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Soil Science Exam 1
| Question | Answer |
|---|---|
| Define soil | A relatively thin surface layer made up of a mixture of weathered mineral particles, decaying organic matter, living organisms, gases, and liquid solutions. |
| Pedosphere definition | Soil mantle of the Earth, is the intersection of the lithosphere, atmosphere, hydrosphere, and biosphere. It comprises soil at the land surface through interactions of soil-forming factors such as parent material, climate, organisms, topography, time. |
| what are the 5 factors of soil formation? | CL - climate O - organisms (Vegetation/Biology) R - Relief(Topography) P - Parent Material T - Time |
| what are the 4 internal processes of soil formation? | Additions: OM input or windblown sediments. Removals(losses): leaching or erosion, Translocations: Movement of inorganic or organic material, and Transformations: The weathering of primary particles (from the PM) |
| Soil in the Neolithic revolution | Fertile soils in areas like the Fertile Crescent and the Jordan Valley were crucial for supporting early agriculture. This began land degredation. |
| Land Degredation | Began as soon as agriculture began so not a recent problem. This led to the collapse of civilizations like the Mayans. Our current disconnect from soil and abuse of it for agriculture leads to further degradation. |
| what are the 12 soil orders? | Inceptisol Andisol Mollisol Alfisol Spodosol Ultisol Aridisol Vertisol Entisol Histosol Oxisol Gellisol |
| Epipedons | Mollic, Umbric, Ochric, Melanic, Histic. Plaggen and Anthropic as well. |
| Diagnostic Subsurface Horizons | Albic, Argillic, Spodic, Oxic, Cambic, Kandic, Sombric, Sulfuric, Natric, Agric, Calcic, Gypsic, Salic, Duripan, Fragipan, Placic. |
| Argillic Horizon (Bt) | Illuvial accumulation of silicate clays (not formed in place), Illuvial based on overlying horizon, Clay bridges, Clay coatings (argillans), Bt horizons. |
| What is the difference between organic and mineral soil? | Organic soil is primarily composed of decaying OM making it rich in nutrients, water-retentive, and well-structured. While Mineral soil is mainly weathered rock particles, such as sand, silt, and clay, and has a lower percentage of OM. |
| What is Humus? | Rich organic material of plant and animal origin in a stage of decomposition. |
| What is the difference between Elluviation and Illuviation? | eluviation is a loss of material from a layer, whereas illuviation is an enrichment or buildup of that material in a deeper layer |
| What is the importance of soil color? | It can tell you what minerals something has in it or if its been Elluviated like an E horizon what it lacks. |
| What is the importance of physical soil properties? | They regulate water infiltration and water retention, influence root penetration, and affect the exchange of gases essential for soil life and plant growth. |
| What are the primary components of soil? | 25% air, 25% water, 5% OM, 45% mineral matter (clay, sand or silt particles). |
| Podzolization | Occurs in the Spodic horizon. Mobilization and eluviation of AL and Fe from the O, A, and E horizons, and the immobilization of these metals in short-range order complexes with OM. Driven largely by production of organic acids from decomp of plant mats |
| Lessivage | Happens in Alfisols, Clay translocation (lessivage) in aqueous solution. Loss of clay from A and E horizons by dispersion and lateral transport. Dissolution of clays from A and E horizons. Leaching of dissolved constituents |
| Melanization | Happens in Mollisols, is the process of darkening of the soil by addition and decomposition of OM. |
| Laterization | Happens in Oxisols, the process by which silica is removed from the upper layers by alkaline leaching, while oxides of Fe and Al remain behind. |
| Gilgai Relief | A characteristic undulating surface of mounds and depressions that forms in soils with high clay content and significant shrink-swell potential, such as Vertisols. Highs and lows spaced about 3 to 10m |
| Spodic Horizon | Rapidly formed. sandy soils with little clay to inhibit podzolization under forest or heath vegetation. Illuvial accumulation of OM and Al, dark colored with a low base saturation(acidic). Formed under humid acid conditions. |
| Albic Horizon | (white) horion, because it is light colored and low in clay, Fe, and Al oxides due to elluviation. Generally sandy texture with low chemical reactivity (low CEC). Typically overlies Bh or Bt. Usually an E horizon but not all E are this. |
| Fragipan | Btx, Bx, Ex. A hard, cement-like soil layer that forms about 15 to 50 cm (6 to 20 inches) or more below the surface, restricting root growth and water movement. |
| Slickensides | A grooved surface in soil that forms from friction as two surfaces rub against each other. In soils, they are created by the expansion and contraction of clay minerals during wet and dry cycles, and are a key indicator of a soil type called a vertisol |
| What are common suborders? | Aquepts: Wet Inceptisols. Gelepts: Cold Inceptisols. Cryepts: Very cold Inceptisols. Ustepts: Inceptisols of semi-arid or subhumid climates. Xerepts: Inceptisols of Mediterranean climates. Udepts: Inceptisols of humid climates |
| Soil Temperature Regimes | Frigid Lower than 8° C Mesic 8° C to 15° C Thermic 15° C to 22° C Hyperthermic 22° C or higher |
| Bw horizon | Weakly developed B |
| Bt horizon | Horizon with clay films usually argillic. |
| O A E B C R | Master Soil Horizons |
| Organo-Argillans | A buildup in a B horizon made up of OM and clay combined. |
| Plinthite | humus-poor, iron-rich material with mottled red, yellow, and gray colors. (firm, iron oxide-rich concentration) as a continuous phase in a layer. A Fe rich mixture of clay with quartz and other minerals |
| Wassents (Subaqueous Entisol) | Inundated by fresh water, dominated by sandy textures, containing sulfidic materials, very low load-bearing capacity (high n value), with an irregular decrease/increase in carbon content with increasing depth, and with minimal evidence of soil development |
| Patterned ground | Common in Gelisols, it is formed from the freeze and thaw of ground and is a symmetrical natural pattern of geometric shapes. |
| Fibric | Would be peat (Oi) and have a raw reddish color, mostly undecomposed. Greater than 40% of volume is identifiable fibers after being rubbed. |
| Critical zone science (may not be on exam) | Earth's permeable near-surface layer from the tops of trees to the bottom of active cycling groundwater. Where rock, soil, water, air, and living organisms interact and shape Earths surface. Critical to Clean water, productive soil, balanced atmosphere. |
| How can Climate affect soil formation? | Temperature and moisture affect chemical reaction speed, weathering, Dissolution, Chemical Decomposition, organic decomposition, leaching, and deposition of soil components. |
| How can organisms affect soil formation? | Plant roots spread out, animals burrow, and bacteria eat. These speed up the breakdown of large soil particles into smaller ones. Roots can crack rocks and produce carbon dioxide that mixes with water and forms an acid that wears rock away. |
| How can Relief(Topography) affect soil formation? | The shape of the land and the direction in faces makes a difference in how much sunlight the soil gets, and how much water it keeps. Deeper soils form at the bottom of a hill than at the top because gravity and water move soil particles down the slope. |
| How can Parent Material affect soil formation? | soil inherits traits from the material from which it formed. Soils that form in limestone bedrock are rich in calcium, Soils that formed from materials at the bottom of lakes are high in clay. |
| How can Time affect soil formation? | Allows for Chemical weathering to occur and minerals to change into more broken down or stable forms like clay. Erosion also can occur and break down the PM more. |
| What is a Soil Profile? | A vertical cross-section of layers of soil found in a given area. Below are two examples of soil profiles. |
| What is the O-Horizon? | Surface-layer, at depths of 0-2 feet, dark in color, soft in texture. Has a lot of Humus. Also contains leaf litter - leaves, needles, twigs, moss, lichens that are not decomposing. Several O-layers can occur in some soils, consisting only of O-horizons |
| What is the A-Horizon? | “Topsoil”/ “Biomantle”. Top layer of mineral soil, at depths of 2-10 feet Some humus present, darker in color than layers below Biomantle - most biological productive layer; earthworms, fungi, and bacteria live this layer. Granular structure bc of life. |
| What is the E-Horizon? | Known as the Leeching layer, a small layer between A and B at depths of 10-15 feet deep. Light in color and mainly sand or silt. Poor mineral and clay content due to the leeching occuring. |
| What is the B-Horizon? | The "Subsoil" Horizon at depths of 10-30 feet. Rich in clay minerals like Fe and Al. Red/brown in color due to oxides of Fe & clay. Plant roots can extend into this layer. |
| What is the C-Horizon? | The "Regolith" Horizon made up of large rocks or lumps of partially broken bedrock. Least affected layer by weathering and have changed the least since their origin as PM. Devoid of OM bc of how far down in the soil profile it is. |
| What is the R-Horizon? | The "Bedrock" Horizon, deepest horizon in the profile. Continuous mass of bedrock, colors are of original rock of the area. |
| Pedogenisis | The process by which soil forms. |
| Hemic | Would be Mucky Peat (Oe), intermediate between muck and peat. Between 17% and 40% of volume is identifiable fibers after being rubbed. |
| Sapric | Muck (Oa), well decomposed and black in color. Less than 17% of volume is identifiable fibers after being rubbed. |
| Mollic Epipedon | Dark color, thick and soft. Usually found under grass in grasslands. |
| Umbric Epipedon | Similar to Mollic, has a low base saturation and is in an area of high rainfall. PM has lower Ca and Mg |
| Ochric Epipedon | Thin light colored, low in OM. Hard and massive structure when dry. |
| Melanic Epipedon | Black OM rich, developed from volcanic ash. |
| Histic Epipedon | OM overlying mineral soil, formed in wet areas. Black to dark brown peat or muck with low bulk density. |
| Plaggen Epipedon | Produced by long term manuring, 100s of years old and 50 cm thick. |
| Soil Moisture Regimes | Aquic (or Perudic): Saturated with water long enough to cause oxygen depletion. Udic: Humid or subhumid climate. Ustic: Semiarid climate. Aridic (or Torric): Arid climate. Xeric: Mediterranean climate (moist, cool winters and dry, warm summers) |
| Soil Temperature Regimes For soil families that have a difference of less than 5° C between the mean summer and mean winter soil temperatures. | Isofrigid Lower than 8° C Isomesic 8° C to 15° C Isothermic 15° C to 22° C Isohyperthermic 22° C or higher |
| What are the Moisture Regimes based off of. | Based on the watertable level and the presence or absence of available water (used by plants). All moisture regimes, except aquic, are based on regional climate. Aquic moisture regimes are based on the length of the period that the soil was saturated. |
| Permafrost | Soil that remains at or below 0 Celsius for at least 2 years. |
| Biological Crust | Intricately intertwined lichens, cyanobacteria, mosses, and algae. Stabilize soil surface against wind and erosion, does not impede water infiltration |
| Desert Crust | Thin surface layer of uncemeted fine earth, Coherent when dry. Can be broken free from underlying soil material, 10 to 20mm thick, Impedes infiltration and seeding |
| Desert Pavement | a flat, stony surface in arid regions where wind and water erosion have removed fine-grained sediment, leaving a closely packed layer of larger rocks |
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