111.%20Soil

111.%20Soil - Soil Lecture 11 Soil Lecture 11 Soil Page 1...

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Unformatted text preview: Soil Lecture 11 Soil Lecture 11: Soil Page 1 of 27 Lecture 11: Soil Formation Weathered material in place Aggregate of Earth materials Low strength Disaggregate in water Lecture 11: Soil Page 2 of 27 Lecture 11: Soil Formation A growth media for plants Dirt Dirt Lecture 11: Soil Page 3 of 27 Lecture 11: Soil Formation Contents Soil Forming Factors Parent material Parent Climate Climate Macro-climate Macro Micro-climate Micro Topography Topography Macro-topography Macro Micro-topography Micro Organisms Organisms Flora Flora Fauna Fauna Time Time Lecture 11: Soil Page 4 of 27 Lecture 11: Soil Formation Parent Material Establishes overall Establishes conditions Weatherability Weatherability Permeability Permeability Climate Establishes Moisture conditions Moisture Temperature Temperature conditions Lecture 11: Soil Page 5 of 27 Lecture 11: Soil Formation Topography Establishes gravity Establishes environment Controls microControls Climate Micro-Topography Establishes local water conditions Establishes Controls local erosion Controls Influences local plant growth Influences Lecture 11: Soil Page 6 of 27 Lecture 11: Soil Formation Organisms Mix materials Mix Add chemicals and organics Add Time Controls time-sensitive processes Controls Weathering Weathering Severe/Regular climatic events Severe/Regular Rate of surface renewal Rate Lecture 11: Soil Page 7 of 27 Lecture 11: Soil Formation Soil Profile Soil profiles reflect the environment in which the soil formed Lecture 11: Soil Page 8 of 27 Lecture 11: Soil Formation Role of MicroTopography Soil Classification Soil Lecture 11: Soil Page 9 of 27 Lecture 11: Soil Formation Entisol Very young soil without developed horizons Inceptisol Inceptisol Young soil with thin poorly developed horizons Lecture 11: Soil Page 10 of 27 Lecture 11: Soil Formation Histisol Mature soil developed in a wetland Alfisol Mature soil developed in a climatic region characterized by hardwoods Lecture 11: Soil Page 11 of 27 Lecture 11: Soil Formation Spodosol Mature soil developed in a cold and wet environment characterized by pine trees Mollisol Mollisol Mature soil in a semi-arid grassland environment Lecture 11: Soil Page 12 of 27 Lecture 11: Soil Formation Aridisol Mature soil developed in an arid environment Ultisol Old soil developed in a warm sub-tropical environment Lecture 11: Soil Page 13 of 27 Lecture 11: Soil Formation Oxisol Very old tropical soil deeply weathered -- most minerals have been weathered to their oxide form Soil Phase Relationships Lecture 11: Soil Page 14 of 27 Lecture 11: Soil Formation Soil-Water Relationships Soil Classification System Order (10)/Suborder (47) Order Differentiated by presence or absence of Differentiated diagnostic horizons and the dominant soil forming process Great Group (185)/Subgroup (970) Great Differentiated based on whole assemblage of Differentiated soil horizons and moisture/temperature regimes Lecture 11: Soil Page 15 of 27 Lecture 11: Soil Formation Soil Classification System Family (4500+) Family Category within subgroup that have similar Category physical and chemical properties Series (10,500+) Series Defined by a more limited range of Defined characteristics than the family grouping Soil Survey Map (Soil Series) (Soil BoA Boonville fine sandy loam, 0 to 1 percent slopes Lecture 11: Soil Page 16 of 27 Lecture 11: Soil Formation Soil Series Information Setting Setting Typical profile Typical Soil properties Soil Composition Composition Contrasting soils Contrasting Land uses Land Management concerns Management Interpretive groups Interpretive BoA — Boonville fine sandy loam, 0 to 1 percent slopes Setting Setting Landform: Uplands Landform: Landscape position: Footslopes Landscape Slope: Nearly level; slightly concave or plane Slope: Shape of areas: Elongated or oval Shape Size of areas: 50 to 150 acres Size Native vegetation: Open savannah with mid Native and tall grasses Lecture 11: Soil Page 17 of 27 Lecture 11: Soil Formation Boonville fine sandy loam Typical Profile Surface layer: Surface 0 to 17 inches—dark grayish brown, slightly acid fine to inches— sandy loam 17 to 41 inches—light grayish brown, neutral clay that 17 inches— has red and brown mottle Subsoil: Subsoil: 41 to 56 inches—light gray, moderately alkaline clay 41 inches— loam 56 to 73 inches—pale yellow, moderately alkaline 56 inches— clay loam 73 to 80 inches—light brownish gray, slightly alkaline 73 inches— shale that has clay texture Boonville fine sandy loam Soil Properties Depth class: Very deep Depth Drainage class: Somewhat poorly drained Drainage Depth to the water table: 0.5 to 1.0 foot (perched) Depth Flooding: None Flooding: Runoff: Slow Runoff: Permeability: Very slow Permeability: Available water capacity: Moderate Available Root zone: Very deep; restricted by the clay subsoil Root Natural soil fertility: Medium Natural Shrink-swell potential: High in the subsoil ShrinkHazard of water erosion: Slight Hazard Lecture 11: Soil Page 18 of 27 Lecture 11: Soil Formation Boonville fine sandy loam Composition This map unit consists of about 85 percent This Boonville soil and similar soils. Contrasting soils make up about 15 percent of the unit. Contrasting Soils Tabor soils, which have a yellowier subsoil than Tabor that of the Boonville soil; in landscape positions similar to those of the Boonville soil Zack and Zulch soils, which have a thinner Zack surface layer than that of the Boonville soil; on convex slopes Boonville fine sandy loam Land Uses Land Major land use: Pasture Major Other land use: Urban development Other Lecture 11: Soil Page 19 of 27 Lecture 11: Soil Formation Boonville fine sandy loam Management Concerns Pasture Pasture Major limitations: The moderate available water Major capacity and medium natural fertility limit the potential forage production. Cropland Cropland Major limitations: The moderate available water Major capacity and medium natural fertility limit yields of most crops. Minor limitations: Seasonal wetness is a concern in Minor most years. Rangeland Rangeland Major limitations: The moderate available water Major capacity and medium natural fertility limit the potential forage production. Boonville fine sandy loam Urban development Urban Major limitations: Structures and roads are affected Major by the high shrink-swell potential in the subsoil. shrinkDisposal of septic tank effluent is a concern because Disposal of the restricted permeability and short periods of soil saturation Interpretive Groups Interpretive Land capability classification: 3w Land Ecological site: Claypan Prairie Ecological Pasture management group: 7 Pasture Source: soils.usda.gov/survey/online Lecture 11: Soil Page 20 of 27 Lecture 11: Soil Formation Physical Properties of a Soil Soil structure Soil Particle-size distribution Particle Homogeneity/isotropy Homogeneity/isotropy Bulk density Bulk Particle density Particle Porosity Porosity Permeability Permeability Hydraulic conductivity Hydraulic Moisture capacity Moisture Matric potential Matric Soil Structure Arrangement and organization of the particles Arrangement within a soil Total porosity within a soil volume, shapes of Total individual pores and overall pore-size distribution Single-grained = particles are loose and Single unattached to each other (uncemented) Massive = particles are tightly packed or Massive bonded Aggregated = in between single-grained and Aggregated massive Lecture 11: Soil Page 21 of 27 Lecture 11: Soil Formation Particle-size distribution Description of the distribution of the various grain sizes within a soil sample GEOLOGIST (sorting) GEOLOGIST Well sorted = all the same size Well Poorly sorted = various sizes Poorly ENGINEER (grading) ENGINEER Well graded = various sizes Well Poorly graded = all the same size Poorly Homogeneity — Isotropy Description of the relative uniformity of a soil Description sample HOMOGENEOUS Physical properties are constant throughout the soil Physical ISOTROPIC Physical properties are uniform in all directions Physical COMMON ASSUMPTION Lecture 11: Soil Page 22 of 27 Lecture 11: Soil Formation Bulk Density Bulk (Mass of solids)/(Total volume) (Mass Clayey soils = 1.1 gm/cm3 Clayey Sandy soils = 1.6 gm/cm3 Sandy Particle Density Particle (Mass of solids/Volume of solids) (Mass Quartz = 2.65 gm/cm3 Quartz Porosity (Science/geology) Porosity (Volume of voids)/(Total volume) (Volume Void Ratio (Engineering) Void (Volume of voids)/(Solids volume) (Volume Permeability Permeability Ability of a solid material to allow the flow of a fluid Ability through it under a hydraulic gradient of 1 Hydraulic Conductivity Hydraulic Ability of a solid material to allow the flow of WATER Ability through it under a hydraulic gradient of 1 Moisture Capacity Moisture Natural moisture content 2-3 days after a soaking rain Natural 2(Weight water)/(Weight solids) (Weight 18—30% as function of clays 18— Lecture 11: Soil Page 23 of 27 Lecture 11: Soil Formation Matric Potential Tenacity with which water is held within soil pores — capillary effect and adsorption dominate Controlled by: Controlled Pore size Pore Fluid properties Fluid Degree of saturation Degree Chemical Properties of a Soil Cation exchange capacity Cation pH, Acid/Base pH, eH, Redox potential eH, Humic content Humic Lecture 11: Soil Page 24 of 27 Lecture 11: Soil Formation Cation Exchange Capacity The total amount of exchangeable cations The that can be held by a soil Expressed in terms of milliequivalents per Expressed 100 grams of soil at pH = 7.0 (Neutral) Examples Clay = 2-150 meq/100g Clay Organic soil > 200 meq/100g Organic Sand = 2-7 meq/100g Sand pH — Acid/Base pH is negative log of the Hydrogen (H+) ion pH concentration in a aqueous solution Representative Examples Representative bleach……….…….13 bleach……….…….13 ammonia………….12 ammonia………….12 sea water…………..9 sea water…………..9 distilled water…...…8 distilled water… ...… pure rain……………6 pure rain……………6 beer/most fish……..5 beer/most fish……..5 vinegar……………..4 vinegar……………..4 lemon juice………...3 lemon juice………...3 Base Acid Lecture 11: Soil Page 25 of 27 Lecture 11: Soil Formation Redox Potential (eH) Measure of the affinity of a substance to take on Measure or give up electrons Measures “activity” of all dissolved species Measures Include both oxidizing and reducing species Include Measured in volts — transfer of electrons Measured generates an electrical current Often influenced by organics (microorganisms) Often +eH = oxidization +eH -eH = reducing conditions Humic Content Organic material that has undergone Organic enough degradation (weathering) to make the parent material unrecognizable (carbon content) Usually less than 10% Usually Slightly soluble in water Slightly Resistant to biodegradation Resistant Influenced by agricultural practices Influenced Lecture 11: Soil Page 26 of 27 Lecture 11: Soil Formation Break Lecture 11: Soil Page 27 of 27 Lecture 11: Soil Formation ...
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This note was uploaded on 04/16/2011 for the course GEOL 320 taught by Professor Mathewson during the Spring '11 term at Texas A&M.

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