Mineral Horizons/Layers

The soil horizon and layer definitions and methods for field description that follow are taken or modified from Agriculture Canada Expert Committee on Soil Survey (1997), Green et al. (1993), and Luttmerding et al. (1990).

24. Horizon/Layer

Record the mineral horizon or layer designation followed by lowercase modifiers, e.g., Btg.

Codes for major horizons:
A	Mineral horizon, containing < 17% organic C by mass, that has formed at or near the soil surface in the zone of leaching or eluviation of organic materials in solution or suspension, or of maximum in situ accumulation of organic matter, or both.
B	Mineral horizon characterized by enrichment in organic matter, sequioxides, or clay; or by the development of soil structure; or by a change of colour denoting hydrolysis, reduction, or oxidation.
C	Mineral horizon comparatively unaffected by the pedogenic processes operative in the A and B horizons, except the process of gleying (Cg), and the accumulation of calcium and magnesium carbonates (Cca) and more soluble salts (Cs, Csa).

Codes for layers:
R	Consolidated bedrock layer which is too hard to break with the hands.
W	Layer of water in Gleysolic, Organic, or Cryosolic soils.
Lowercase modifiers:
b	Buried soil horizon.
c	Irreversibly cemented horizon (ortstein, placic, duric, and CaCO3 cemented layers are examples).
ca	Horizon > 10 cm thick of secondary carbonate enrichment in which the concentration of lime exceeds that in the unenriched parent material.
cc	Irreversibly cemented concretions.
e	Horizon characterized by the eluviation of clay, Fe, Al, or organic matter alone or in combination.
f	Horizon enriched with amorphous material, principally Al and Fe combined with organic matter. It must have a hue of 7.5YR or redder, or its hue must be 10YR near the upper boundary and becomes yellower with depth. When moist the chroma is higher than three or the value is three or less. It is used primarily with the Bf, Bhf, Bfg, and Bgf codes. The following f horizons are differentiated on the basis of the organic C content:
	Bf 0.5-5% organic C Bhf > 5% organic C
g	Horizon characterized by gray colours, or prominent mottling, or both, which indicates of permanent or periodic intense reduction. Chromas of the matrix are generally one or less. It is used with the Aeg, Bg, Bfg, Bgf, Bhfg, Btg, Cg, Ckg codes, and others. When used with the Ae, Bf, Bhf, and Bt codes, the limits set for the other modifiers must be met. The Bgf horizons are usually prominently mottled; more than half of the soil material occurs as mottles of high chroma. The Bgf horizons occur in Fera Gleysols and Fera Humic Gleysols and possibly below the Bfg of gleyed Podzols.
h	Horizon enriched with organic matter. It is used with the Ah, Ahe, Bh, and Bhf codes.
	Ah - An A horizon enriched with humified organic matter; at least one colour value unit lower that the underlying horizon, or 0.5% more organic C than the C horizon or both.
	Ahe - An Ah horizon that has undergone eluviation as evidenced by streaks and splotches of different shades of gray, and often by plated structure.
	Bh - Contains > 1% organic C with less than 0.3% pyrophosphate-extractable Fe [Fe(p)] and a ratio of C : Fe(p) of 20 or more (very rare in British Columbia).
	Bhf - Defined under f above.
j	Used with e, f, g, n, and t to denote an expression of, but failure to meet, the specified limits of the letter code it modifies. It is placed to the right of the letter it modifies.
k	Denotes the presence of carbonate as indicated by visible effervescence when a dilute HCl solution is added.
m	Horizon slightly altered by hydrolysis, oxidation, or solution, or all three to give a change in colour or structure, or both. It is used with the Bm, Bmgj, Bmk, and Bms codes.
	It has:
	1. Evidence of one of or more of the following:
	higher chromas and redder hues than the underlying horizons; enrichment or complete removal of carbonates either as Bmk or Bm; and/or change in structure from that of the original material.
	2. Illuviation too slight to meet requirements of a Bt or podzolic B.
	3. No cementation or induration and lacks a brittle consistence when moist.
n	Horizon with distinctive prismatic or columnar structure, dark coatings on ped surfaces, and hard to very hard consistence when dry; the exchangeable Ca to exchangeable Na is 10 or less. It is used with Bn or Bnt codes.
p	Horizon disturbed by human activities, such as cultivation, logging, and habitation.
s	Horizon with salts, including gypsum, which may be detected as crystal or veins, or as surface crusts of salt crystals. It is used with any combination of horizon codes.
sa	Horizon > 10 cm thick with secondary enrichment of salts more soluble than Ca and Mg carbonates; the concentration of salts exceeds that in the unenriched parent material.
t	An illuvial horizon enriched with silicate clay. It is used with the Bt, Btg, and Bnt codes and may be modified by j.
	To use Bt:
	The horizon must be at least 5 cm thick. If any part of an the eluvial horizon has < 15% total clay in the fine fraction (< 2 mm), the Bt horizon must contain at least 3% more clay and if > 40% total clay, then it must contain at least 8% more clay. If the eluvial horizon has > 15% and < 40% clay in the fine fraction, then the ratio of the clay in the Bt to that of the eluvial horizon must be 1.2 or more (e.g., Ae 25 % clay; Bt at least 30% clay). In massive soils, there should be oriented clay in pores and as bridges between sand grains. If peds are present, clay films (skins) should be visible on ped surfaces and in pores.
u	Horizon that is markedly disrupted by physical (e.g., blowdown of trees, mass movement, etc.) or faunal processes (e.g., burrowing animals), but not from cryoturbation.
x	Horizon of fragipan character; loamy subsurface horizon of high bulk density and very low organic matter. When dry, it is hard and seems to be cemented; when moist is has moderate to weak brittleness. Air-dried clods slake (crumble) in water.
y	Horizon affected by cryoturbation. It is used with any combination of horizon codes.
z	A frozen layer, it may be used with any horizon or layer code.

Mineral diagnostic horizons:

Chernozemic A

At least 10 cm thick;
Colour value darker than 5.5 dry and 3.5 moist, chroma is lower than 3.5 moist;
Organic C content 1-17% and C:N ratio < 17;
Structure, when dry, is neither massive and hard, nor single grained; and
Mean annual soil temperature of 0o C or higher and a soil moisture regime subclass drier than humid.

Duric horizon

A strongly cemented horizon that does not satisfy the criteria of a podzolic B horizon. Usually has an abrupt upper boundary and a diffuse lower boundary. Air-dried clods do not hydrate in water, and moist clods at least 3 cm thick usually can not be broken in the hands.

Fragipan horizon

See definition of "x" above.

Ortstein horizon

A strongly cemented Bh, Bhf, of Bf horizon at least 3 cm thick which occurs in more than one-third of the exposed pedon. Generally reddish brown to very dark reddish brown.

Placic horizon

A thin layer (commonly 5 mm or less thick) or a series of thin layers that are irregular or involuted, hard, impervious, often vitreous, and dark reddish brown to black.

Podzolic B horizon (field criteria only)

At least 10 cm thick;
Moist crushed color: hue is 7.5YR or redder or 10YR near the upper boundary and becomes yellower with depth. The chroma is higher than 3 or the value is 3 or less;
Accumulation of amorphous material is indicated by brown to black coatings on some mineral grains or brown to black microaggregates. Silty feel when the material is rubbed wet, unless cemented; and
Texture coarser than clay.

Solonetzic B horizon

The term includes both Bn and Bnt horizons.

Lithic layer

Bedrock (R) below a depth of 10 cm. The upper surface of a lithic layer is a lithic contact.

25. Depth

Record the average depths (in centimetres) of the upper and lower boundaries of the soil horizon being described, e.g., Ah 0-5, Bm 5-20. The top of the uppermost mineral horizon is considered as zero depth.

26. Colour

Soil colour is determined by comparison with Munsell Colour Charts . The notation for a specific colour should be in the order of hue, value/chroma. Intermediate hues, values, and chromas may be expressed with the use of decimals.

ASP - Colour Aspect

The colour of a soil varies with its moisture content and physical state. Record the aspect of the Munsell colour notation using the codes in Table 2.29.

TABLE 2.29. Colour aspects and codes for mineral soils

Code	Aspect	Description
1	Matrix moist	Matrix is the main soil constituent or material that encloses other soil features, for example, peds. This colour aspect is reserved for structureless soils or weakly structured soils whose peds crumble upon handling.
2	Matrix dry
3	Exped moist	Colour of ped surfaces in soils with moderately durable peds which may be broken open and examined.
4	Exped dry
5	Inped moist	Dominant colour of ped interiors in soils with moderately durable peds that may be broken open and examined.
6	Inped dry
7	Crushed moist	Soil material is crushed and mixed. Surface of the sample is smoothed to reduce irregularities that affect colour.
8	Crush dry

27. Texture

Soil texture is defined by the size distribution of primary mineral particles (2 mm diameter or less). The textural classes and codes are determined from the soil texture triangle by estimating the percentage of clay (less than 0.002 mm diameter) and sand (0.05 to < 2.0 mm diameter)(Figure 2.4). See Appendix 2.4 for a key to soil texture (and letter-code descriptions).

FIGURE 2.4. Soil texture triangle.

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28. Percent Coarse Fragments

Estimate the percent coarse fragment (> 2 mm diameter) volume in each size class and record the total percent. Describe the coarse fragment shape using the type codes in Table 2.30.

TABLE 2.30. Size classes and type codes for coarse fragments

Size Classes	Shape type: R, S, A^a	Shape type: T
Size Classes	Diameter (cm)	Length (cm)
G - Gravel	< 7.5	< 15
C - Cobbles	7.5-25	15-38
S - Stones and boulders	>25	> 38

^a type codes: R = rounded; S = subrounded and subangular; A = angular; T = thin, flat.

29. Roots

Describe roots by noting their abundance and size (Table 2.31). Record the most abundant size first; secondary roots can be recorded by using a slash (/) in the columns (see example in Item 21).

TABLE 2.31. Root abundance and size classes and codes

Size class		Very fine	Fine	Medium	Coarse
Code		V	F	M	C
Size (mm)		< 1	1 to 2	3 to 5	> 5
Abundance code and class X
X	None	0	0	0	0
F	Few	< 10^a	< 10	1	1
P	Plentiful	10-100	10-100	2-10	2-5
A	Abundant	> 100	> 100	> 10	> 5
^a Values represent number of roots of size class observed in reference area of 100 cm2

30. Structure

Record the kind and class of structure (see Table 2.32 below and Figure 2.5). When more than one kind of primary structure is present, record the dominant under structure, and the subordinate in comments.

TABLE 2.32. Codes for kind and class of soil particle structure

Kind	Class		Size (mm)^a
ABK: Angular blocky; peds bounded by flattened, rectangular faces intersecting at relatively sharp angles	VF	very fine angular blocky	< 5
	F	fine angular blocky	5-10
	M	medium angular blocky	10-20
	C	coarse angular blocky	20-50
	VC	very coarse angular blocky	> 50
SBK: Subangular blocky; peds bounded by slightly rounded, subrectangular faces with verticesb of their intersections mostly subrounded	VF	very fine subangular blocky	< 5
	F	fine subangular blocky	5-10
	M	medium subangular blocky	10-20
	C	coarse subangular blocky	20-50
	VC	very coarse subangular blocky	> 50
GR: Granular; spheroidal peds bounded by curved or very irregular faces that do not adjoin those of adjacent peds	VF	very fine granular	< 1
	F	fine granular	1-2
	M	medium granular	2-5
	C	coarse granular	5-10
	VC	very coarse granular	> 10
PL: Platy; peds flat or platelike; horizontal planes more or less well developed	VF	very fine platy	< 1
	F	fine platy	1-2
	M	medium platy	2-5
	C	coarse platy	5-10
	VC	very coarse platy	> 10
PR: Prismatic; vertical faces of peds well defined and verticesb angular (edges sharp); prism tops essentially flat	VF	very fine prismatic	< 10
	F	fine prismatic	10-20
	M	medium prismatic	20-50
	C	coarse prismatic	50-100
	VC	very coarse prismatic	> 100
COL: Columnar; vertical edges near top of columns not sharp (vertices^b subrounded); column tops flat, rounded, or irregular	VF	very fine columnar	< 10
	F	fine columnar	10-20
	M	medium columnar	20-50
	C	coarse columnar	50-100
	VC	very coarse columnar	> 100
SGR: single grained	Loose, incoherent mass of individual primary particles, as in sands
MA: Massive	Amorphous; a coherent mass showing no evidence of any distinct arrangement of soil particles; separates into clusters of particles, not peds
CDY:	Cloddy; not a structure, used to indicate the condition of some ploughed surfaces.
^a The size limits refer to measurements in the smallest dimension of platy, prismatic, and columnar peds, and to the largest of the nearly equal dimensions of blocky and granular peds.
^b Definition of vertex (plural, vertices): the intersection of two planes of a geometrical figure.

GradeThe degree of distinctness of aggregation of soil particles. If grade of structure is described, record with class code separated by a slash (e.g., S/VC = strong/very coarse).

W	=	Weak
WM	=	Weak to moderate
M	=	Moderate
MS	=	Moderate to strong
S	=	Strong

31. pH

Record pH by noting the method of measurement (see Table 2.26 under Item 22) and the determined values to one decimal place.

32. Comments

Record any observations or measurements that are unique, unconforming, or could be of particular significance to the study, classification, or management interpretations. Examples include: colour and description of mottles (see colour section), description of clay films, and porosity.

Mottling:

Described by recording abundance, size, and contrast and colour (see Tables 2.33 and 2.34). Use Munsell Colour Charts, defaulting to aspect 7, crushed moist, unless otherwise noted. For example, FMD 7.5YR mottles = few, medium, distinct, strong brown (crushed moist) mottles.

TABLE 2.33. Abundance and size codes for mottles

Abundance			Size
Code F C M	Class Few Common Many	% of exposed surface < 2 2-20 > 20	Code F M C	Class Fine Medium Coarse	Diameter (mm) < 5 5-15 > 15

TABLE 2.34. Contrast codes for mottles

Code	Description
F	Faint: Evident only on close examination. Faint mottles commonly have the same hue as the colour to which they are compared and differ by no more than 1 unit of chroma or 2 units of value. Some faint mottles of similar but low chroma and value can differ by 2.5 units of hue.
D	Distinct: Readily seen, but contrast only moderately with the colour to which they are compared. Distinct mottles commonly have the same hue as the colour to which they are compared, but differ by 2-4 units of chroma or 3-4 units of value; or differ from the colour to which they are compared by 2.5 units of hue, but by no more than 1 unit of chroma or 2 units of value.
P	Prominent: Contrast strongly with the colour to which they are compared. Prominent mottles are commonly the most obvious colour feature in a soil. Prominent mottles that have medium chroma and value commonly differ from the colour to which they are compared by at least 5 units of hue, if chroma and value are the same; by at least 4 units of value or chroma, if the hue is the same; or by at least 1 unit of chroma or 2 units of value, if hue differs by 2.5 units.

Clay films (skins):

Accumulations of oriented clay translocated from another part of the soil. Clay films are described by recording the frequency of occurrence, and estimated thickness (see Tables 2.35 and 2.36). Most Bt horizons will exhibit clay films and should be noted. For example, FMTK clay films = Few, moderately thick clay films.

TABLE 2.35. Clay film frequency classes

Code	Class	Description
X	None	No clay films present.
F	Few	Clay films cover less than 2% of the total area of the specified surface(s). Patches of film are identifiable, but their frequency is so low that the significance of their presence may be nil or doubtful.
C	Common	Clay films cover 2-20% of the total area of the specified surface(s).
M	Many	Clay films cover 20-80% of the total area of the specified surface(s). They may occur as discrete patches or as a continuous network.
CS	Continuous	Clay films cover more than 80% of the total area of the specified surface(s). Patches of these surfaces may be free of clay films, but the films are essentially continuous.

FIGURE 2.5. Diagrammatic representation of soil structure.

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FIGURE 2.5. (continued).

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TABLE 2.36. Clay film thickness classes

Code	Class	mm	Description
TN	Thin	< 0.05	Hand lens is needed for identification; visible in cross-section with 10X lens, but not to the unaided eye. If present, fine sand grains protrude through the film or are only thinly coated and are readily apparent.
MTK	Moderately thick	0.05-0.5	Clay films are visible in cross-section to the unaided eye. Fine sand grains are enveloped by the film or their outlines are indistinct. Film surfaces are relatively smooth.
TK	Thick	0.5-1.0	Clay films and their broken edges are readily visible without magnification. Film surfaces are smooth.
VTK	Very thick	> 1.0	Clay films are a striking feature of the morphology

Effervescence:

The bubbling, hissing, or foaming that occurs when a 10% HCl solution is added to a sample of soil. Enter the appropriate code from Table 2.37.

TABLE 2.37. Codes to describe degree of effervescence

Code	Class	Degree of effervescence
X	None	No evidence of effervescence
VW	Very Weak	Few bubbles. (Note: ensure that the crackling sound is from reaction rather than absorption of liquid; compare with water).
W	Weak	Bubbles readily observed
M	Moderate	Bubbles form low foam
S	Strong	Bubbles form thick foam

Horizon porosity:

An estimate of total pore volume that reflects the combined effects of soil structure and density. Record porosity classes for mineral horizons as described in Table 2.38.

TABLE 2.38. Mineral horizon porosity classes

Code	Porosity class	Description
S	Slightly porous	Closely packed structureless soil material; highly compacted material.
M	Moderately porous	Horizons with weak to moderate structure and moderately close packing; closely packed soils with large, well-developed peds.
H	Highly porous	Horizons that are loosely packed, and/or very well structured with small peds.

33. Profile diagram

Sketch a cross-sectional profile diagram of the horizon boundaries, and add other significant features (relative coarse fragment distribution and size, piping, turbation, seepage, water table, lithic contact, etc.) (see example, Figure 2.6).

FIGURE 2.6. Example of profile diagram.

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34. Notes

Use this section to summarize or describe soil features not otherwise recorded on the form or that are significant to the study, classifications, or management interpretations.

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