
5.0 Soil Conservation in india
Soil is a very important resource and it is the basis of food supply of a nation. Though it is considered a renewable resource, soil loses its quality if abused or misused in the process of farming. Injudicious use of soil may lead to a variety of problems including soil erosion, declining fertility or contamination of soil. Soil erosion implies removal of top soil at a rate higher than the rate of accrual of new soil from the bedrock underneath. Excessive erosion reduces the depth of soil layer and may expose even the bed rock thus leaving land unsuitable for cultivation. Problem of soil erosion is most acute in hilly and dry regions. The most common causes of increasing erosion are the depletion of forests and faulty practices of land use such as cultivation on steep slopes and excessive grazing. Removal of plant cover exposes the soil to erosion by running water and wind, etc. A large area in central parts of the country has sandy soils that are highly prone to gully erosion and ravines and badlands are formed due to such erosion. The Chambal and Yamuna ravines are examples of such areas. In areas of large amount of rainfall soil is prone to sheet erosion where a part of the upper layer of soil is regularly removed by flowing water.
Increasing pressure of population leads to a higher intensity of land use in the form of multiple cropping and irrigated farming. Unless soil fertility is maintained, a high intensity of land use tends to reduce soil fertility. Soil fertility can be maintained by fallowing of land, rotation of crops and green manuring. However, the increasing demand for food and other crops due to a high pressure of population most of these natural methods of maintaining soil fertility become impractical. Therefore, application of manure and fertilisers is most common practice to maintain soil fertility. These days the concept of bio-fertilisers (growing of nitrogen fixing plants like various types of algae) and wormiculture (using earthworms, etc, to maintain soil fertility) are becoming popular.
Irrigation is necessary to support multiple cropping and cultivation of high yielding varieties. However, not all soils are suitable for intensive irrigation. In areas of poor soil drainage, soil may turn alkaline due to excessive irrigation. Increasing soil alkalinity is a major problem in many areas of India. Large tracts of land in Uttar Pradesh and the canal irrigated area of Rajasthan today suffer from this problem. Improving soil drainage and application of gypsum are recommended for reclaiming alkaline soils. Soil salinity is another problem resulting from excessive irrigation in many areas of semi arid climate. Excessive salinity may render soils impermeable and they might become unproductive. Soil contamination is also a problem in many areas today. It may be a result of excessive application of chemical fertilizers (a particular chemical compound accumulating in soil and ground water) or application of insecticides and weed killers. Contamination kills the micro fauna in the soil which contribute to maintaining soil fertility. Thus the natural process of soil maintenance is hampered.
Conservation of soil means maintaining the soils in good health so that crop production does not suffer. There are many methods of it suitable to different areas and for prevention of different problems. Soil erosion for example can be checked by maintaining a good plant cover so that soil is not exposed to agents of erosion. Other methods of soil conservation that can be adopted in different types of areas include contour ploughing, making of terraces on slopes, mulching (ploughing in of crops), construction of embankments and flood channels and scientific methods of cultivation keeping in view landform characteristics. Cultivation on the steep slopes and excessive grazing should also be avoided. Soil formation is a very slow process. Hence prevention of erosion is the best strategy.
Efforts should be made to maintain soil fertility naturally as far as possible and excessive use of chemical fertilizers, insecticides and weed killers must be avoided to prevent soil contamination. More scientific methods of application of chemical fertilizers can improve absorption of nutrients by plants more efficiently and this can help in checking over application. It will not only avoid soil contamination but also contamination of ground water into which the excess amount of chemicals tends to percolate and eutrophication of water bodies. Application of manure and bio-fertilizers can also help in this regard. Bio control of pests can also help in reducing the need of insecticides. Bio pesticides can also be used so that there is no accumulation of harmful chemicals in the soil. Biopesticides generally consist of micro organisms like bacterium, fungus, virus or protozoan as the active ingradient. Application of weed killers should be very judicious to avoid their over application and accumulation in soil.
Efforts should be made to reclaim soils that suffer from problems like alkalinity, salinity and water logging. This can add to the land resource available for agriculture and help in conserving forests also as most of the expansion in the cultivable area comes generally at the cost of area under forest. If used scientifically and judiciously the soils can sustain a high intensity of land use without losing their quality or capacity to sustain plant growth.
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