Soil Judging Manual

Soil Judging Manual

Fall Semester, 2003

Table of Contents / Page Number
A. Morphology / 2
Horizonation / 2
Horizon Boundary / 5
Texture / 9
Color / 12
Structure / 13
Moist Consistence / 15
Redoximorphic Features / 15
B. Soil Profile Characteristics / 16
Hydraulic Conductivity / 16
Effective Rooting Depth / 17
Water Retention to 1 m / 18
Soil Drainage Class / 19
C. Site Characteristics / 20
Landform / 20
Parent Material / 20
Slope / 21
Slope Profile / 21
Surface Runoff / 23
D. Soil Classification / 24
Epipedon / 24
Diagnostic Subsurface Horizons and Features / 28
Orders, Suborders, and Great Groups / 33
Family Particle-Size Control Section and Class / 40
E. Site Interpretations / 43
Appendix - Abbreviations / 47
List of Great Groups / 48

A. Morphology

Horizonation

soil horizon - A layer of soil or soil material approximately parallel to the land surface and differing from adjacent genetically related layers in physical, chemical, and biological properties or characteristics such as color, structure,texture, consistency, kinds and number of organisms present, degree of acidity or alkalinity, etc.

Prefix:

None (dashed) - standard, soil is of same parent material throughout

2, 3, 4, ... - lithologic discontinuity in parent materials, dramatic change in color, texture, or rock fragments indicating contrasting parent materials

Master:

O - organic surface layers

A - mineral surface layers. The surface horizon of a mineral soil having maximum organic matter accumulation, maximum biological activity, and/or eluviation of materials such as iron and aluminum oxides and silicate clays

E - eluviated, stripped or bleached horizon, having less clay content and a lighter color than horizons above and below.

B - illuviated, accumulation or enrichments or clay, organic matter, or iron and aluminum oxides and/or blocky or prismatic structure.

C - unconsolidated material underlying the A and B horizons, relatively unaffected by soil forming processes

R - hard bedrock (not diggable)

Subordinate:

(O) i - slightly decomposed organic matter (fibric)

e - moderately decomposed organic matter (hemic)

a - highly decomposed organic matter (sapric)

(A) dashed - wavy, uneven boundary, found in uncultivated areas

p- plowed, having a smooth, flat boundary

(E) dashed - common

g - gleyed, matrix color with chroma of 2 or less, frequently found directly above a limiting horizon that perches water

(B) * All B horizons must have a subordinate horizon (i.e. no dashes)

Primary:

t - illuvial accumulation of clay. Illuvial means that the clay moved into the horizon.

h - humus accumulation (black colors)

s - iron accumulation (red colors) – usually for Spodosols

hs - iron and humus accumulation, value and chroma of 3 or less – usually for Spodosols

Secondary:

x - fragipan - see below

g - gleyed, matrix color with chroma of 2 or less (can be used alone or following t, x, or tx)

Tertiary:

w - "weak B" - other B horizons that don't have any of above characteristics

g - gleyed, matrix color with chroma of 2 or less

r - "rotten rock" - slightly weathered or soft bedrock (saprolite)

(R) dashed

Note: b - buried horizon - can be used with any of the above master-subordinate horizons

' - Bisequal soils - A prime (') is used for the second of two horizons with the same master-subordinate name that are separated by a different horizon (rare)

Fragipans

Fragipans are dense, brittle horizons that restrict water and root penetration. The following properties are generally found in fragipans in Pennsylvania (from Ciolkosz et al., 1995):

¨ Low organic matter content

¨ Loamy texture (without high clay or sand content)

¨ Firm or very firm, brittle consistence (moist state)

¨ High bulk density

¨ Low permeability

¨ Distinctive dark brown color that contrasts with the color of the cambic or argillic horizon above it (this feature often not observed in red parent materials)

They usually have:

¨ Prism faces gray in color with a bright yellowish brown zone just inside the gray zone.

Horizon Number

Use numbers to distinguish between consecutive horizons with identical master-subordinate names. Note, the prefix may differ. For example:

Ap / Oi
E / A
Bt1 / Bt
Bt2 / Btg1
2Bt3 / Btg2

Boundary

Depth - the lower depth of the horizon described

Distinctness:

a - abrupt, < 2 cm

c - clear, 2 - 5 cm

g - gradual, 5 - 15 cm

d - diffuse, > 15 cm (generally not used except in tropics - use a transitional horizon instead)

FOR ORGANIC HORIZONS, ONLY THE BOUNDARY AND COLOR ARE MEASURED, EVERYTHING ELSE IS DASHED.

Rock Fragment Modifier

SIZE AND SHAPE

Flattened / Not flattened
ch - channery (0.2 - 15 cm) / g - gravelly ( 0.2 - 7.5 cm)
fl - flaggy (15 - 38 cm) / cb - cobbly (7.5 - 25 cm)
st - stony (38 - 60 cm) / st - stony (25 - 60 cm)
bd - bouldery (> 60 cm) / bd - bouldery (> 60 cm)

ABUNDANCE

< 15% - no modifier (dashed)

15 - 35% - use size and shape modifier only (e.g., g or gravelly)

35 - 60% - very, (abbreviation is "v") (e.g., vg or very gravelly)

60 - 90% - extremely, (abbreviation is "e") (e.g., eg or extremely gravelly)

Soil texture - The relative proportions of the various soil separates in a soil as described by the classes of soil texture. The textural classes may be modified by the addition of suitable adjectives when rock fragments are present in substantial amounts; for example, "stony silt loam." The sand, loamy sand, and sandy loam are further subdivided on the basis of the proportions of the various sand separates present.

Class

sic - silty clay / l - loam
scl - sandy clay loam / cl - clay loam
sc - sandy clay (very rare) / si - silt
c - clay / sil - silt loam
ls - loamy sand - requires sand modifier / sicl - silty clay loam
s - sand - requires sand modifier / sl - sandy loam - requires sand modifier

Modifiers for loamy sand, sandy loam, and sand classes:

c - coarse - dominated by very coarse and coarse sand

none - medium - dominated by medium sand

f - fine sand - dominated by fine sand

vf - very fine sand - dominated by very fine sand

examples: vfs, fsl, lcs, lvfs, sl

sand classes:

very coarse sand 2 - 1 mm diameter

coarse sand 1 - 0.5 mm

medium sand 0.5 - 0.25 mm

fine sand 0.25 - 0.1 mm

very fine sand 0.10 - 0.05 mm

Clay Percentage - determined by texturing

TEXTURING

Texturing is perhaps the most important skill used in soil investigations. The soil texture helps determine horizon designation and depths. Soil hydraulic conductivity and root penetration are most affected by the texture of the underlying soil. While soil texture can be determined in a laboratory, a soil scientist, who may investigate tens of sites in a day, textures soil in the field.

There is no one way to texture soil. Many soil scientists texture many different ways. Enclosed is several different methods for determining texture. Each method has its own merits; some techniques may work for you and some may not. During the course of this class, you will probably develop texturing techniques that are unique to you only; that is all right, as long as it works. A professional soil scientist becomes proficient at texturing because of repetition; comparing the relative differences between the unknown sample and known samples that the soil scientist previously textured. It takes time and experience to become proficient at texturing.

Here are a couple of clues:

1. Always texture with your non-writing hand - if you don't, you'll smudge your description sheet.

2. Grittiness and/or crunching - presence of sand in the texture

3. Flour-like particles and ruffles in texture - presence of silt

4. Texture takes a long time to moisten and is extremely sticky when moist - presence of clay

Color - found by using Soil Color Charts Book

Hue - A measure of the chromatic composition of light that reaches the eye. Page of color book, Y = yellow, R = red, pages range from red to olive green

Value - The degree of lightness or darkness of a color in relation to a neutral gray scale. On a neutral gray scale, value extends from pure black to pure white. Numbers read vertically on each page; the higher the number, the lighter the color.

Chroma - The relative purity, strength, or saturation of a color. For those that like a technical definition: directly related to the dominance of the determining wavelength of the light and inversely related to grayness. Or, in simpler terms, chroma measures the amount of pigment (as opposed to white and black) in a color. A flourescent color has a very high chroma, a black and white TV show has zero chroma. Numbers read horizontally on each page; the higher the number, the brighter the color.

Example: 5 YR 4/6 - hue is 5 YR, value is 4, chroma is 6.

Reading soil color:

- Colors for A horizons are read from a crushed, but not smeared, sample.

- Colors for other horizons are read from the moist interior of a broken ped face.

- Whenever possible, read colors in direct sunlight, preferably with the sun to your back.

- Many colors are actually between chips or pages in the color book. This doesn't mean that you are not coloring well, this is reality. Use the closest color possible.

Structure

soil structure - The combination or arrangement of primary soil particles into secondary units or peds. The secondary units are characterized on the basis of size, shape, and grade (degree of distinctness)

Grade

A grouping or classification of soil structure on the basis of inter- and intra-aggregate adhesion, cohesion, or stability

Structureless (0) - no discrete units observable in place or in hand sample (usually in C horizons).

Weak (1) - units are barely observable in place or in a hand sample.

Moderate (2) - units well-formed and evident in place or in a hand sample. Usually need to be in the pit to see.

Strong (3) - units are distinct in place (undisturbed soil), and separate cleanly when disturbed. Usually can see from outside of the pit.

Shape

For grade structureless:

massive (m) - no structural units, material is a coherent mass (not necessarily cemented. Soil falls out in chunks as they are dug out with a knife (usually found in C horizons)

single grained (sg) - no structural units, entirely noncoherent; e.g., loose sand.

For other grades (also see diagram on following page):

granular (gr) - small polyhedrals, with curved or very irregular faces (common in A horizons, rare in subsurface horizons).

angular blocky (abk) - blocks with faces that intersect at sharp angles, usually found in textures with high clay content (most often in B horizons)

subangular blocky (sbk) - blocks with sub-rounded and planar faces, lack sharp angles.

prismatic (pr) - vertically elongated units with flat tops

platy (pl) - thin, horizontally bedded plates (found in E horizons, fragipans, and compacted A horizons)

Moist Consistence

loose (l) - intact specimen not obtainable

very friable (vfr) - specimen fails under very slight force between fingers.

friable (fr) - specimen fails under slight force between fingers.

firm (fi) - specimen fails under moderate force between fingers.

very firm (vfi) - specimen fails under strong force between fingers.

extremely firm (efi) - specimen fails under moderate force between hands.

Consistence generally gets firmer with increasing clay content and changing structure from weak to strong.

Redoximorphic Features (old term was mottles)

redoximorphic features - Soil properties associated with wetness that result from the reduction and oxidation of iron and manganese compounds in the soil after saturation with water and desaturation, respectively

redox depletions - Zones of low chroma (2 or less) where Fe-Mn oxides alone or both Fe-Mn oxides and clay have been stripped out of the soil.

redox concentrations - Zones of apparent accumulation of Fe-Mn oxides in soils (bright colors)

Abundance (see diagram on following pages for visuals of 2 and 20%)

None (dashed) - no redoximorphic features

Few (f) - < 2% of soil matrix

Common (c) - 2 - 20% of soil matrix

Many (m) - > 20% of soil matrix

Contrast (see table and chart on following pages for more exact measures)

Faint (f) - generally can only be seen upon close examination

Distinct (d) - generally can be seen while standing in the pit

Prominent (p) - generally can be seen from outside of the pit

B. Soil Profile Characteristics

Hydraulic Conductivity - an expression of the readiness with which water flows through a soil in response to a given potential gradient

In the field, saturated HC (Ksat) is estimated from texture, organic matter content, structure, and consistence:

High (> 3.6 cm/hr)

organic materials

s, ls textures

sl, l textures that are loose because of high organic matter content

fragmental soils: large volume of coarse fragments with insufficient fines

Medium (.036 - 3.6 cm/hr)

materials excluded from high and low classes

Low (< .036 cm/hr)

c, sc, sic textures with moderate (2) or weaker structure

sicl textures with weak structure

fragipans (Bx, Bxg, Btx, Btxg horizons)

dense glacial till (Cd horizons)

hard bedrock (R)

horizontally bedded soft bedrock with few vertical fractures (Cr horizons)

Surface

The surface hydraulic conductivity is based on the first described horizon.

Limiting Layer

The limiting layer is the least conductive layer in the soil profile. Note: the surface may be the limiting layer. In this area, there often is a fragipan or heavy clay layer in the subsoil which is more limiting.

Effective Soil Depth (Rooting Depth)