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Topic: Soil, Earth’s crust, Weathering, Pedogenic processes, , 1
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Soil, Concept, Word soil derived from LATIN word “ Solum” = Ground or floor, Land- 2D entity representing geographical area and landscape,, Soil- 3D body with length, breadth and depth and is hidden below the land, surface., They form a continuation over the land surface and differ in properties, from place to place. Its upper boundary is air or water and lower boundary is, the rock lithosphere., Approaches of Soil Study, Pedology- The study of genesis, survey, classification and geological, distribution of soils, Edaphology- Study of soil from the stand point of higher plants.
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Definitions, • Whitney (1892): Soil is a nutrient bin which supplies all the nutrients required for plant, growth, • Hilgard (1892): Soil is more or less a loose and friable material in which plants, by means, of their roots, find a foothold for nourishment as well as for other conditions of growth”, • Dokuchaiev (1900): Russian scientist - Father of soil science - Soil is a natural body, composed of mineral and organic constituents, having a definite genesis and a distinct, nature of its own., • Joffe (1936): “Soil is a natural body of mineral and organic constituents differentiated into, horizons - usually unconsolidated - of variable depth which differs among themselves as, well as from the underlying parent material in morphology, physical makeup, chemical, properties and composition and biological characteristics”.
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• Jenny (1941): Soil is a naturally occurring body that has been formed, , due to combined influence of climate and living organisms acting on, parent material as conditioned by relief over a period of time., , • Ruffin and Simonson (1968): Soil is a mixture of Earth’s uppermost, mantle of weathered rock and organic matter, , • Buckman and Brady (1969 ): Soil is a dynamic natural body on the, surface of the earth in which plants grow, composed of mineral and, , organic materials and living forms
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Pedon and Polypedon, Pedon- Smallest volume that can be called “a soil” is pedon. At the, same time, it must be large enough volume of soil to be observable, and, to exhibit a full set of horizons., ➢ Area- 1-10 m2 Shape- Roughly hexagonal, ➢It is 3D and Unit for soil sampling., ➢Set of pedons must fit within the range of one series and occur in a, continuous group to form a polypedon, Polypedon- Similar pedons bounded on all sides by pedons of unlike, characters. Minimum area more than 1 sq.km and an unspecified, maximum area., ➢Real soil bodies that we classify into series and higher categories
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Soil versus Regolith, Regolith- Loose unconsolidated inorganic material of weathered rock on the, earth’s surface., ➢It is the result of disintegration and decomposition of the exposed bed rock, ➢Parent material of soil. On this material the soil forming factors and processes, interplay to form true soil., ➢Weathered products of rocks and rock minerals are called as Parent materials, ➢Upper and biochemically weathered part of regolith- soil, Rock, , By weathering, , Regolith, (Unconsolidated, parent material), , By soil forming, factors and, processes, , True soil
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Composition of soil, ➢, ➢, ➢, ➢, , Mineral matter - 45%, Organic matter - 5%, Soil water, -25%, Soil air, - 25%, , Surface soil, , Subsurface soil, , Immediate uppermost loose, layer- Furrow slice, , Compact soil below furrow, slice, , 0-15 cm depth, , Cannot be cultivated by tillage, – hard pan formation, , Fertile, , Less fertile
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Soil Profile, Vertical section through a soil- showing all its horizons., Horizon- Layer approximately parallel to the surface of soil, Soil profile- up to a depth of 1.5-2 m in deep soils., In shallow soils vertical cut is made up to bedrock or up to water table in case, of waterlogged soils, Soil horizons are of two types, 1) Genetic horizons, 2) Diagnostic horizons, Genetic horizons, • Master horizons, • Transitional horizons, • Subordinate distinction within master horizons
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➢Top most Mineral horizon- A, ➢Horizon of eluviation- E, ➢Zone of accumulation- B, ➢Horizon represents the parent, material- C
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➢L horizon- Include both organic and mineral limnic materials that are, deposited in water by precipitation or through the action of algae and, diatoms. Found only in histosols, ➢M-layer- Root limiting subsoil layers. Geotextile liners, asphalt, concrete, rubber and plastic, ➢W –layer- It is water layer within or beneath the soil., Transitional horizons- The horizon which is dominated by properties of one, master horizon but having subordinate properties of another., Eg: AB, EB, BE, First symbol indicates horizon with the greater volume than another
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Subordinate distinctions within master horizons
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Earth’s Sphere, There are 3 spheres corresponding to three states of matter (solid,, liquid, and gas) which constitute the earth., ➢Solid sphere - Lithosphere, ➢Liquid sphere- Hydrosphere- the complete covering of water forming, seas and oceans, ➢Gaseous sphere- Atmosphere- the gaseous envelop over the Earth’s, surface
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ATMOSPHERE, • The envelop of air that covers both the lithosphere and hydrosphere., , • It contains water molecules and dust, which may act as nuclei for the condensation of, water vapour to form clouds or fog., • It composed of :, • Nitrogen, , : 78.084 % (Main component), , • Oxygen, , : 20.946%, , • Argon, , : 0.934%, , • Carbon dioxide : 0.04%, • In addition inert gases such as neon, helium, krypton, and xenon are present., • The water vapours present in the air vary in amounts at different places and times, • The air becomes less dense with height
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HYDROSPHERE, • Water covers almost three -fourth of the Earth’s surface., • Most of it lies within the ocean basins; it also appears on the surface of land, in the form of rivers, ponds, lakes, and as ground water, The quality of different water varies., • Sea water contains the highest amount of soluble salts ( EC 60,000 dS/m),, most of which is NaCl, • River water contains only a fraction of such salts. ( EC 591 dS/m, or even, less)
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LITHOSPHERE, • It is the solid surface, • Continents, ocean basins, plains, plateaus, mountains, valleys sand dunes,, lava flows and the interior of the earth which consists of rocks and, minerals., • It is covered by gaseous and watery envelope, , Atmosphere- 0.03% weight to the Earth, Hydrosphere- 6.91 %, Lithosphere- 93.06%
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INTERIOR OF THE EARTH, Thickness, , Density, , Crust, , 5-56 km, (5-11 km- Oceans, 35-56 km- continents), , 2.6-3 g cm-3, , Mantle, , 2900 km, , 3-4.5 g cm-3, , Core, , 3500 km, (Outer- 2250 km, Inner- 1300 km), , 9-12 g cm-3, , The density of the Earth - 5.5 g/cm3, Density of common rocks: 2.6 – 2.7 g/cm3, , ❖ Mantle- Rock composed of Si, O2, Al, Mg and Fe, 3, Density, of, heaviest, rock, :, 4, g/cm, Temp– 870 ° C (upper) and 4400 ° C (lower), ❖ Outer core- Melted Fe and Ni (2200 °C), ❖ Inner Core- Centre of Earth - Solid Fe and Ni (5000 °C)
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Composition of Earth’s Crust, • Hard and naturally- formed substance of the earth- Rock, • Out of 106 elements known, 8 are sufficiently abundant to constitute 98.6% of, earth’s crust upto 16km, The elements are geochemically distributed into 5 main groups on their bonding, characters:-➢Lithophiles - Which ionize readily or form stable oxyanions., ➢Chalcophiles - Which tend to form covalent bonds with sulphide., ➢Siderophiles - Which readily form metallic bonds., ➢Atmosphiles - Which tend to remain in atmospheric gases., ➢Biophiles - Which tend to be associated with living organisms.
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➢Dominant element in the Earth’s crust- Oxygen, ➢Second most abundant element- Si, ➢Dominant metallic element-- Al, ➢Dominant exchangeable cation- Ca, Name of the Element, , Percentage, , O2, , 46.6, , Si4+, , 27.72, , Al3+, , 8.13, , Fe2+, , 5.00, , Ca2+, , 3.63, , Na+, , 2.83, , K+, , 2.59, , Mg2+, , 2.09, , Others, , 1.41, , Non- metals-74.32%, , Metals—25.68%
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ROCKS AND MINERALS, Rocks, Rocks are a naturally occurring hard mass of mineral matter formed, after the solidification of molten magma comprising of two or more rock, forming minerals e.g. granite, basalt, and gneiss., But some may be monomineralic e.g. olivine, and dunite., ➢Petrology is the branch of science which study about the rocks., ➢Petrography -which gives information about description of rocks, ➢ Petrogenesis which deals with origin of the rocks, ➢Minerology- Study of minerals
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Rocks in the Earth Crust, Up to 5 km of the Earth’s crust, Igneous rocks-18%, • Granite -15%, • Basalt-3%, Sedimentary rocks- 74%, • Shale- 52%, • Sandstone- 15%, • Limestone & Dolomite- 7%, • Others- 8%, , Whole Earth’ crust, Igneous rock– 95 %, , Sedimentary rock- 5 %, • shale 4%,, , • sandstone- 0.75%, • limestone- 0.25%)
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Formation and Classification of Rocks, Igneous rocks:, • Non-laminar, massive structure, formed by cooling and crystalization of molten, materials (magma) on or beneath the earth surface., , • 95% of earth’s crust, , a. Based on origin, ➢Extrusive/ Volcanic- At the surface, fine size crystals,, Formed a glassy structure, Eg: Basalt, Rhyolite, Trachyte, ➢Intrusive/ Plutonic- Beneath the surface- Coarse grained, Eg: Gabbro. Granite, syenite diorite
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b. Based on chemical composition, ▪ 3 main classes- based on relative amount of acid and basic components- acid, neutral,, basic, ▪ Acidic component- silicic acid or silica, ▪ Basic components- soda, potash, Al, lime, magnesia, and iron oxides, ➢Acid/ Oversaturated- >60% silica – Eg: garanite, ➢Basic/ Under saturated- <50% silica – Eg: basalt
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Important Igneous Rocks, ▪ Basalt: Most abundant extrusive rock formed from molten magma. Fine grained, dark, coloured rocks, containing 50% feldspar and 50% ferromagnesian minerals (pyroxens and, olivine), basic in nature, ▪ Gabbro: Similar properties as basalt but coarse-grained., ▪ Granite: Coarse textured, light colour, acidic in nature, contain 60-70% feldspar (40-, , 45%, , orthoclase, 20-25% plagioclase), 20-30% quartz and 3-10% ferromagnesian minerals., ▪, , Rhyolite: Similar to granite but fine-grained., , ▪, , Pumice: Very light weight rock, specific gravity lower than water, thus it floats on water., Texturally, it is like a sponge.
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Sedimentary Rocks, Formed from sediments showing different stages of formation, ❖, , Weathering: Physical, chemical and biological weathering of primary rocks give, rise to quartz, secondary minerals and soluble substances (Ca, Mg, Fe, and salts.), , ❖, , Transportation: Transportation of weathered material by water, wind, glaciers and, runoff ., , ❖, , Deposition or sedimentation: Transported sediments settled to form graded, bedding. The coarse particles settle first followed by finer particles down the, stream., , ❖, , Diagenesis: Transformation of unconsolidated sediments to hard rock with, compaction and cementation processes.
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Important Sedimentary Rocks, ▪, , Shale: Fine grained detrital rock made up of clay and silt sized particles., , ▪, , Conglomerate: It is detrital rock made up of more or less rounded fragments. The, rock is termed as breccia, if the fragments are angular rather than rounded., , ▪, , Lime stone: It contains mainly calcite mineral, which is formed by precipitation., , ▪, , Sand stone: Mainly composed of quartz mineral. It is called arkose, if quartz and, feldspar are predominantly present. Its texture is intermediate between fine, grained shale and coarse grained conglomerate.
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Metamorphic Rocks, ▪ Developed from the transformation of existing rocks (igneous and sedimentary, rocks) by the process of metamorphism, which means “change in form”., ▪ The chemical or physical changes in their original form are brought by the heat, and pressure, ▪ Thermal metamorphism- Heat is the dominant factor, ▪ Also known as contact or additive metamorphism., ▪ Addition of magmatic material to the metamorphosed rock, , ▪ Dynamo thermal metamorphism- Pressure and Heat forms one of the most, powerful metamorphic force, ▪ Leading to more or less complete recrystallization of minerals with new structure, ▪ Associated with mountain building processes
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Granite, , Gneisses, , Thermal metamorphism, , Schists, , Dynamo thermal, metamorphism, , ▪ The structure and mineral composition of metamorphic rocks depend, upon the composition of the original rock and the kind of metamorphism., ▪ The banded or laminated character is the most peculiar feature of the, metamorphic rocks
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Pre-existing rocks and their equivalent metamorphic rocks, Pre- existing rock, Conglomerate/granite/syenite/gabbro, , Metamorphic rock, Gneiss, , Shale, , Slate, , Basalt, , Schist, , Sandstone, Limestone/Dolomite, Coal, , Iron ores, , Quartzite, Marble, Graphite, Haematite- schist
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Important Metamorphic Rocks, ▪, , Gneiss: Crystalline rock, bended appearance. Feldspar, quartz, mica, biotite and, muscovite are dominant minerals., , ▪, , Schist: Finely foliated or laminated rock. Mica and chlorite are dominant, , minerals., ▪, , Marble: Non-foliated, crystalline rock. Calcite and dolomite are dominant, , minerals., ▪, , Slate: Very fine foliated rock, splits into thin smooth sheets. Mica, quartz and, chlorite are dominant minerals.
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SOIL FORMING MINERALS, Minerals, A mineral is a naturally occurring homogeneous inorganic solid,, composed of atoms having orderly and regular arrangement with definite, chemical composition and characteristic geometric form., Formation of Mineral, • When molten magma solidifies, the different elements present therein freely arrange, themselves in accordance with the attractive forces and geometric form., • Geometrically it is possible to arrange only 4 oxygen atoms (with a radius of 1.32 Aº), around a central silicon cation (with a radius of 0.42 Aº) so that all are touching each other., • This is the arrangement of tetrahedron., • The silicate tetrahedron is the fundamental building block of all the silicate minerals of the, Earth's crust.
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▪ Charge carried by silicon ion is 4+ and oxygen is 2▪ In order to attain neutrality- one silicon (4+) ion would combine with two, oxygen ions (2 x 2-) to form SiO2, ▪ Geometrically stable SiO44-
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Classification of silicate minerals, Based on the tetrahedral linkage (sharing of oxygen) primary minerals are classified as, follows, 1. Nesosilicates (or) Orthosilicates (Island silicates) - No oxygen sharing and these are, made up of individual silicon tetrahedral (SiO4 4-), alternating with positively-charged metal, ions., Ex: Olivine (Fe Mg)2, SiO4, Fayalite Fe2SiO4, Forsterite Mg2 SiO4, , Zircon, Sphene, Topaz and Garnet
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Quartz (SiO2), • High degree of purity and strongly resistant to weathering, • Present in almost all soils, of which sand and coarse silt fractions contain, the largest, Pyroxenes and Amphiboles, Long chain of silica tetrahedra, also referred to as inosilicates, , Pyroxenes, Single chain, Found in basic rocks, Weather easily, Eg. Augite, , Amphiboles, Double chain, Found in acidic rocks, Weather slowly, Eg. Hornblende
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Mica, ▪ Potash mica: white, clear and transparent, known as muscovite mica, , ▪ Magnesium mica: Black , It is called biotite mica, ▪ White mica is more resistant than black
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Classification of Minerals, 1. Mode of origin as, Primary, , •, , Formed by crystallization of molten magma, , Silicate minerals, , Mineral, , •, , Inherited from igneous and metamorphic rocks, , Quartz, feldspar, pyroxenes,, amphiboles,, , •, , Formed at elevated temperature, , •, , Chemically remain unchanged., , •, , Percentage in soil depends on its sand and silt content, , ·, , Oxygen and silicon together or with one or, more cations are combined to form silicate, minerals which are more than 90% in the, earth crust., , hornblende, olivine, mica
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Secondary Formed by weathering of primary, , Silicates, , Non-silicates, , minerals, , minerals or inherited by soils from, , (clay, , Hematite (Fe2O3), , some sedimentary rocks, , Minerals), , Goethite (FeO(OH)n, , H2O), •, , Most common is clay minerals, , Kaolins,, , Gibbsite {Al(OH)3}, , •, , Other secondary minerals found in, , Smectites., , Calcite (CaCO3), , soils of arid and semi-arid (dry), , Vermiculite, Dolomite {Ca.Mg(CO3)2}, , regions are gypsum, calcite, apatite, , Mica, , Gypsum (CaSO4.2H2O), , etc., , Chlorite, , Apatite {Ca3(PO4)2}
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2. Quantity as, Accessory, , Occur only in small quantities in rocks but, , Minerals, , not essential (2-5%), , Essential mineral, , Non-silicate, , Zircon, , Zr(SiO4), , Form a group of heavy minerals due to, , Zeolite, , Ca, Na,and K silicates, , their high specific gravity, , Pyrite, , FeS2, , Magnetite, , Fe3O4, , Illemenite, , FeTiO3, , Barytes, , BaSO4, , Serpentine, , Mg6(Si4O10) (OH)8, , Forms major part of the rock (95-98%), Characteristic component of rock, , Calcite and Silicate minerals
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3. Specific gravity as, , Light minerals, , Having S.G below 2.85, , Quartz 2.6, Feldspar 2.65, Muscovite 2.5—2.75, , Heavy minerals, , Having S. G above 2.85, , Haematite 5.3, Pyrite 5.0, Limonite 3.8, Augite 3.1-3.6, Amphiboles 2.9—3.8, Olivine 3.5
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2. Striations - The parallel thread like lines or narrow bands running cross the, , surface of a mineral are called striations., • These are clearly observed on crystals of quartz, feldspars and pyrite., 3. Hardness - The resistance of a mineral to scratching is known as hardness., • The hardness is expressed in Mho's scale and identified by numerals (1-10)., • Talc is the softest and Diamond is the hardest mineral known
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4. Lusture- General appearance of a mineral in reflected light, • Characteristics of each mineral, 5. Transparency - It is the degree of penetration of light through a mineral, Eg: Transparent - Mica, Translucent - Quartz, , Opaque minerals - Pyrite and Magnetite, 6. Specific Gravity-It is the ratio between the weight of a mineral or a substance to the, weight of an equal volume of water., • Based on specific gravity minerals at substance divided into heavy minerals and light, minerals.
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7. Tenacity - The resistance that a mineral offers to breaking, crushing or bindings, known as tenacity., , 8. Cleavage - The tendency of a mineral to split in certain directions along smooth, plane surfaces is called cleavage., , Ex: Mica and Gypsum, 9. Fracture - Property of mineral to break along an irregular surface, , Ex: Glass and Quartz, 10. Pleochroism - Some minerals change colour when crystal is rotated on the, stage of the polarizing microscope., Ex: Albite, Hornblende and Tourmaline
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Some important points, ➢ Zoning is commonly exhibited by minerals which are grouped together, Isomorphous, Eg: Albite, Anorthite series of Plagioclase, ➢Orthoclase feldspars are liable to partial alteration, ➢ Magnetite shows a black appearance and Ilmenite shows silvery appearance in, reflected light, ➢Apatite, Muscovite and Augite liable to property of angle of extinction., ➢Siderite (FeCO3) mineral- mineral in waterlogged soils
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Weathering of Rocks and Minerals, Weathering, , refers, , to, , physical, , disintegration, , and, , chemical, , decomposition of rocks and minerals resulting in the formation of parent, material., It is basically a combination of transformation and synthesis or the, process of disintegration and decomposition of rocks and minerals which are, , brought by physical, chemical and biological weathering, leading to, formation of parent material.
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Classification of weathering process, Physical weathering :, A mechanical process causing disintegration of consolidated massive, rocks into smaller pieces under favourable climatic conditions through, various agents viz. temperature, water, ice and wind
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a) Temperature, • A differential expansion and contraction of minerals occurs owing to diurnal temperature changes resulting in, peeling off the surface layers from the rocks (breakdown into small fragments)., • This phenomenon is called as exfoliation or onion- type weathering., • Eg: Basalt and granite, • Cold temperature causes freezing of entrapped water inside the rock which expands 9% in volume and exerts a, pressure of about 1465 tonnes/m2 (t m-2) resulting in the break-down of rocks., , b)Water, •, , Most pronounced and widespread weathering agent., , •, , Action of flowing water - collision of rocks-- formation of smaller fragments -transported and deposited at, the far-off places., , •, , Sediment-loaded water has tremendous capacity to cut the rocks and hard surfaces-- gorges, ravines and, valleys are formed.
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c)Ice, •, , Moving ice or glaciers cause great deal of cutting and crushing of the bedrocks., , •, , On moving, glaciers exert a tremendous pressure, , •, , The loose material moves forward and gets deposited- This deposit is called Moraine., , •, , Eg: The huge boulders seen in Kangra valley of Himachal Pradesh, , d) Wind, • An important agent of transportation of suspended particles, • Also exerts an abrasion effect - more pronounced in the aridic climates., • Poorly grained or single – grained deposits are more prone to the wind erosion., • Eg: The rounded rock (Mushroom rock) remnants in the Aravalis, Prominent in Thar desert of Rajasthan.
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Chemical Weathering:, • Decomposition process - takes place primarily at the junction of lithosphere and atmosphere called, weathering front., • It leads to alteration or disappearance of some minerals and formation of new minerals., • This process is generally dominant in tropical than in arid climate and governed by various agents., • The rate of chemical weathering increases with increasing amounts of dissolved CO2 and other, minerals in water., • The presence of organic and inorganic acids accelerates the chemical weathering., , • The chemical weathering has great role in conversion of primary minerals (feldspars, mica,, amphiboles etc.) into secondary minerals (kaolinite, montmorillonite, vermiculite etc.)., • Most important process in soil formation
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a) Solution, • Water is a universal solvent and its solubility action is enhanced with dissolved, CO2, organic and inorganic acids or salts in it., • Decomposition of rocks depends on composition of rocks and solubility action of, water., • Eg: halite (NaCl) is readily soluble, quartz is sparingly soluble, , • H2O+ CO2, , H2CO3
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c) Hydrolysis, •, , Hydrolysis is one of the most important processes of chemical weathering., , •, , Dissociation of water (H2O) into hydrogen (H+) and hydroxyl (OH-) ions., , •, , It is a type of double decomposition process, in which CO2, minerals and organic acids-rich water get, , easily dissociated into H+ and OH- ions which chemically combine with a mineral and form a new, mineral., •, , Hydrolysis reactions may be considered as the fore- runner in clay formation (secondary clay minerals)., , H2O, KAlSi3O8 + H2O, (orthoclase), , H+ + OHHAlSi3O8 +KOH, (Clay minerals)
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d) Oxidation, •, , Oxidation is combination of oxygen dissolved in water or from atmospheric air, with exposed rocks or minerals., , •, , It is an important chemical reaction occurring in the well-aerated rock and soil, , materials where oxygen supply is high and biological demand is low., •, , Rocks containing pyroxenes, hornblende, biotite, glauconite and chlorite etc. are, , susceptible to oxidation- Contain Mn2+ and S2•, , 4FeO +O2, , 2Fe2O3, , •, , 4Fe3O4 +O2, , 6Fe2O3, , (Magnetite), , (Haematite)
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e) Reduction, •, , The process of removal or loss of oxygen is called reduction., , •, , Occurs where a mineral is water-saturated, oxygen supply is very low and biological demand, of oxygen (BOD) is very high,, , •, , Conversion of the higher valent metals to the low valent states (e.g. Fe3+ into Fe2+)., , •, , Lepidocrocite is also formed in this condition which imparts orange and yellow mottles to soil, matrix under reduced conditions., •, , 2Fe2O3, , 4FeO +O2, , •, , 6Fe2O3, , 4Fe3O4 +O2
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f) Carbonation, • Carbonation is the combination of carbon dioxide with any base., • When water reacts with CO2 it gives carbonic acid (H2CO3), which is a very, important agent of chemical weathering of rocks and minerals., • The solubility of calcium bicarbonate (CaHCO3) is considerably higher than that, , of calcite (CaCO3)., • H2O+ CO2, , H2CO3, , • CaCO3 + H2CO3, , CaHCO3, , (insoluble), , (soluble)
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Important Points…., ➢Most important chemical weathering process- Hydrolysis, ➢Most important chemical weathering process in primary minerals- Hydrolysis, ➢Results in complete disintegration and drastic modification of primary mineralsHydrolysis, ➢Most important chemical weathering process in secondary minerals- Hydration, ➢Double decomposition process- Hydrolysis, ➢Forerunner of clay formation- Hydrolysis, ➢Vermiculite can be formed from muscovite by Hydrolysis, ➢Serpentine formed from olivine by Hydration, ➢Haematite from magnetite by Oxidation, ➢Bog iron from Haematite by Hydration
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Biological Weathering, • Change brought by living agents - controlled by prevailing environment -, , responsible for both physical and chemical changes., • The mosses and lichens growing on rocks secrete chemical exudates which act, chemically on the minerals present in the rocks and tend to form new minerals., • Burrowing animals, movement of animals and human activities facilitate the, physical weathering.
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Weathering index, - Jackson (1964)
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Stages of weathering, Name of stage, , Stage of weathering, , Initial, , Un weathered parent material, , Juvenile, , Weathering just started but most of the original, material can be seen, , Virile, , Less resistant minerals decompose easily and, increase clay content, , Senile, , Only resistant minerals can be seen like quartz, , Final, , Formation of soil over
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SOIL FORMING FACTORS, • Dokuchaev (1889) established that the soils develop as a result of the action of soil, forming factors, S= f (p, cl, o), • Jenny (1941) – added two factors- relief and time, S= f (cl, b, r, p, t), , S= f (cl, b, r, p, t)- Jenny (1941), cl- climate, Active, b- biosphere, , Joffe, (1949), Passive, , r- Relief, p- Parent material, t- Time
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Climate, ➢Most influential factor – Precipitation and Temperature, ➢Rainfall- more significant climatic element, ➢Arid climate- Saline soils, , ➢Cool humid climate- Podzols, ➢Warm humid climate- Laterites, , ➢Temperature- Second most important, ➢Van’t Hoff Law- With every 10 0C rise in temperature, speed of chemical reaction, , increases by a factor of two or three
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Biosphere, ➢Macro-organisms such as rodents, moles, snails, earthworms, termites, milliped, centipedes etc.- burrowing habit, cause mixing of soil material, ➢Retard the differentiation of soil horizons and as a consequence retard the process of, soil development, ➢ Microorganisms such as bacteria, fungi actinomycetes, protozoa and nematodes-, , decomposition of organic matter, ➢Rapid decomposition of mineral and organic matter leads to formation of soil
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Relief or Topography, ➢Configuration of land surface describe in terms of elevation or slope, ➢Gently-sloping flat land is ideal for soil development, ➢Soil Catena-Milne (1935), ➢A sequence of soil developed from similar parent material under similar climatic, conditions but under varying conditions of relief.
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Parent Material, ➢Jenny (1941) defined parent material as “the initial stage of soil system, ➢Loose unconsolidated mass of mineral matter formed upon the weathering, of rocks which serves as the raw material for soil formation., , ➢The initial stage of soil formation and soil properties are governed by the, nature of parent material but with the time the influence of parent material, , on soil properties gradually diminishes., ➢Residual- (formed in place/ insitu) Soils are developed at a place from the, underlying rocks, , ➢Transported-
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Time, ➢The period of time devoted by the nature from the stage of parent material to the stage, of soil formation is considered as “pedologic time", , ➢Warm humid climate, flat to gently sloping topography, sandy parent materials are, favourable for soil formation, ➢Cold and arid climate, clayey parent material, steep slope, flood plains and activities, of burrowing animals retard the pace of soil profile development
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Soil Forming Processes, The basic processes (According to Simonson), 1. Addition or gain of water, mineral and organic matter in the soil, , 2. Losses of the above materials from the soil, 3. Transformation of mineral and organic materials with in the soil, , 4. Transfer or translocation of energy and matter (mineral or organic)
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Fundamental Pedogenic Process, 1. Humification- It is the process of transformation of raw organic matter into humus, • Raw organic materials - simple organic acids- Bacterial polymerizationcolloidal substance resistant to microbial attack is called humus, , dark brown, , 2. Eluviation (Emigration) - Process of removal (wash out) of soil constituents, This process occurs in E-borizon or A2 horizon of soil profile., Order of mobility of inorganic soil constituents, Cl>SO4>Ca> Na >Mg>K>SiO2 > Fe2O3>AI2O3, , expressed, , relative, , to, , 3. Illuviation (Immigration)- Process of deposition of simpler soil constituents removed, from upper layer to the lower layer, • This process occurs in B-horizon of soil profile
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Zonal Soil Forming Processes, The soil forming processes that are occurring under the prevailing conditions of, climate and biosphere, , Intrazonal Soil Forming Process:, These pedogenic processes are more influenced by certain local conditions such, , as relief or parent material than climate and vegetation., Ex: Hydromorphic, halomorphic and Calcimorphic soils
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Zonal Soil Forming Process, a) Calcification, ▪ Process of precipitation and accumulation of calcium carbonate (CaCO3) in, , some part of soil profile is called calcification, ▪ occurs in arid and semi arid climates, , b) Decalcification, ▪ Process of removal of caco3, or ca ions from the soil by leaching, , ▪ Process occurs in the humid climates
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C) Podzolization, ➢Process of accumulation of silica and removal sesquioxides (Fe and Al oxides), ➢“Acid hydrolysis” - pH. of soil remains below 5.0 due to the leaching of bases, , ➢Climate cold-humid, ➢Vegetation - coniferous (acidic nature and narrow leaf), , ➢Parent material- sandy (siliceous), ➢Dominant organism - fungi
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d) Laterization, ➢Process of accumulation of sesquioxides and removal of silica., ➢Alkali hydrolysis- pH remains alkaline to neutral., ➢Climate- Warm-humid, ➢Vegetation- Broad leaf tropical vegetation (basic nature), ➢Parent material- Basic parent materials that contain high Fe, (Ferromagnesian minerals), ➢Dominant organism- Bacteria
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Intrazonal Soil Forming Process, a) Gleization, • Process results in the development of a gley horizon (g) in some part of profile due to poor, drainage condition, impervious soil parent material, lack of aeration etc., , • Hydromorphic soils will be developed due to Gleization process., , b) Salinization, • The process of accumulation of salts such as SO42- and Cl- of Ca, and Mg in soil in the form, of a salic horizon (z) leading to formation of saline soil, • In arid and semi arid climate, • White alkali soils/ Solonchalks
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c) Alkalization, • Process of accumulation of sodium ions on exchange complex of the clay- alkali soils, • Black alkali soils- Sodic/Solonetz, • Contains mostly carbonate and bicarbonate of Na, , Dealkalization/ Solodization- Removal of Na from exchange sites, d) Pedoturbation, Process of mixing of soil materials, • Faunal Pedoturbation - Mixing of soil by animals, • Floral Pedoturbation - Mixing of soil by plants, • Argillo Pedoturbation - Mixing of soil by churning process caused by swell shrinking of clays
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• Clay migration" or Lessivage - Removal of clay, particularly of fine clay in, , suspension from the upper part of soil profile and its accumulation in lower part., • Braunification or Rubification or Ferruginisation - Release of Fe from primary, , minerals and their dispersal as coatings on soil particles or as complexes with, organic matter/clay or as discrete aggregates to impart a brown to red colour to the, soil., • Regur Formation - Formation of intensity dark colour complex of smectite clay, and humus. Dominant process in black cotton soils
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Lets Discuss Now.., , 89
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Soil Science, The science dealing with soil as a natural resource on the surface, of the earth, including Pedology (soil genesis, classification and, mapping), physical, chemical, biological and fertility properties of soil, and these properties in relation to their management for crop, production.”, Soil is at the interface between the atmosphere and lithosphere. Its upper, limit is air or water.
