Master Horizons. O horizon A horizon E horizon B horizon C horizon R horizon W horizon O A E

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Randolph Shaw
5 years ago
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1 Soil Horizons

2 Master Horizons O horizon A horizon E horizon B horizon C horizon R horizon W horizon O A E B C R W

3 Master Horizons O horizon predominantly organic matter (litter and humus) A horizon zone of organic matter accumulation E horizon zone of eluviation (loss of clay, Fe, Al) B horizon zone of accumulation (clay, Fe, Al, CaC0 3, salts ) forms below O, A, or E horizon

4 Master Horizons C horizon little or no pedogenic alteration, unconsolidated parent material, soft bedrock R horizon hard, continuous bedrock

5 O horizon

6 A horizon

7 E horizon

8 B horizon

9 B horizon

10 B horizon

11 B horizon

12 C horizon

13 R horizon

14 Transitional Horizons contains properties of horizon above and horizon below AB mostly A horizon, but some B horizon BA mostly B horizon, but some A horizon BE mostly B horizon, but some E horizon BC mostly B horizon, but some C horizon CB mostly C horizon, but some B horizon C/B intermingled bodies of C and B horizon material, majority is C horizon material

15 Transitional Horizons EB BC

16 Transitional Horizons BE BC

17 Horizon Suffixes Horizon Suffix a b c e g h i k Criteria highly decomposed organic matter (O) buried genetic horizon (any) concretions or nodules (any) moderately decomposed organic matter (O) strong gleying (any) illuvial organic matter accumulation (B) slightly decomposed organic material (O) pedogenic carbonate accumulation (B or C)

18 Horizon Suffixes Horizon Suffix o p r s ss t v w x Criteria residual sesquioxide accumulation (B) plow layer or other artificial disturbance (A) weathered or soft bedrock (C) illuvial sesquioxide accumulation (B) slickensides (B) illuvial accumulation of silicate clay (B) plinthite (B) weak color or structure (B) fragipan (B)

19 Subhorizon Examples Ap Ap Bt Bt Btx Alfisol Ultisol

20 Subhorizon Examples O A E Bh Bs Bw A Bt C Bk Spodosol Aridisol

21 Subhorizon Examples Ap A1 A2 Bo Bk Mollisol Oxisol

22 Subhorizon Examples Oe Oa C Histosol Entisol

23 Subhorizon Examples Plinthic Kandiudult

24 Numerical Suffixes used to denote subdivisions within a master horizon A1 A2 Bt1 Bt2 Bt3 C1 C2

25 Numerical Suffixes Ap A Bt1 C1 Bt2 BC C2 C3 Entisol

26 Discontinuities changes in parent material or mode of deposition colluvium over residual limestone soil over sandstone bedrock A, E, Bt1, 2Bt2, 2Bt3, 2BC, 2C, 3R by convention, 1 is understood, but not shown

27 Discontinuities Ap Bw Bt1 Bt2 2R 2Bt1 loess over limestone residuum colluvium over residuum

28 Boundaries distinctness distance through which one horizon grades into another abrupt (0-2.5cm), clear (2.5-5cm), gradual (5-15cm), diffuse (>15cm) topography lateral undulation and continuity of the boundary between horizons smooth (planar), wavy (width>depth), irregular (depth>width), broken (discontinuous)

29 Boundaries abrupt smooth abrupt wavy

30 Boundaries clear smooth clear irregular

31 Boundaries gradual smooth diffuse smooth

32 Boundaries irregular broken

33 SOIL COLOR

34 SOIL COLOR Both use Munsell Notation

35 Munsell notation (cont.) The number before the slash is the Value. Value indicates the lightness of a color. The scale of value ranges from 0 for pure black to 8 for pure white. 7.5 YR 4 / 3 The number after the slash is the Chroma. Chroma describes how the intensity of a color. The scale ranges from 1 to 8. For neutral colors, chroma is 0.

shines on the color chart and the soil sample you are

Compare the color of the inside surface with the soil

36 Color Mechanics 1. Break the ped. If it is dry, moisten it slightly with water from your water bottle. 2. Stand with the sun over your shoulder so that sunlight shines on the color chart and the soil sample you are examining. 3. Compare the color of the inside surface with the soil color chart. Note: Sometimes, a soil sample may have more than one color. Record the colors and indicate (1) the matrix (dominant color) and (2) other colors (mottles or redox).

37 Color Mechanics Viewing Conditions? very cloudy days foggy days early morning late afternoon wintertime conditions. smoky conditions indoor artificial light nighttime??????

38 Inferred Soil Characteristics

39 Aquic Conditions soils with aquic conditions are those that undergo continuous or periodic saturation or reduction

40 Saturation endosaturation soil is saturated with water in all layers from the upper boundary of saturation to a depth of 200 cm or more from the mineral surface groundwater saturation episaturation water table is perched on top of an impermeable layer

41 Formation of Redoximorphic Features Anaerobic conditions soil is saturated so most all pores are filled with water, absence of oxygen Prolonged anaerobiosis changes the chemical processes in the soil Reduction of Fe and Mn oxides results in distinct soil morphological characteristics most are readily observable changes in soil color

42 Soil Color and Oxidation / Reduction In subsoil horizons, Fe and Mn oxides give soils their characteristic brown, red, yellow colors When reduced, Fe and Mn are mobile and can be stripped from the soil particles Leaving the characteristic mineral grain color usually a grayish color Red Soil Soil Color Coating of Fe2O3 Mineral grain (gray) Remove Fe Gray Soil

43 Types of Redoximorphic Features Redox Concentrations Masses Pore Linings Nodules and Concretions Redox Depletions Depleted Matrix Reduced Matrix

44 Redox Concentrations Bodies of apparent accumulation of Fe-Mn oxides Masses Pore Linings ped faces root channels Nodules and Concretions

45 Soft Masses Soft bodies frequently in the soil matrix variable shape can usually be removed from the soil intact

46 Soft Masses in Sand The masses have diffuse reddish boundaries

49 Depleted Matrix Dominant color of the soil is gray Commonly used to identify hydric soils

50 Describing Redoximorphic Features Concentrations and Depletions Describe type, color, abundance and location (i.e. along macropores or within matrix) contrast can be obtained from color charts Reduced Matrix Describe reduced matrix color, oxidized color, and time for color change to occur

51 Mottles - Quantity few <2% common 2 to <20% many (>20%)

52 Mottles - Size fine -- <2 mm medium -- 2 to 5 mm coarse -- 5 to 20 mm very coarse 20 to 76 mm extremely coarse -- >76 mm

53 Redox Concentrations Hard Fe/Mn nodule in matrix (likely relict) Pore linings on root channel Pore linings on ped surface Soft Fe mass in matrix Hard Fe/Mn concretion in matrix Hard Fe/Mn nodule in matrix (likely contemporary) Adapted from Fig 1, Vepraskas 1995 Schematic illustration showing different kinds of redox concentrations and their relationship to soil macropores and matrices

54 Interpretation Problems Redoximorphic features do not occur in all soils Low amounts of soluble Organic Carbon High ph Cold temperatures Low amounts of Fe Aerated groundwater

55 Rate of Feature Formation A 2 mm thick Fe depletion around a root channel ranged from less than 1 to greater than 100 years depending upon how long reducing conditions occurred and how much Fe was in solution each day Recently constructed wetlands should have redox depletions evident within a couple of years if wetland hydrology is present during the growing season

56 Age of Features Redox features do not always indicate current hydrologic condition commonly found in drained (historic) wetlands can be relict of past climates relict features may have sharp edges and abrupt boundaries with the soil relict nodules and concretions are often rounded contemporary features should have diffuse boundaries and / or be associated with ped faces or root channels

59 REVIEW 1 We describe color using Munsell Notation to accurately convey what we see to someone else. 2 Good viewing conditions are critical to accurate reading of a color. 3 If the sun is low colors are redder. 4 Cloudy days make it difficult to read low chroma colors. 5 Color is a critical characteristic when working with redoximorphic features 6 The location of color within the soil fabric can separate relict features from current conditions; the age of color. 7 Observable soil colors, accurately described, leads to critical inferred characteristics.

60 Soil Texture proportion by weight of sand, silt, and clay estimated in the field or measured in the laboratory placed into a texture class NOTE: soil texture is only the fine-earth fraction (< 2mm) particle size distribution is fine-earth plus rock fragments (>2mm)

61 Particle Sizes Sand 2 mm to 0.05 mm very coarse sand 1 to 2 mm coarse sand 0.5 to 1 mm medium sand 0.25 to 0.5 mm fine sand 0.10 to 0.25 mm very fine sand 0.05 to 0.10 mm Silt 0.05 to mm Clay -- < mm (<2 m)

62 Relative Sizes of Particles beachball frisbee dime Silt (feels floury) ( mm) Clay (feels sticky) (< mm) Sand (feels gritty) ( mm)

63 Texture Classes Class Abbrev. Class Abbrev. very coarse sand VCOS fine sandy loam FSL coarse sand COS very fine sandy loam VFSL sand S loam L fine sand FS silt loam SIL very fine sand VFS silt SI loamy coarse sand LCOS sandy clay loam SCL loamy sand LS clay loam CL loamy fine sand LFS silty clay loam SICL loamy very fine sand LVFS sandy clay SC coarse sandy loam COSL silty clay SIC sandy loam SL clay C

64 Texture Triangle 12 texture classes

65 Texture Flowchart

66 Rock Fragments -- Sizes SPHERICAL OR CUBELIKE gravel (2 75 mm diameter) GRAVELLY cobbles ( mm diameter) COBBLY stones ( mm diameter) STONY boulders (> 600 mm diameter) BOULDERY FLAT channers (2 150 mm long) CHANNERY flagstones ( mm long) FLAGGY stones ( mm long) STONY boulders (> 600 mm long) BOULDERY

67 Rock Fragments -- Roundness

68 Texture Modifiers Fragment Content (% volume) Rock Fragment Usage <15 no adjective used 15 to < 35 gravelly, cobbly, flaggy 35 to < 60 very gravelly, very cobbly 60 to < 90 extremely gravelly 90 gravel (no texture class)

69 Particle Size Classes Other Systems

70 Soil Structure soil structure is the naturally occurring arrangement of soil particles into aggregates resulting from pedogenic processes Each individual unit of soil structure is called a PED (Latin, earth) structure best observable in a pit or road cut with auger observations, look at structure at end of auger

71 Soil Structure granular blocky angular subangular platy prismatic columnar wedge structureless single grain massive

72 Granular (GR) spheroidal shape with curved or very irregular faces most common in A horizons high in organic matter content (>2%) microorganisms excrete lignin ( glue ) from humus to bind particles together commonly influenced by soil management

(less angular) more common in soils higher in kaolinite up to a

73 Blocky (ABK or SBK) common in B horizons, particularly in humid regions ABK (angular) more common in soils higher in smectite SBK (less angular) more common in soils higher in kaolinite up to a point, the more shrinking and swelling, the more angular the structure (PJT theory)

74 Prismatic (PR) most common in clayey subsoils height of ped is greater than width of ped; angular tops

75 Columnar (COL) similar to prismatic except has rounded tops found in soils high in Na

76 Platy (PL) width is wider than height commonly found in compacted soil horizons natural compaction fragipans dense basal till artificial compaction plow plans

77 Structureless single grain (SG) massive (MA)

78 Soil Structure - Grade Grade Code Criteria structureless 0 no discrete units observable in place in or hand sample weak 1 units are barely observable in place or in hand sample moderate 2 units well-formed and evident in place or in a hand sample strong 3 units are distinct in place and separate cleanly when disturbed

79 Soil Structure structureless single grain granular 2SBK 2SBK

80 3PR 1SBK 2SBK prismatic subangular blocky

81 Soil Structure Size

82 Soil Structure Size

83 Soil Consistence resistance of a soil particle (ped) at various moisture contents to mechanical stresses Wet soils Stickiness Plasticity Moist soils Dry soils nonsticky nonplastic loose loose slightly sticky slightly plastic very friable soft sticky plastic friable slightly hard very sticky very plastic firm hard very firm extremely firm very hard extremely hard

84 Soil Consistence

Loose: You have trouble picking out a single ped

it.* Friable: The ped breaks with a small amount

* Soils with single grained structure always

Firm: The ped breaks when you apply a good

85 Loose: You have trouble picking out a single ped and the structure falls apart before you handle it.* Friable: The ped breaks with a small amount of pressure. * Soils with single grained structure always have loose consistence. Firm: The ped breaks when you apply a good amount of pressure and dents your fingers before it breaks. Extremely Firm: The ped can t be crushed with your fingers.

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