Soil Texture 5/15/2012. Soil and Site. Lindbo et al. DRAFT 1

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1 Soil Texture 5/15/2012 Soil and Site. Lindbo et al. DRAFT 1

2 NDWRCDP Disclaimer This work was supported by the National Decentralized Water Resources Capacity Development Project (NDWRCDP) with funding provided by the U.S. Environmental Protection Agency through a Cooperative Agreement (EPA No. CR ) with Washington University in St. Louis. These materials have not been reviewed by the U.S. Environmental Protection Agency. These materials have been reviewed by representatives of the NDWRCDP. The contents of these materials do not necessarily reflect the views and policies of the NDWRCDP, Washington University, or the U.S. Environmental Protection Agency, nor does the mention of trade names or commercial products constitute their endorsement or recommendation for use.

3 CIDWT/University Disclaimer These materials are the collective effort of individuals from academic, regulatory, and private sectors of the onsite/decentralized wastewater industry. These materials have been peer-reviewed and represent the current state of knowledge/science in this field. They were developed through a series of writing and review meetings with the goal of formulating a consensus on the materials presented. These materials do not necessarily reflect the views and policies of North Carolina State University, and/or the Consortium of Institutes for Decentralized Wastewater Treatment (CIDWT). The mention of trade names or commercial products does not constitute an endorsement or recommendation for use from these individuals or entities, nor does it constitute criticism for similar ones not mentioned.

4 Citation - Stolt, M. H., Lindbo, D.L., R. Miles, D. L. Mokma, and S. Greene Field Description of Soils: Texture Power Point Presentation. in (D.L. Lindbo and N. E. Deal eds.) Model Decentralized Wastewater Practitioner Curriculum. National Decentralized Water Resources Capacity Development Project. North Carolina State University, Raleigh, NC.

5 Soil Texture Use texture to make inferences into pore size From pore size begin to estimate water movement and treatment Finer texture means slower water movement Finer texture means greater treatment Texture by itself is not enough information to determine site suitability

6 Other factors that combine with texture Soil structure Organic matter and vegetation Soil mineralogy Land use Landscape position Parent material Soil wetness

7 Soil Texture Mineral material only Material > 2mm are coarse fragments Material < 2mm only Sand mm Silt mm Clay - < mm

8 Soil Texture (mineral material only) Sand - gritty Silt - smooth, velvety Clay - slick, sticky

9 Systems for Classifying Particle Size Distributions USDA System (ie. Sandy Loam) AASHTO: American Association of State Highways (ie. A-1) Unified Engineering (ie. SM) Wentworth (phi #)

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11 USDA Particle-Size Distribution Fine-earth fraction: Finer than 2 mm: Used for Soil Textural Class Rock fragments: 2 mm in diameter or larger. Particles less than 10 are many times called coarse fragments. Used to modify textural class.

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14 USDA Textural Classes (12) Sand Loamy Sand Sandy Loam Loam Silt Loam Silt Sandy Clay Loam Silty Clay Loam Clay Loam Sandy Clay Silty Clay Clay

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16 Examples 5/15/2012 Soil and Site. Lindbo et al. DRAFT 16

17 40 % Sand 40 % Silt 20 % Clay Sand + Silt + Clay = 100% Texture = LOAM

18 25 % Sand?? % Silt 45 % Clay

19 25 % Sand 30 % Silt 45 % Clay

20 25 % Sand 30 % Silt 45 % Clay CLAY

21 65 % Sand 20 % Silt?? % Clay

22 65 % Sand 20 % Silt 15 % Clay

23 65 % Sand 20 % Silt 15 % Clay SANDY LOAM

24 ?? % Sand 30 % Silt 30 % Clay

25 40 % Sand 30 % Silt 30 % Clay

26 40 % Sand 30 % Silt 30 % Clay CLAY LOAM

27 Particle-Size Distribution Particle size distribution describes the abundance (by weight) of the various size particles that constitute the mineral portion of soil materials.

28 Fine-earth fraction Sand mm Silt 50 2 um Clay - < 2 um

29 Sand Fractions Fraction Size (mm) Very coarse sand to 1.0 Coarse sand to 0.5 Medium sand to 0.25 Fine sand to 0.10 Very fine sand to 0.05

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31 Textural Groups for OSWW Group I: Sand, Loamy sand Group II: Sandy loam, Loam, Group III: Sandy clay loam, Silt loam, Clay loam, Silty clay loam, Silt Group IV: Sandy clay, Silty clay, Clay

32 Textural Groups for OSWW Group I: Sand, Loamy sand gpd/ft 2 Group II: Sandy loam, Loam gpd/ft 2 Group III: Sandy clay loam, Silt loam, Clay loam, Silty clay loam, Silt gpd/ft 2 Group IV: Sandy clay, Silty clay, Clay gpd/ft 2

33 LOAM 40 % Sand 40 % Silt 20 % Clay LTAR = gpd/ft 2

34 25 % Sand 30 % Silt 45 % Clay CLAY LTAR = gpd/ft 2

35 65 % Sand 20 % Silt 15 % Clay SANDY LOAM LTAR = gpd/ft 2

36 40 % Sand 30 % Silt 30 % Clay CLAY LOAM LTAR = gpd/ft 2

37 Determining Texture 5/15/2012 Soil and Site. Lindbo et al. DRAFT 37

38 Determination of Texture Field procedure Laboratory procedure Hydrometer Pipette

39 Field Determination of Texture 5/15/2012 Soil and Site. Lindbo et al. DRAFT 39

40 Field 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. Soil Texture Class Key* Does soil form a ball or cast? No - the texture is SAND

41 Soil does not form a cast: Textural class is SAND

42 Field determination of texture Can the ball be handled No - the texture is LOAMY SAND. OR When pressing the soil between thumb and forefinger does the soil form a ribbon that extends beyond your forefinger? No - the texture is LOAMY SAND.

43 Forms a cast of moist soil material. Textural class is LOAMY SAND

44 The length of the ribbon will depend on mineralogy as well as clay content Making a ribbon

45 Field determination of texture If the soil forms a ribbon that that extends past the forefinger, note the length of the ribbon. Next excessively wet a small sample in the palm and rub with the forefinger.

46 Field determination of texture If the ribbon was < 1 inch long when it broke and the excessively wet sample feels: gritty, the texture is SANDY LOAM; smooth, the texture is SILT LOAM; neither gritty nor smooth, the texture is LOAM.

47 Field determination of texture If the ribbon was between 1 and 2 inches long when it broke and the excessively wet sample feels: gritty, the texture is SANDY CLAY LOAM; smooth, the texture is SILTY CLAY LOAM; neither gritty nor smooth, the texture is CLAY LOAM.

48 Field determination of texture If the ribbon > 2 inches long when it broke and the excessively wet sample feels: gritty, the texture is SANDY CLAY; smooth, the texture is SILTY CLAY; neither gritty nor smooth, the texture is CLAY.

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50 Laboratory Determination of Texture 5/15/2012 Soil and Site. Lindbo et al. DRAFT 50

51 Laboratory Determination of Particle-Size Distribution Percent sand and rock fragments are determined by a weight percent remaining in a sieve. Silt and clay fractions are determined based on how fast a particle of a given size falls in a sedimentation column.

52 Determining Percent Silt and Clay (Hydrometer) Based on Stokes Law Uses a 100 gram sample Particles dispersed w/ calgon Measures concentration of solids in suspension by suspension density Less time consuming Less accurate

53 Determining Percent Silt and Clay (Pipette) Based on Stokes Law Uses a 10 gram sample Particles dispersed w/ calgon Measures concentration of solids in suspension by weight More time consuming More accurate

54 Stoke s Law The settling time of a particle of a given density falling in a liquid of a given viscosity is proportional to the square of the particles radius. What does this mean? Bigger particles fall faster!!! and If we know the viscosity of the liquid and the density of the particles we can figure out their size.

55 Stokes Law: V = 2r 2 g(p s -p l )/(9n) V = velocity of fall r = particle radius g = acceleration due to gravity p s = particle density p l = liquid density n = fluid viscosity

56 At 20 o C how long does it take a 2um particle to fall 1 cm in a 0.5 g/l solution?

57 At 20 o C how long does it take a 2um particle to fall 1 cm in a 0.5 g/l solution? 8.41h/10h =.841h or 50.5 min.

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59 1000 ml Sedimentation Column

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62 Plunger for mixing soil in column

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70 Pipette Setup: Lowy Pipette Pump Stand Bell Jar Sieve Funnel

71 25 ml Lowy Pipette for silt and clay determination

72 Is there texture beyond just Sand, Silt and Clay? And so what if there is. 5/15/2012 Soil and Site. Lindbo et al. DRAFT 72

73 Textures Classes with Sand-Size Modifiers Coarse sand (CoS): >25% very coarse and coarse sand Fine sand (FS): >50% fine sand Very Fine sand (VFS): >50% very fine sand Loamy coarse sand (LCoS): >25% very coarse and coarse sand Loamy fine sand (LFS): >50% fine sand Loamy very fine sand (LVFS): >50% very fine sand

74 Textures Classes with Sand-Size Modifiers Coarse sandy loam (CoSL): >25% very coarse and coarse sand Fine sandy loam (FSL): >30% fine sand Very Fine sandy loam (VFSL): >30% very fine sand

75 Terms for describing rock fragments. Rounded, subrounded, and irregular: Size (mm) Type Adjective 2 to 76...Gravels...gr...gravelly 2 to 5...Gravels...grf...fine gravelly 5 to 20...Gravels...grm...med. gravelly 20 to 76...Gravels...grc...coarse gravelly 76 to Cobbles...cb...cobbly 250 to Stones...st...stony >600...Boulders...by...bouldery

76 Terms for describing flat rock fragments. Size (mm) Type Adjective 2 to Channers...cn...channery 150 to Flagstones...fl...flaggy 380 to Stones...st...stony >600...Boulders...by...bouldery

77 Using Rock Fragment Modifiers 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 ie. "extremely gravelly loam."

78 Textural Groups for OSWW Group I: Sand, Loamy sand Group II: Sandy loam, Loam, Group III: Sandy clay loam, Silt loam, Clay loam, Silty clay loam, Silt Group IV: Sandy clay, Silty clay, Clay

79 Relating Texture to Hydraulics 5/15/2012 Soil and Site. Lindbo et al. DRAFT 79

80 Pore Space

81 Median percolation rates for 220 subsoil horizons grouped by textural class. Textural Class cm/hr in/hr Number of Observations Silty Clay Loam a* 22 Silt Loam a 33 Clay Loam a 18 Silty Clay ab 9 Loam ab 71 Clay ab 16 Fine Sandy Loam b 19 Sandy Loam b 17 Loamy Coarse Sand b 5 Loamy Sand b 4 Sandy Clay Loam b 6 Coarse Sand b 2 Data taken from Matelski *Medians with different letters are significantly different at the 0.05 level.

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83 Interpreting Textural Rules of thumb: Modifiers As coarse fragments (CF) increase loading rates decrease As CF becomes platy loading rates decrease As sands become finer loading rates decrease

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89 Organic Matter 5/15/2012 Soil and Site. Lindbo et al. DRAFT 89

90 Organic Matter in Soils Coloring agent Water holding capacity Fertility Cementing agent for aggregation Organic matter may feel smooth (like silt) and sticky (like clay) and therefore interfere with your texture by feel

91 Organic Matter Subdivisions Organic Soil Materials Mineral Organics Mineral

92 Organic Matter Subdivisions Muck Mucky Mineral Mineral

93 Organic Carbon Content % Organic Carbon Muck Mucky Mineral Mineral % Clay

94 Identifying Organic Material by Feel Difficult to do without practice Need to practice on samples with known carbon contents

95 Types of Soil Organic Materials Sapric (Oa) Very decomposed, <17% rubbed fibers Hemic (Oe) decomposed, 17 to 40% rubbed fibers Fibric (Oi) least decomposed, > 40% rubbed fibers

96 Types of Soil Organic Materials Sapric (Oa) Muck Hemic (Oe) Mucky Peat Fibric (Oi) Peat Mineral Organic Mucky Sandy Loam

97 Type of Organic Soil Muck Highly decomposed. < 1/6 fibers remaining after rubbing. Sapric material Mucky Peat Moderately decomposed. Between 1/6 and ¾ fibers remaining after rubbing. Hemic material Peat Slightly decomposed. > ¾ fibers remaining after rubbing. Fibric material.

98 Identifying Organic Soil Type Rub moist sample between fingers 10 times Examine material with hand lens Look for fibers not live roots... and estimate percent Fibers are smaller than 2 cm (approx. 1 ) and show cellular structure

99 Knowing about texture can keep you from getting stuck if nothing else