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Soils Notes

by: Cj Sivulka
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Notes from soil lecture
Intro to Physical Geography
Dr Stereletskiy
Class Notes




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This 6 page Class Notes was uploaded by Cj Sivulka on Wednesday May 4, 2016. The Class Notes belongs to Geog 1002 at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months taught by Dr Stereletskiy in Spring 2016. Since its upload, it has received 14 views. For similar materials see Intro to Physical Geography in Geography at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months.

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Date Created: 05/04/16
 Soil – relatively thin surface layer of mineral matter that normally contains a considerable amount of organic material and is capable of supporting living plants; o About 6 inches deep o combination of mineral and organic matter, water and air, living organisms, liquid solutions, etc o 25% air, 25% water, 5% organic matter, 45% mineral matter / parent matter (rock fragments); all of which support plant growth  regolith – broken and partly decomposed rock particles; covers bedrock; kind of like a blanked over the unfragmented rock below the soil  Humus – dark colored semi soluble organic substance formed from decomposition of organic matter; “black gold;” loosens the structure and density of soil o Decomposition is the chemical or physical breakdown of a mass of matter into smaller parts or chemical elements  5 Factors of Soil formation o Parent Material – the source of rock fragments that make up the soil  Composition has a direct impact on soil chemistry and fertility  Ones rich in nutrients (e.g., limestone and basaltic lava), are  easily dissolved in water and made available to plants.  If low in soluble nutrients (Sandstone), water moving through the  soil removes them and substitutes with hydrogen making the soil  acidic and unsuitable for agriculture.  o Influence on soil properties tends to decrease with time as it is altered and climate becomes more important  o Climate  Temperature and moisture are the strongest influencers to soil formation (they influence physical and chemical reactions on the parent material)  Climate also determines the vegetation cover which in turn  influences soil development by producing organic matter.  Precipitation also affects movement of matter through soil.  As time passes, climate tends to be a prime influence on soil properties  while the influence of parent material is less.   Soils tend to show a strong geographical correlation with climate,  especially at the global scale. o Topography  Slope and drainage influence it  When soil develops, its vertical extent is continuous and slow changing  Topography determines runoff of water, and its orientation affects  microclimate which in turn affects vegetation.  For soil to form, the parent material needs to lie relatively undisturbed so  soil horizon processes can proceed.  Water moving across the surface strips parent material away impeding soil development.  Steep slopes have poorly developed soils •Flatter terrain accumulates soil  faster  Soil is thinner on slopes because of erosion  Steep slopes don’t have any soil development   Residual soil is developed on bedrock o Vegetation / Biological factor  Influences it through litterfall and process of decomposition because organisms add organic matter and nutrients to the soil which influences soil structure and fertility  Surface vegetation also protects the upper layers of soil from erosion  Animals live in the soil and can tunnel through it Vegetation roots provide aeration and drainage roots  Nutrient Cycling  Biotic elements of the environment need life­sustaining nutrients  that find their origin in the soil.   Upon their death, organisms return these nutrients to the soil to be  taken up again by other plants and animals.  Hence there is a constant cycling of nutrients between organisms  and soils.   Without it, soluble nutrients would be removed from the soil by  percolated water, decreasing the soil's ability to support life. o Time – slow process  Influences the temporal consequences of all of the factors described  previously  Soils get better developed (Thicker, with greater differences between  layers) with more time  Climate interacts with time during the soil development process.  Soil development proceeds much more rapidly in warm and wet climates  thus reaching a mature status sooner.  In cold climates, weathering is impeded and soil development takes much  longer.  Horizons – soil layers  Soil profile – all the soil horizons taken together; from surface to bed rock  Horizon development process; basically what goes in and out of the soil and how stuff moves around in the soil o Additions (for soil enrichment): water, oxygen, carbon, nitrogen, chlorine, sulfur, organic matter, sediments, energy from the sun o Translocation: clay and organic matter carried by water, nutrients circulated by plants, soluble salts carried in water, soil carried by animals, chemicals, o Transformation: organic matter converted to humus, particles made smaller by weathering, structure and concentration formation, minerals transformed by weathering, clay and organic matter reactions o Loss / Removal: water and minerals in solution or suspension; chemicals, particulates, organic matter  Soil movements o Eluviation – downward transport of fine soil particles, removing them from the upper soil horizon o Illuviation – accumulation in a lower soil horizon of materials eluviated from higher horizons  Soil Horizons o O horizon – loose and partly decayed organic matter o A – mineral matter mixed with some humus; dark colored horizon of mixed mineral and organic matter and with much biological activity o E – zone of eluvation and leeching; a alight colored horizon marked by removal of clay particles, organic matter, and/or oxides of iron and aluminum o B – accumulation of clay, iron and aluminum, from above; zone of illuviation o C – partially weathered parent material o R – unweathered parent material; consolidated bedrock  Soil in Boreal forests – (spodosols); pine trees have low nutrient demands so the litter is poor; little cycling of the nutrients occurs; precipitation also flushes some organic material from the soil  Soil in the warm and wet tropics – (oxisols); Bacterial activity proceeds at a  rapid rate, thoroughly decomposing leaf litter; Available nutrients are rapidly taken back  up by the trees; High annual precipitation flushes some organic material from the soil;  Create soils lacking much organic matter in their upper horizons.  Soils in grasslands – (mollisols); some of the richest in the world; lots of rich humus; fast accumulation of nutrients; low leaching  Soil Properties o Color - A product of soil forming processes; usually red, gray or white, or black or brown; colors give strong hints about soil fertility o Texture – refers to the relative proportion of sand, silt, and clay size particles in a sample of soil; sand, slit, clay refer to particle size; you use a soil texture triangle to classify the texture class o Structure – refers to the way in which soil grains are grouped together into larger masses (peds – an individual natural soil aggregate); soil structure has a major influence on water and air movement  Granular structure – where the structural units are approximately spherical and are bounded by curved or irregular faces (look like cookie crumbs!); allows water and air to penetrate the soil  Blocky structure - the structural units are blocklike; the strongest blocky structure is formed as a result of swelling and shrinking of the clay materials which produce cracks  Platy structure – looks like stacks of dinner plates overlaying one another; platy structure tends to impede the downward movement of water and plant roots through soil o Soil water  Infiltration capacity is the maximum rate at which water (falling rain or melting snow can be taken in (absorbed) by soil through the surface)  Infiltration capacity – amount (depth) / time o F = d/t  Different values of F for different soil textures o EG: coarser soils have higher infiltration capacity  Field / storage capacity – maximum capacity of soil to hold water against the pull of gravity  Sand is 7%; peat is greater than 170%  Types of soil water  Hydroscopic water – water that is bound to soil particles due to molecular forces; can’t be evaporated, used by plants, or removed by any other natural process  Capillary water – the part of soil water which is held as a continuous layer around particles; most of it is available to plant roots  Gravity water – subsurface water that responds to gravitational force, percolating it through the soil o Chemistry –  some elements are required for plant growth  Calcium (Ca++)  Magnesium (Mg++)  Potassium (K+)  Sodium (Na+)  Colloids  Plant nutrients (bases) are attracted and held by very small organic  and mineral particles (colloids).   Colloids generally have a net negative charge as a result of their  physical and chemical composition.   One of the most important properties of colloids is their ability to  attract, hold, and release ions.  Ion Exchange­  the exchange of an ion in the soil for another on the  surface of a colloid.   The capacity of a soil to retain and exchange ions, is called its  exchange capacity.  o Exchange capacity ­ measure of the chemical reactivity of  the soil, varies inversely with particle size. Fine soils  accumulate and retain many times more ions than do coarse soils. The exchange capacity of the soil's colloidal particles is of tremendous importance. Nutrients that would  otherwise be washed away are held in reserve and become  available to the plant.  Cations differ in their ability to replace one another; if present in equal  amounts, H+ replaces Ca++ replaces Mg++ replaces K+ replaces Na++. If one ion is added in large amounts it may replace another by sheer force of  number. This is largely what occurs with the addition of fertilizer. The  release of hydrogen ions in soils tends to promote the exchange of ions,  making them available to plants.   Ph - H+ concentration in the soil is measured in terms of the pH scale.  Soil pH ranges from 3 to 10. Pure water has a pH of 7 which is considered  neutral, pH values greater than seven are considered basic or alkaline,  below seven acidic. Most good agricultural soils have a pH between 5 and  7.  Pdeogenic regimes –  Laterization Eluviation and leaching of A horizon in wet warm  climates (red soils, Fe, Al)  Podzolization Eluviation and leaching of A horizon in cold  temperate climates (ash like A, yellow B)   Gleization Reduction of Fe+++ to Fe++ in anaerobic environment   Calcification Calcic hardpans (prairies/steeps) in dry conditions   Salinization Accumulation of chlorides, sulfates in desert climates   Naming and Labeling of Soils o Soil taxonomy – generic; soil is organized based on observable soil  characteristics; focus on the existing properties of the soil rather than on the  environment, process of development, or other properties   Classifications  o Alfisols  Al stands for aluminum and F stands for iron; lots of these 2 elements in  the soils; clay accumulation with high bases; most wide ranging of mature  soils  o Andisols  Andesite, rock formed from a type of Magmum in the Andes Mountans  volcanoes; lots of ash o Aridisols  Dry soils; 1/8 of the earth’s surface; requires irrigatoin o Entisols   Very little profile development; sandy / droughty conditions; 12% in Us  mostly in west; were recently formed (recENT) o Gelisols  Permafrost layers; in the polar and alpine regions; freezing   Soils of very cold climates that contain 2 meters of the surface  These soils are limited geographically to the high latitude polar regions  and localized areas at high mountain elevations   Has a high percentage of organic matter because of the slow rate of  microbial decomposition in cold climates  o Histosols  Organic soils; cover a small area (2% of US); essentially peatlands, large  carbon; living tissue; mostly organic matter  o Inceptisols  Few diagnostic features; adolescent in various environments, young soils;  beginning of soils in their life  o Mollisols  Soft, dark, 22% of the US; excellent for agriculture o Oxisols  highly weather and leached; warm, rainy areas; soils with large amounts of oxygen containing compounds o Spodosols  Acid, sandy forest soils; coniferous forests; wood ash; ashy soils  o Ultisols  Soils that have had the last of their nutrient bases leached out; clay  accumulation with low bases o Vertisols


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