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Soil Texture

Soil Texture. Presented by: Mr. Brian Oram, PG, PASEO Wilkes University GeoEnvironmental Sciences and Environmental Engineering Department Wilkes - Barre, PA 18766 570-408-4619 http://www.water-research.net. S o i l T e x t e. Your Hands will Get “Dirty”. Quick Review.

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Soil Texture

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  1. Soil Texture Presented by: Mr. Brian Oram, PG, PASEOWilkes UniversityGeoEnvironmental Sciences and Environmental Engineering DepartmentWilkes - Barre, PA 18766570-408-4619 http://www.water-research.net

  2. Soil Texte Your Hands will Get “Dirty”

  3. Quick Review

  4. Major Components of Soil • Soil Space (50%) • Organic Matter • Mineral Matter Pore Space (50%) • This may contain air and/or water

  5. Master Soil Horizons • O Horizon- leaf litter / humus • A Horizon- organic accumulation in mineral soil • E Horizon- leached horizon (elluviation) • B Horizon- zone of illuviation • C Horizon – unconsolidated parent material • R Horizon – Lithic material (Rock) R Not All the Master Horizons Will Be Present in All Profiles

  6. Mineral Soil • Is never saturated with water for more than a few days and contains less than 20 % (by weight) organic carbon • Is saturated with water for longer periods or artifically drained and excluding live roots, has an organic-carbon content of: • Less than 18 % if the mineral fraction contains 60% or more clay; • Less than 12 %, if the mineral fraction contains no clays; or • Less than 12 + (clay percentage multiplied by 0.1) %, if the mineral fraction contains less than 60%. Soil material containing more than the above organic carbon is an organic soil.

  7. Describing Soil Morphologyfor Mineral Soil • Soil Texture and Coarse Fragment Content • Soil Structure • Soil Color • Consistency • Redoximorphic Features • Boundaries

  8. Soil Texture • Describes the mineral content of the soil - Which is typically less than 50% of the soil volume. • Soil texture is based on a weight ratio of the 3 soil separates (sand, silt, and clay). • Material > 2mm are coarse fragments or “rock fragments” and used as a modifier to the soil texture term. Modifier used only when the fragments represent more than 15 % of the soil volume. • Material < 2mm represent the three (3) soil separates. • Sand - 2.0 - 0.05 mm - GRITTY Feel ! • Silt - 0.05 - 0.002 mm – Talc – Floury Feel ! • Clay - < 0.002 mm – Tends to be Sticky when Wet !

  9. Particle Size Classification Systems • USDA System – Soil description for agricultural, land-based wastewater disposal, and most environmental applications. (i.e., loam) • AASHTO: American Association of State Highways and Transportation Projects – potential use as road base (i.e., A-1) • Unified Soil Classification System (ASTM D2487-92) Engineering Applications (i.e., SM) • Wentworth (phi #)- Geological and Geotechnical Studies Using screen or sieve size using the phi number. (phi #, sieve no., or mm) Each system has unique (“jargon” or terminology)

  10. The Systems Do Not Group the Soil Separates the Same

  11. USDA Particle-Size Distribution • This is the Particle System we will use in the course. • System is divided into: fine-earth fraction and rock fragments. • Fine-earth fraction: Finer than 2 mm: This is the information used to describe the soil and is the Soil Textural Class, such as sandy loam. Classification based on weight of 3 soil separates. • Rock fragments: 2 mm in diameter or larger. These are commonly described as part of the coarse fragment content. • The rock fragment modifier is based on a volumetric fraction of the soil and is used as a soil modifier. Therefore – Gravels made up 30 % of the volume for a sandy loam the full description would be gravelly sandy loam.

  12. Fine-earth fractionThe Three Soil Separates • Sand - 2.0 - 0.05 mm • Silt – 50 – 2 um • Clay - < 2 um

  13. Sand (S) Loamy Sand (LS) Sandy Loam (SL) Loam (L) Silt Loam (SIL) Silt (SI) Sandy Clay Loam (SCL) Silty Clay Loam (SICL) Clay Loam (CL) Sandy Clay(SCL) Silty Clay(SIC) Clay ( C) USDA and NRCS Textural Classes (12)

  14. Sand + Silt + Clay = 100% 40 % Sand 40 % Silt Texture = LOAM 20 % Clay

  15. The 21 Subclasses in Soil Texture • There are 12 soil texture classes. • When a sand modifier is added there can be 21 total subclasses, but 22 subclasses if very coarse sandy loam is included. FractionSize (mm) Very coarse sand.....................................2.0 to 1.0 Coarse sand.............................................1.0 to 0.5 Medium sand.........................................0.5 to 0.25 Fine sand..............................................0.25 to 0.10 Very fine sand......................................0.10 to 0.05

  16. SANDS (5) Very Coarse Sand(VCOS) Coarse Sand (COS) Sand (S) Fine Sand (FS) Very Fine Sand (VFS) LOAMY SANDS (4) Loamy Coarse Sand (LCOS) Loamy Sand (LS) Loamy Fine Sand (LFS) Loamy Very Fine Sand (LVFS) Soil Texture Subclasses

  17. SANDY LOAMS (4) Coarse Sandy Loam (COSL) Sandy Loam (SL) Fine Sandy Loam (FSL) Very Fine Sandy Loam|(VFSL) LOAMS (3) Loam (L) Silt Loam (SIL) Silt (SI) Soil Texture Subclasses

  18. CLAY LOAMS (3) Sandy Clay Loam(SCL) Clay Loam (CL) Silty Clay Loam (SICL) CLAYS (3) Sandy Clay (SC) Silty Clay (SIC) Clay ( C ) Soil Texture Subclasses

  19. Using Rock Fragment Modifiers • Divided into Spherical (cubelike) and Flat Units • Less than 15 percent: No adjective or modifier terms are used. • 15 to 35 percent: The dominant kind of rock fragment is used as an adjective ie. "gravelly loam”. • 35 to 60 percent: An adjective term with the word "very" is used ie. "very gravelly loam“. • More than 60 percent: An adjective term with the word “extremely" is used i.e., "extremely gravelly loam." NOTE: • > 90 %, less than 10 % soil separates it may be advisable to use the rock fragment modifier – such as gravel.

  20. Estimating Rock Fabric Content

  21. How Do We Determine Texture ?

  22. Determination of Texture • Field Procedure • The “Feel” Method • Estimating Sand and Clay Content • Field Test Kit – “Volume Method” • Laboratory Procedure • Hydrometer • Sieve • Pipette

  23. What Texture is This Material ?

  24. Field Determination of Texture- The Feel Method

  25. Method 1: The Feel Method • Key Features or Characteristic that We Use • Cast Formation and Stability • Feel – Grittiness, Floury, and Sticky • Ribbon Length • Evaluate Samples that are Moist, but note characteristics when the material is dry and wet. • See “Feel of Textural Classes” in Appendix C of the Course Documentation.

  26. Go to this Handoutin Appendix C of the Course Manual.

  27. Feel Method of Determination of Texture • Soil must be moist, not saturated; moist enough to mold like putty when you try to form a ball in your hand. • Question 1: Does soil form a ball or cast? • No - the texture is SAND • Question 2: Does the soil form a stable cast, but does not form a ribbon • No – the texture is loamy sand

  28. Thank You – Dr. David Lindo (NCSU) Soil does not form a cast: Textural class is SAND

  29. Feel Method of Determination of Texture (continued) • Question 3: Does soil form a weak ribbon less than 2.5 cm? • Yes - the possible textures are sandy loam, silt loam, or loam • Does the soil feel gritty? ------- Sandy Loam • Does the soil feels very smooth with some grittiness? ------ Silt loam • Does not feel gritty or smooth? ----- Loam

  30. The length of the ribbon will depend on clay content and mineralogy. Making a ribbon Thank You – Dr. David Lindo (NCSU)

  31. Feel Method of Determination of Texture (continued) • Question 4: Does soil form a ribbon from 2.5 to 5 cm? • Yes - the possible textures are sandy clay loam, silty clay loam, or clay loam • Does the soil feel gritty? ------- Sandy Clay Loam • Does the soil feels very smooth with some grittiness? ------ Silty Clay Loam • Does not feel gritty or smooth? ----- Clay Loam

  32. Feel Method of Determination of Texture (continued) • Question 4: Does soil form a ribbon > 5 cm? • Yes - the possible textures are sandy clay, silty clay, or clay • Does the soil feel gritty? ------- Sandy Clay • Does the soil feels very smooth with some grittiness? ------ Silty Clay • Does not feel gritty or smooth? ----- Clay

  33. Thank You – Dr. David Lindo (NCSU) Forms a cast of moist soil material. Textural class is LOAMY SAND

  34. Method 2: Estimating Sand and Clay Content • Collect a soil sample and remove the observable the coarse fragments, organic material (roots, etc), and other materials • If sample is dry, moisten the sample. Do not over wet or completely saturate the sample. • Knead sample between your thumb and finger and remove any other coarse fragments or non-soil aggregates. • Crush all the soil aggregates.

  35. Method 2: Estimating Sand and Clay Content • Question 1: Does the soil have more than 50 % sand? • Yes- Therefore, the sand texture is dominant and the likely soil textures are sandy clay loam, sandy clay, sandy loam, loamy sand, and sand. material (roots, etc), and other materials. • No – Therefore, the sand does not dominate and the likely soil textures are loam, silt loam, silt, clay loam, silty clay loam, silty clay, and clay.

  36. < 50 % > 50 %

  37. Method 2: Estimating Sand and Clay Content • Question 2: What is the range in clay content and is the sand content > 20 %? • The key is ribbon length and sand percentage. • Ribbon < 1 inch long – texture does not include the word clay. (sand, loamy sand, sandy loam, loam, silt loam, and silt) • Ribbon 1 to 2.5 inch (clay is 27 to 40 %), the soil texture includes the word clay. (sandy clay loam, clay loam, and silty clay loam) • Ribbon > 2.5 inch (clay > 40%), clay is the dominant name in the soil texture. (sandy clay, silty clay, and clay)

  38. Ribbon > 2.5inches Ribbon 1 to 2.5 inches Ribbon < 1 inch

  39. Method 2: Estimating Sand and Clay Content • Combine Your Observations • Sand content < 50 % • Ribbons 1.5 inch • Material has more of a floury feel and no real gritty feel. Sand content is likely under 20 % • When near saturated the material is sl. sticky. Therefore, the field evaluation would suggest that the soil has a clay modifier. It is likely that the soil is a silty clay loam.

  40. Method 3 – Volume Method Used to Estimate Soil Texture Based on a Non-Volume and Not on a Weight Bases This does not account for differences in material density, but settling rates on particle size.

  41. Method 4 – Hydrometer Method The Bouyoucos hydrometer method of mechanical analysis used in routine work, where quick measurements are necessary and extreme accuracy is not required. The method is based on the fact that water containing material in suspension has greater density than pure water. The more material in suspension, the greater the density. The Bouyoucos hydrometer measures the density of the suspension. The higher the hydrometer floats, the greater the density of the suspension. • Requirements: • Hydrometer- reading in grams • Electronic Balance • Dry Soil – 40 to 60 grams • Dispersing Agent • Use of an Oxidizing Agent (H202) • 1000 ml volumetric cylinder • Readings at 40 seconds and 3 hours • Temperature Correction

  42. Method 5 -Sieve AnalysisParticle-Size Distribution • Particle size distribution describes the abundance (by weight) of the various size particles that constitute the mineral portion of soil materials. • The distribution of the size based on mm, pH #, or sieze size is used for more detailed geological, engineering, and geotechnical applications. • Distribution of Particles for (Sand) can be used to estimate the permeability using the Hazen equations. • Laboratory Method

  43. Method 6 – Pipette Method • The pipet method utilizes Stoke's Law by the extraction of subsamples of the soil suspension at a given depth after a predetermined settling time for each size fraction of interest. • As time passes, larger particles pass by the sampling depth, and smaller and smaller size fractions can be sampled. • After extracting the sample, it is dried weighed, and a calculation can be done to determine the percentage of the total soil in suspension present in each sample. • The pipet method is very accurate, but also time consuming. Pretreatment of the sample may include the use of dispersing chemicals or oxidizing agents. V = (2gr²)(d1-d2)/9µ (Stokes Law) Where, V = velocity of fall (cm sec-¹), g = acceleration of gravity (cm sec-²), r = "equivalent" radius of particle (cm), dl = density of particle (g cm -³), d2 = density of medium (g cm-³), and µ = viscosity of medium (dyne sec cm-²).

  44. Time for Review ?

  45. Review • The three soil separates are ? • Mineral Particles Greater than 2 mm are? • Are all soil and textural classifications the same? sand, silt, and clay Coarse Fragments or Rock Fragments NO the classification systems are not the same !

  46. Soil Texture Presented by: Mr. Brian Oram, PG, PASEOWilkes UniversityGeoEnvironmental Sciences and Environmental Engineering DepartmentWilkes - Barre, PA 18766570-408-4619 http://www.water-research.net

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