Soil Science Session 1 PDF

WEATHERING AND SOIL FORMATION Difference between SEDIMENTATION and LITHIFICATION: A. ROCKS AND PETROLOGY Petrology Sedimentation – collective term fo...

WEATHERING AND SOIL FORMATION Difference between SEDIMENTATION and LITHIFICATION: A. ROCKS AND PETROLOGY Petrology Sedimentation – collective term for step 1 to Petros = rocks step 3 → weathering, transport, and Logia = study of deposition Study of rocks concerned with Lithification – refers to step 4 → compaction composition, structure, and origin and cementation → from unconsolidated Rocks material (sediments) to consolidated (rock) Aggregates of different kinds of minerals 3. Metamorphic rocks in varying proportions E.g. granite contains minerals such as Metamorphism – change in structure or biotite, quartz, and feldspar composition due to heat and pressure Form from pre-existing rocks such as B. TYPES OF ROCKS igneous and sedimentary rocks 1. Igneous rocks subjected to heat and pressure From Latin word ‘Ignis’ meaning Fire Metamorphic Rock Pre-existing rock Forms from solidification of hot molten Equivalents material such as magma and lava Sandstone Quartzite Most abundant rock in the Earth’s crust – Limestone Marble 95% Conglomerate Meta-conglomerate Intrusive Igneous Extrusive Igneous Shale Slate (Plutonic) (Volcanic) Basalt Schist From lava upon rapid Granite Gneiss From trapped magma cooling Slow cooling Fast cooling Coarse-textured due to Fine-textured due to C. ROCK CYCLE crystal growth lack of crystal growth Granite, gabbro, Basalt, rhyolite, Continuous transformation of different types diorite, pegmatite andesite of rocks through geologic time Texture of Igneous Rocks Coarse-textured → Intrusive Phaneritic Igneous Aphanitic Fine-textured → Extrusive Igneous Larger crystals (PHENOCRYST) Porphyritic surrounded by matrix of smaller crystals (groundmass) 2. Sedimentary rocks Forms from the compaction and D. ABUNDANT ELEMENTS IN THE EARTH’S cementation of sediments of pre-existing CRUST rocks such as igneous and metamorphic 1. Oxygen – 46.6% rock subjected to weathering 2. Silicon – 27.72% 1. e.g. Sandstone 3. Aluminum – 8.13% 4. Iron – 5.00% May also form from parts of living organisms 5. Calcium – 3.63% 1. e.g. Bituminous coal (from plant) 6. Sodium – 2.83% 7. Potassium – 2.59% Major processes of sedimentary rock 8. Magnesium – 2.09% formation 9. Others elements – 1.41% 1. Mechanical and chemical weathering of parent material E. MINERALS AND MINERALOGY 2. Transport of weathering products Minerals through water, gravity, wind or ice Naturally occurring inorganic substance 3. Deposition of sediments that has definite internal arrangement 4. Compaction and cementation and definite chemical composition and physical properties Mineralogy Study of minerals concerned with structure and properties F. CLASSIFICATION OF MINERALS o e.g. Hydrolysis of Kaolinite → Silt clay 1. Primary minerals Form from crystallization of igneous d) Hydration rocks o Water is absorbed in the mineral Source of sand and silt fractions structure e.g. Olivine, Pyroxene, Amphibole, o Does not destroy chemical Plagioclase, Mica structure o Black mica = Biotite e) Carbonation o White mica = Muscovite o Rocks or mineral with carbonic 2. Secondary minerals acid Form from weathering of pre-existing 3. Biological weathering minerals a) Root wedging – entry of plant roots in Source of clay fraction small cracks which causes further cracks e.g. Pyrite (Fool’s gold), Halite (salt or as it grows NaCl), Kaolinite (clay mineral), Hematite b) Animal activity (oxidized iron) o Burrowing and excavation of animal G. BOWEN’S REACTION SERIES o e.g. Piddocks 1. Discontinuous series I. SOIL left branch where minerals such as Olivine, Pyroxene, Amphibole, and Definition of Soil (Soil Survey Staff, 1999) Biotite can be found natural body comprised of solids High magma temperature (minerals and organic matter), liquid, and High in Iron and Magnesium but low in gases that occurs on the land surface, Silica occupies space, and is characterized by one or both of the followings: horizons or 2. Continuous series layers, that are distinguishable from the Right branch → from Calcium rich to initial material as a result of additions, Sodium rich losses, transfers, and transformations of form as temperature decreases in a more energy and matter or the ability to support gradual and continuous manner rooted plants in a natural environment 3. Residual phase Well-known Soil Scientists discontinuous and continuous series join Vasily Dokuchaev – Father of Soil Low in Fe, Mg, and Ca but high in Silica Science H. WEATHERING o Born in Russia o Considered soil as a living system 1. Physical weathering a) Exfoliation – observable cracks caused Hans Jenny – 5 Factors of Soil Formation by pressure release during uplift and o Born in Switzerland erosion o Most acknowledged model b) Freeze-thaw – water enters cracks and (CLORPT) expands rock upon freezing c) Thermal expansion – cracking of rocks due to repeated expansion (high J. 5 FACTORS OF SOIL FORMATION temperature) and contraction (low 1. Climate temperature) a) Temperature d) Abrasion – collision of rocks resulting to o Rate of biochemical reaction is smooth surface faster with high temperature, thus 2. Chemical weathering faster weathering a) Oxidation b) Precipitation / Rainfall o Combination of oxygen to o Higher rate of precipitation means minerals higher rate of weathering and o Loss of electrons leaching o Oxidation of magnetite to o Leaching – soluble substances hematite are translocated through water b) Reduction NOTE: Tropical soils are usually older o Removal of oxygen to minerals due to higher temperature and o Gain of electrons precipitation as compared c) Hydrolysis – attack of water to minerals temperate soils which are usually which causes: young soils o Change in mineral composition o Change in mineral structure o Decomposition  2. Living Organism K. NAMING SOIL HORIZONS a) Animals o Bioturbation causes soil mixing 1. O horizon – part of Topsoil ▪ e.g. Termite mounds Layer of organic matter at various stages b) Microorganisms of decomposition o Fungi and bacteria help in Oi (Fibric) – undecomposed or slightly decomposition of organic matter decomposed c) Plants Oe (Hemic) – moderately decomposed o Source of organic matter in the Oa (Sapric) – highly decomposed soil 2. A horizon – part of Topsoil Grassland Soil Forest Soil Mineral horizon Organic matter coats the minerals (sand, Thick surface horizon Thin surface horizon (A silt, and clay) which causes darkening of (A horizon) horizon) soil Darker A horizon due to Formation of thin O organic matter horizon 3. E horizon Zone of ELUVIATION → EXIT 3. Relief / Topography Zone of leaching → Clay, OM, and a) 5 Hillslope position sesquioxides (Fe/Al oxides) are leached Light colored Fast development of soil due 1. Summit to high leaching and relatively 4. B horizon - Subsoil 2. Shoulder less erosion as compared to Zone of ILLUVIATION → INTO backslope Zone of accumulation → accumulation of Slow development of soil due leached Clay, OM, and sesquioxides 3. Backslope to less leaching and faster (Fe/Al oxides) from overlying horizons runoff causing soil erosion NOTE: O, A, E, and B horizons are Slow development of soil due considered Solum or True soil → 4. Footslope to accumulation of sediments “Zone of pedogenic activity” 5. Toeslope from upslope (humification and weathering are Prone to flooding dominant) 5. C horizon 4. Parent material Outside the zone of pedogenesis a) Residual – from the bedrock Partially weathered parent material b) Transported – water, wind, gravity, or ice Weathered or soft bedrock o Water – alluvium Regolith o Wind – aeolian o Gravity – colluvium 6. R horizon o Ice – glacial drift Unweathered parent material 5. Time Hard bedrock (cemented/consolidated) Developed horizons Iron and clay accumulation Increase acidity L. SOIL HORIZONATION Leaching 1. Horizonation Time zero – initial state of the soil system Includes processes and conditions by NOTE: Age of soil is not considered in which initial materials are differentiated number of years but in the into soil profiles with many horizons number of soil horizons that e.g. Illuviation, Eluviation, Podzolization, developed Littering A A E 2. Haploidization Includes processes and conditions by Young which horizonation is inhibited or B C Old decelerated or by which horizons are C mixed or disturbed e.g. Erosion and Pedoturbation M. GENERAL PROCESSES OF SOIL organic matter, resulting in concentration FORMATION of silica in the layer eluviated e) Laterization / Desilication – chemical Simonson’s model → Soil = f (a, r, t1, t2) migration of silica out of the soil solum a = addition and thus the concentration of r = removal/losses sesquioxides in the solum t1 = translocation f) Braunification, Rubification, t2 = transformation Ferrugination – release of iron from NOTE: These general processes are primary minerals and the dispersion of regulated by 5 factors of soil particles of iron oxide in increasing formation (CLORPT) amounts; their progressive oxidation or 1. Addition hydration, giving the soil mass brownish, a) Enrichment – general term for any reddish brown, and red colors, material added to soil body respectively b) Melanization – darkening of light- g) Gleization – reduction of iron under colored mineral by admixture of organic anaerobic “waterlogged” soil conditions, matter with the production of bluish to greenish c) Cumulization – aeolian, hydrologic, and gray matrix colors, with or without man-made additions of mineral particles yellowish brown, brown, and black to the surface of a soil solum mottles, and ferric and manganiferous d) Littering – accumulation on the mineral concretions soil surface of organic litter and associate h) Lessivage – washing in suspension of humus to a depth of less than 30cm fine clay down cracks and other voids in a soil body 2. Removal i) Illuviation – movement of material into a a) Erosion – removal of material from the portion of soil profile as in an argillic or surface layer of a soil spodic horizon b) Leaching – general term for washing out j) Calcification – processes including or eluviating soluble materials from the accumulation of calcium carbonate solum L. PEDOTURBATION / BIOPEDTURBATION 3. Transformation a) Decomposition – breakdown of mineral 1. Faunalturbation – soil mixing by animals and organic materials 2. Floraltubation – soil mixing by plants b) Synthesis – formation of new particles of 3. Argilliturbation – soil mixing by action of mineral and organic species clay (shrinking and swelling) c) Mineralization – release of minerals 4. Cryoturbation – soil mixing by freezing and components (inorganic) of organic matter thawing of ground ice through decomposition d) Humification – transformation of raw ADDITIONAL TERMS: organic materials into humus e) Ripening – chemical, biological, and 1. Concretions – redoximorphic feature, physical changes in organic soil after air compact (cemented) mass of mineral matter penetrates previously waterlogged soil 2. Hectare furrow slice – 2,000,000 kg f) Loosening – increase in volume of voids 3. Pedon – smallest volume of soil that should by activity of plants, animals, and be recognized as a soil individual humans and by freeze-thaw or other 4. Polypedon – composed of several physical processes and by removal of homogeneous pedons material by leaching 5. Saprolite – chemically weathered rock that g) Hardening – decrease in volume of has remained on original site (in situ) and has voids by collapse and compaction and by preserved original rock structure filling of some voids with fine earth, 6. Soil horizon – layer parallel to soil surface carbonates, silica, and other materials whose physical, chemical, and biological characteristics differ from layers above and 4. Translocation beneath. a) Salinization – accumulation of soluble 7. Soil Profile – vertical exposure that includes salts such as sulfates and chlorides of all material that has been altered by chemical, calcium, magnesium, sodium, and physical, and biological reactions; composed of potassium in salty (salic) horizons soil horizons b) Alkalization / Solonization – 8. Transitional horizon – horizon contains accumulation of sodium ions on the characteristics of two horizons but one is exchange sites in a soil dominant over the other (e.g. AB horizon) → c) Dealkalization / Solodization – leaching characteristics of A horizon is more dominant of sodium ions and salts from nitric than B horizon horizons d) Podzolization / Silication – chemical migration of aluminum and iron and/or